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  • Structure Evolution of Self-catalyzed Grown Au, Ag and Their Alloy Nanostructure
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-21
    Zhu Zhu, Feng Chen, Chunxiang Xu, Guangcan Yang, Ye Zhu, Zhaoxu Luo

    Monitoring the nucleation and growth of nanomaterials is a key technique for material synthesis design and control. An efficient fabrication method can be realized deeply understanding the growth mechanisms. Here, noble metal nanostructures, gold (Au) nanoparticles, silver nanostructures (Ag nanoparticles/Ag nanowires) and gold-silver alloy nanoparticles were prepared in a facile method at room temperature. The growth processes of the Au nanoparticles, Ag nanowires and Au-Ag alloy nanoparticles can be monitored real-timely through the ultraviolet visible absorption (UV-vis), dynamic light scattering (DLS) and transmission electron microscopy (TEM). It is found that the whole formation involved Digestive ripening and Ostwald ripening cooperative mechanism. Furthermore, the self-assembly growth is noticed in the oriented attachment of precursor Ag monomers into nanowires under the same synthetic conditions without external templates or rigorous conditions. This result can provide a platform to discover the underlying growth mechanism of wet-chemistry methods for metal nanostructure fabrication.

    更新日期:2017-09-21
  • Ga originated kink-and-tail Zn diffusion profiles in InGaAsP and InGaAlAs alloys during MOVPE regrowth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-21
    T. Kitatani, K. Okamoto, K. Uchida, S. Tanaka

    We investigated the diffusion characteristics of Zn in ternary and quaternary alloys of InGaAsP and InGaAlAs, which are important materials in long-wavelength optical communication devices. The measured Zn diffusion profiles of InGaAs, InGaAsP, and InGaAlAs showed kink-and-tail shapes in which Zn concentration fell abruptly at first and then decreased slowly, whereas those of InP and InAlAs showed only abrupt decreases. Thus, only Ga-containing alloys had tail-like profiles. Since this tail was well described by the group-V vacancy related defect model, we deduced that its mechanism is closely related with group-V vacancies in Ga-related bonds such as GaP or GaAs. Furthermore, we demonstrated the possibility that many more group-V vacancies originated from GaP bonds than from GaAs bonds, indicating the difficulty in crystal growth of high quality alloys that have GaP components.

    更新日期:2017-09-21
  • High-quality AlN grown on a thermally decomposed sapphire surface
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-21
    S. Hagedorn, A. Knauer, F. Brunner, A. Mogilatenko, U. Zeimer, M. Weyers

    In this study we show how to realize a self-assembled nano-patterned sapphire surface on 2 inch diameter epi-ready wafer and the subsequent AlN overgrowth both in the same metal-organic vapor phase epitaxial process. For this purpose in-situ annealing in H2 environment was applied prior to AlN growth to thermally decompose the c-plane oriented sapphire surface. By proper AlN overgrowth management misoriented grains that start to grow on non c-plane oriented facets of the roughened sapphire surface could be overcome. We achieved crack-free, atomically flat AlN layers of 3.5 µm thickness. The layers show excellent material quality homogeneously over the whole wafer as proved by the full width at half maximum of X-ray measured ω-rocking curves of 120 arcsec to 160 arcsec for the 002 reflection and 440 arcsec to 550 arcsec for the 302 reflection. The threading dislocation density is 2∗109 cm-2 which shows that the annealing and overgrowth process investigated in this work leads to cost-efficient AlN templates for UV LED devices.

    更新日期:2017-09-21
  • Preparation of poly-Si Films by inverted AIC process on Graphite Substrate
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-20
    Lishuai Wei, Nuofu Chen, Kai He, Congjie Wang, YiMing Bai, Jikun Chen

    Graphite/a-Si/Al laminated structures were deposited on graphite substrate using magnetron sputtering technology. The temperature of depositing amorphous silicon (a-Si) and the Al/Si thickness ratio have strong influences on a-Si crystallization, Various conditions were used in order to investigate the polycrystalline silicon (poly-Si) thin films grown by inverted aluminum-induced crystallization (AIC) for process optimization. In this paper, we established the AIC model to explain the effects of the two factors in the inverted AIC process. The poly-Si thin films were characterized By means of Metallurgical microscope, X-ray diffraction (XRD), Raman spectroscopy (Raman), which showed that the samples with strong preferred (111) orientation and high crystallization quality that were favorable for epitaxially growing poly-Si thick film cells.

    更新日期:2017-09-21
  • The nucleation and growth mechanism of Ni-Sn eutectic in a single crystal superalloy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-20
    Weiguo jiang, Li Wang, Xiangwei Li, Langhong Lou

    The microstructure of single crystal superalloy with and without tin layer on the surface of as-cast and heat-treatment state was investigated by Optical microscope (OM) and scanning electron microscopy (SEM). The composition of different region on the surface was tested by energy dispersive X-ray (EDS). The reaction intermetallic compound (IMC) formed in the heat treatment process was confirmed by X-ray diffraction (XRD). The orientations of different microstructure in samples of as heat treatment state were determined by electron back-scattering diffraction (EBSD) method. The porosity location in the interdendrite region was observed by X-ray computed tomography (XCT).The experiment results showed that the remained Sn on the surface of the supealloy reacted with Ni, and then formed Ni3Sn4 in the as-cast state. Sn enriched by diffusion along the porosity located in the interdendrite region and γ+γ' (contain few of Sn) eutectic and Ni3Sn2 formed in single crystal supealloy during heat treatment, and the recalescence behaviors were found. Ni3Sn2 nucleated independently in the cooled liquid at the front of (γ+γ')(Sn) eutectic. The nucleation and growth mechanism of the eutectic and Ni3Sn2 IMC during heat treatment was discussed in the present paper.

    更新日期:2017-09-20
  • {111} facet growth laws and grain competition during silicon crystallization
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-19
    V. Stamelou, M.G. Tsoutsouva, T. Riberi-Béridot, G. Reinhart, G. Regula, J. Baruchel, N. Mangelinck-Noël

    Directional solidification from mono-crystalline Si seeds having different orientations along the growth direction is studied. Due to the frequent twinning phenomenon, new grains soon nucleate during growth. The grain competition is then characterized in situ by imaging the dynamic evolution of the grain boundaries and of the corresponding grain boundary grooves that are formed at the solid-liquid interface. To perform this study, an experimental investigation based on Bridgman solidification technique coupled with in situ X-ray imaging is conducted in an original device: GaTSBI (Growth at high Temperature observed by X-ray Synchrotron Beam Imaging). Imaging characterisation techniques using X-ray synchrotron radiation at ESRF (European Synchrotron Radiation Facility, Grenoble, France) are applied during the solidification to study the growth dynamics. Facetted / facetted grain boundary grooves only are studied due to their importance in the grain competition because of their implication in the twinning mechanism. The maximum undercooling inside the groove is calculated from the groove depth knowing the local temperature gradient. Additionally, thanks to dynamic X-ray images, the global solid-liquid interface growth rate and the normal growth rate of the {111} facets existing at the grooves and at the edges are measured. From these measurements, experimental growth laws that correlate the normal velocity of the {111} facets with the maximum undercooling of the groove are extracted and compared to existing theoretical models. Finally, the experimental laws found for the contribution to the undercooling of the {111} facets are in good agreement with the theoretical model implying nucleation and growth eased by the presence of dislocations. Moreover, it is shown that, for the same growth parameters, the undercooling at the level of the facets (always lower than 1 K) is higher at the edges so that there is a higher probability of twin nucleation at the edges which is in agreement with the grain structure development characterised in the present experiments as well as in the literature.

    更新日期:2017-09-20
  • Donor Impurity Incorporation during Layer Growth of Zn II-VI Semiconductors
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-18
    D.A. Barlow

    The maximum halogen donor concentration in Zn II-VI semiconductors during layer growth is studied using a standard model from statistical mechanics. Here the driving force for incorporation is an increase in entropy upon mixing of the donor impurity into the available anion lattice sites in the host binary. A formation energy opposes this increase and thus equilibrium is attained at some maximum concentration. Considering the halogen donor impurities within the Zn II-VI binary semiconductors ZnO, ZnS, ZnSe and ZnTe, a heat of reaction obtained from reported diatomic bond strengths is shown to be directly proportional to the log of maximum donor concentration. The formation energy can then be estimated and an expression for maximum donor concentration derived. Values for the maximum donor concentration with each of the halogen impurities, within these Zn II-VI compounds, are computed. The model predicts that the halogens will serve as electron donors in these compounds in order of increasing effectiveness as: F, Br, I, Cl. Finally, this result is taken to be equivalent to an alternative model where donor concentration depends upon impurity diffusion and the conduction band energy shift due to a depletion region at the growing crystal's surface. From this, we are able to estimate the diffusion activation energy for each of the impurities mentioned above. Comparisons are made with reported values and relevant conclusions presented.

    更新日期:2017-09-19
  • Influence of MBE growth modes and conditions on spontaneous formation of metallic In nanoparticles and electrical properties of InN matrix
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-15
    T.A. Komissarova, P. Wang, P. Paturi, X. Wang, S.V. Ivanov

    Influence of the molecular beam epitaxy (MBE) growth conditions on the electrical properties of the InN epilayers in terms of minimization of the effect of spontaneously formed In nanoparticles was studied. A three-step growth sequence was used, including direct MBE growth of an InN nucleation layer, migration enhanced epitaxy (MEE) of an InN buffer layer, and In-rich MBE growth of the main InN layer, utilizing the droplet elimination by radical-beam irradiation (DERI) technique. The three-step growth regime was found to lead to decreasing the relative amount of In nanoparticles to 4.8% and 3.8% in In-rich and near-stoichiometric conditions, respectively, whereas the transport properties are better for the In-rich growth. Further reduction of the metallic indium inclusions in the InN films, while keeping simultaneously satisfactory transport parameters, is hardly possible due to fundamental processes of InN thermal decomposition and formation of the nitrogen vacancy conglomerates in the InN matrix. The In inclusions are shown to dominate the electrical conductivity of the InN films even at their minimum amount.

    更新日期:2017-09-15
  • Crystal growth patterns in DC and pulsed plated galvanic copper films on [111], [100] and [110] oriented copper surfaces
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-12
    Delilah A. Brown, Sean Morgan, Vera Peldzinski, Ralf Brüning

    Copper films for printed circuit board applications have to be fine-grained to achieve even filling of vias. Electroplated Cu films on roll annealed Cu substrates may have unacceptably large epitaxial crystals. Here galvanic films were plated on oriented single-crystal Cu substrates from an additive-free electrolyte, as well as DC plating and pulse reverse (PR) plating with additives. The distribution of crystallite orientations was mapped with XRD and compared with the microstructure determined by SEM. For the additive-free bath on [111] and [100] oriented surfaces a gradual transition from epitaxial to polycrystalline is seen, while films on [110] substrates are persistently epitaxial. Without bath additives, twinning is the main mechanism for the transition to polycrystalline texture. For DC plating, additives (carriers, accelerators and levelers) promote fine-grained films with isotropic grain orientations, with films on [110] substrates being partially isotropic. Plating with carriers and accelerators (no leveler) yields films with many distinct crystallite orientations. These orientations result from up to five steps of recursive twinning. PR plating produces isotropic films with no or very few twins (<111> and <100> substrates, respectively), while on <110> oriented surfaces the deposits are about 20% epitaxial.

    更新日期:2017-09-13
  • Controlling the morphology transition between step-flow growth and step-bunching growth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-11
    Konrad Bellmann, Udo W. Pohl, Christian Kuhn, Tim Wernicke, Michael Kneissl

    Homoepitaxy on vicinal surfaces may proceed by either step-flow or step-bunching growth. This surface morphology transition is correlated with the inverse Ehrlich-Schwoebel barrier and the terrace width on the vicinal surface. We discuss a growth model based on the surface diffusion theory of Burton, Cabrera, Frank, and Schwoebel to account for conditions inducing the morphology transition. Based on a Monte-Carlo method, the transition conditions of the diffusion model are investigated regarding the inverse Ehrlich-Schwoebel barrier, the diffusion length, the vicinal terrace width, and the adatom mean resident time. This provides insights into crucial parameters and allows to predict the growth morphology by correlating theory and growth parameters. The theoretical results are applied to control the homoepitaxial growth of AlN.

    更新日期:2017-09-13
  • Sn – induced decomposition of SiGeSn alloys grown on Si by molecular-beam epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-08
    A.B. Talochkin, V.A. Timofeev, A.K. Gutakovskii, V.I. Mashanov

    Structural features of Si1-x-yGexSny alloy layers grown on Si by molecular-beam epitaxy are studied. These layers with the thickness of 2.0 nm, the nominal Ge composition of x0 ≈ 0.3, and the Sn-content of y≈ 2-6 at.% have been grown at low temperatures (100-150 °C). We have used high-resolution transmission electron microscopy to analyze atomic structure of grown layers and Raman spectroscopy to evaluate the real Ge-content x from the observed optical phonon frequencies. It is found that the x value coincides with the nominal one at low Sn-content (2-3 at.%), and when it is increased (y ≥ 5 at.%), the decomposition of alloys into two fractions occurs. One of them is enriched by Ge with x up to 0.6 and the other fraction is Si-enriched. It is shown that the observed decomposition is Sn-induced and related to increase in Ge adatoms mobility in the growth process. This mechanism is similar to that theoretically predicted by Venezuela and Tersoff (Phys. Rev. 58, 10871 (1998)) for the case of high growth temperature.

    更新日期:2017-09-13
  • Growth and characterization of an Al-doped GaSe crystal
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-07
    C.B. Huang, M.S. Mao, H.X. Wu, Z.Y. Wang, Y.B. Ni

    A GaSe: Al (0.13 wt.%) single crystal was grown using the Bridgman method combined with a crucible rotation technique. A 35×19×5.5 mm3 sample was cut from the as-grown crystal ingot. The GaSe: Al (0.13 wt.%) crystal has an indentation hardness of 2.27 GPa, which is 2.6 times harder than the pure GaSe crystal. In particular, a sample with a thickness of 5.5 mm has an infrared transmission of approximately 60%. The absorption coefficient of this sample is as low as 0.1 cm-1 over the range of 0.83 to -14 μm, which demonstrates its high optical quality. A crystal growth method with the described procedures may be suitable to grow other doped GaSe crystals.

    更新日期:2017-09-13
  • TaC-coated graphite prepared via a wet ceramic process: Application to CVD susceptors for epitaxial growth of wide-bandgap semiconductors
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-06
    Daisuke Nakamura, Taishi Kimura, Tetsuo Narita, Akitoshi Suzumura, Tsunenobu Kimoto, Kenji Nakashima

    A novel sintered tantalum carbide coating (SinTaC) prepared via a wet ceramic process is proposed as an approach to reducing the production cost and improving the crystal quality of bulk-grown crystals and epitaxially grown films of wide-bandgap semiconductors. Here, we verify the applicability of the SinTaC components as susceptors for chemical vapor deposition (CVD)-SiC and metal–organic chemical vapor deposition (MOCVD)-GaN epitaxial growth in terms of impurity incorporation from the SinTaC layers and also clarify the surface-roughness controllability of SinTaC layers and its advantage in CVD applications. The residual impurity elements in the SinTaC layers were confirmed to not severely incorporate into the CVD-SiC and MOCVD-GaN epilayers grown using the SinTaC susceptors. The quality of the epilayers was also confirmed to be equivalent to that of epilayers grown using conventional susceptors. Furthermore, the surface roughness of the SinTaC components was controllable over a wide range of average roughness (0.4 ≤ Ra ≤ 5 μm) and maximum height roughness (3 ≤ Rz ≤ 36 μm) through simple additional surface treatment procedures, and the surface-roughened SinTaC susceptor fabricated using these procedures was predicted to effectively reduce thermal stress on epi-wafers. These results confirm that SinTaC susceptors are applicable to epitaxial growth processes and are advantageous over conventional susceptor materials for reducing the epi-cost and improving the quality of epi-wafers.

    更新日期:2017-09-13
  • Sublimation growth of bulk 3C-SiC using 3C-SiC-on-Si (100) seeding layers
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-06
    P. Schuh, M. Schöler, M. Wilhelm, M. Syväjärvi, G. Litrico, F. La Via, M. Mauceri, P.J. Wellmann

    We have developed a transfer process of 3C-SiC-on-Si (100) seeding layers grown by chemical vapor deposition onto a poly- or single-crystalline SiC carrier. Applying subsequent sublimation growth of SiC in [100] direction resulting in large area crystals (up to ≈≈11 cm2) with a thickness of up to approximately 850 μμm. Raman spectroscopy, Laue X-ray diffraction and electron-backscattering-diffraction revealed a high material quality in terms of single-crystallinity without secondary polytype inclusions, antiphase boundaries or double positioning grain boundaries. Defects in the bulk grown 3C-SiC, like protrusions with surrounding stressed areas, stem from the epitaxial seeding layer. The presented concept using 3C-SiC-on-Si seeding layers reveals a path for the growth of bulk 3C-SiC crystals.

    更新日期:2017-09-13
  • MOVPE growth of violet GaN LEDs on β-Ga2O3 Substrates
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-05
    Ding Li, Veit Hoffmann, Eberhard Richter, Thomas Tessaro, Zbigniew Galazka, Markus Weyers, Günther Tränkle

    We report that a H2-free atmosphere is essential for the initial stage of metalorganic vapour phase epitaxy (MOVPE) growth of GaN on β-Ga2O3 to prevent the surface from damage. A simple growth method is proposed that can easily transfer established GaN growth recipes from sapphire to β-Ga2O3 with both (-201) and (100) orientations. This method features a thin AlN nucleation layer grown below 900 °C in N2 atmosphere to protect the surface of β-Ga2O3 from deterioration during further growth under the H2 atmosphere. Based on this, we demonstrate working violet vertical light emitting diodes (VLEDs) on n-conductive β-Ga2O3 substrates.

    更新日期:2017-09-13
  • Single Crystal growth of 67%BiFeO3-33%BaTiO3 solution by the floating zone method
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-01
    Y. Rong, H. Zheng, M.J. Krogstad, J.F. Mitchell, D. Phelan

    The growth conditions and the resultant grain morphologies and phase purities from floating-zone growth of 67%BiFeO3-33%BaTiO3 (BF-33BT) single crystals are reported. We find two formidable challenges for the growth. First, a low-melting point constituent leads to a pre-melt zone in the feed-rod that adversely affects growth stability. Second, constitutional super-cooling (CSC), which was found to lead to dendritic and columnar features in the grain morphology, necessitates slow traveling rates during growth. Both challenges were addressed by modifications to the floating-zone furnace that steepened the temperature gradient at the melt-solid interfaces. Slow growth was also required to counter the effects of CSC. Single crystals with typical dimensions of hundreds of microns have been obtained which possess high quality and are suitable for detailed structural studies.

    更新日期:2017-09-13
  • Thermodynamics and nucleation mechanism of ammonium jarosite in sulfuric acid solution
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-31
    PengFei Liu, YiFei Zhang, Li Wang, ShaoWei You, Jing Bo

    Jarosite process is one of the most widely used methods in removing Fe, but in which the nucleation mechanism of ammonium jarosite has not been reported. Solubilities of the ammonium jarosite crystals under different Fe2(SO4)3 and (NH4)2SO4 concentrations and under different temperatures were measured, and the experiments of induction periods were systematically investigated in different temperatures (348k, 358k and 368k) and H2SO4 concentrations (9g/L, 10.8g/L and 12.6g/L) by reaction crystallization process based on the thermodynamic equilibrium data. According to the model of classical nucleation theory, the interfacial tension and the surface entropy factors in different conditions were calculated as 1.21mJ/m2, 1.85mJ/m2, 1.71 mJ/m2 and 1.51, 1.27, 1.17. The SEM photographs of (H3O, NH4)Fe3(SO4)2(OH)6 approved that the ammonium jarosite crystals were clearly grown by the two-dimensional nucleation mechanism and/or the spiral growth mechanism. But the growth mechanism of (H3O, NH4)Fe3(SO4)2(OH)6 had been determined to be the continuous growth by the surface entropy factor.

    更新日期:2017-09-13
  • Effects of reaction-kinetic parameters on modeling reaction pathways in GaN MOVPE growth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-30
    Hong Zhang, Ran Zuo, Guoyi Zhang

    In the modeling of the reaction-transport process in GaN MOVPE growth, the selections of kinetic parameters (activation energy Ea and pre-exponential factor A) for gas reactions are quite uncertain, which cause uncertainties in both gas reaction path and growth rate. In this study, numerical modeling of the reaction-transport process for GaN MOVPE growth in a vertical rotating disk reactor is conducted with varying kinetic parameters for main reaction paths. By comparisons of the molar concentrations of major Ga-containing species and the growth rates, the effects of kinetic parameters on gas reaction paths are determined. The results show that, depending on the values of the kinetic parameters, the gas reaction path may be dominated either by adduct/amide formation path, or by TMG pyrolysis path, or by both. Although the reaction path varies with different kinetic parameters, the predicted growth rates change only slightly because the total transport rate of Ga-containing species to the substrate changes slightly with reaction paths. This explains why previous authors using different chemical models predicted growth rates close to the experiment values. By varying the pre-exponential factor for the amide trimerization, it is found that the more trimers are formed, the lower the growth rates are than the experimental value, which indicates that trimers are poor growth precursors, because of thermal diffusion effect caused by high temperature gradient. The effective order for the contribution of major species to growth rate is found as: pyrolysis species>amides>trimers. The study also shows that radical reactions have little effect on gas reaction path because of the generation and depletion of H radicals in the chain reactions when NH2 is considered as the end species.

    更新日期:2017-09-13
  • Numerical simulation of the distribution of individual gas bubbles in shaped sapphire crystals
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-24
    A.V. Borodin, V.A. Borodin

    The simulation of the effective density of individual gas bubbles in a two-phase melt, consisting of a liquid and gas bubbles, is performed using the virtual model of the thermal unit. Based on the studies, for the first time the theoretically and experimentally grounded mechanism of individual gas bubbles formation in shaped sapphire is proposed. It is shown that the change of the melt flow pattern in crucible affects greatly the bubble density at the crystallization front, and in the crystal. The obtained results allowed reducing the number of individual gas bubbles in sapphire sheets.

    更新日期:2017-09-13
  • Applying the X-ray diffraction analysis for estimating the height and width of nanorods in low symmetry crystal multiphase materials
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-24
    Ali Mokhtari, Vishtasb Soleimanian, Hamed Aleebrahim Dehkordi, Kamran Dastafkan

    In this work the potential of Rietveld refinement procedure is used to study the shape and size of non-spherical nanocrystallites. The main advantages of this approach are that not only it can successfully extend to all nanomaterials with different crystal symmetries but also it can evaluate the various phases of multiple materials comparing to electron microscopy methods. Therefore, between seven crystal systems, the formulation of monoclinic and hexagonal crystals is developed. This procedure is applied for the mixture of sodium carbonate and zinc oxide nanocrystallites at different fractions of doped gadolinium oxide. It is found that the crystallites of sodium carbonate and zinc oxide have the rod and ellipsoidal shapes, respectively. The microstructure results are compared with the results of scanning electron microscopy imaging. Good agreement is achieved between the results of scanning electron microscopy and Rietveld methods.

    更新日期:2017-09-13
  • Preventing phase separation in MOCVD-grown InAlAs compositionally graded buffer on Silicon substrate using InGaAs interlayers
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-23
    David Kohen, Xuan Sang Nguyen, Riko I. Made, Christopher Heidelberger, Kwang Hong Lee, Kenneth Eng Kian Lee, Eugene A. Fitzgerald

    Compositionally graded InAlAs buffers grown by metal-organic chemical vapor deposition are impaired by phase separation occurring at In content higher than 35%. Phase separation results in rough epilayers with poor crystalline material quality. By introducing low temperature grown InGaAs interlayers in the compositionally graded InAlAs buffer, the surface roughness decreases, allowing a grading of up to In0.60Al0.40As without any phase separation occurring. This composite buffer is applied to fabricate a 200 mm diameter InP-on-Si virtual substrate with a threading dislocation density around 1×108 cm-2.

    更新日期:2017-09-13
  • A multilayer nucleation model for twinning during directional solidification of multi-crystalline silicon
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-23
    H.K. Lin, C.W. Lan

    Twin nucleation is an important phenomenon in the directional solidification of photovoltaic multi-crystalline silicon. Unfortunately, the models proposed so far were not sufficient to explain the small undercooling (<1 K) for twinning observed in the experiments. In this paper, we propose a multilayer nucleation mechanism for twinning during silicon directional solidification. When the nucleus contains more than one layer, the free energy of formation for the nucleus can be reduced. As a result, the critical radius decreases and the twinning probability increases. The required undercooling for twinning based on the present model could be reduced to around 0.4∼0.6 K, which is much more consistent with the experimental observations.

    更新日期:2017-09-13
  • Competition between crystalline and icosahedral order during crystal growth in bimetallic systems.
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-19
    B. Gonzalez, Solene Bechelli, Ilham Essafri, Vincent Piquet, Caroline Desgranges, Jerome Delhommelle

    Using molecular dynamics simulations, we study the crystallization process in Ag6Cu4 and CuAu alloys. By changing the amount of supercooling, we are able to identify the role played by icosahedral order in the crystal growth kinetics. Specifically, the Ag6Cu4 alloy exhibits a slowing down of the growth rate when temperature decreases, as a result of the greater amount of icosahedral order in the liquid. On the other hand, there is much less icosahedral order in the CuAu alloy and, as a result, this system displays the expected behavior of increased growth rates for greater supercooling. Furthermore, by varying the metal used as a substrate for the crystal growth process, we are able to show the major role played by the size mismatch between the atoms of the substrate and the alloy during the polymorph selection process.

    更新日期:2017-09-13
  • Development of longer Nd:LGGG crystal for high power laser application
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-12
    Yanru Yin, Hanlin Tian, Jian Zhang, Wenxiang Mu, Baitao Zhang, Zhitai Jia, Jingliang He, Xutang Tao

    In order to further improve the Nd3+:(LuxGd1-x)3Ga5O12 (Nd:LGGG) crystal performance in high power laser field, a long Nd:LGGG crystal with dimensions of Φ 23×112 mm3 has been grown successfully by the Czochralski (Cz) method for laser rod fabrication. Compared with the normal size LGGG crystals (like 30∼50 mm in length), we overcame several difficulties in the growth of longer ones, including crystal cracking by a large longitudinal temperature gradient, spiral growth by a small radial temperature gradient, and growth instability and even constitutional super cooling by Ga2O3 volatilizing continuously. The doping concentrations of Nd3+ and Lu3+ in the as-grown crystal and the crystal optical quality have been measured. The performance of diode-side-pumped Nd:LGGG rod laser has been preliminarily tested for the first time, simply by replacing the Nd:YAG crystal rod inside a commercial laser module. Under an incident pump power of 160 W, the maximum continuous wave output power of 38 W has been obtained, corresponding to an optical-optical conversion efficiency of 23.8% and a slope efficiency of 40.8%, respectively.

    更新日期:2017-09-13
  • Origin and effective reduction of inversion domains in aluminum nitride grown by a sublimation method
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-12
    Keisuke Shigetoh, Kayo Horibuchi, Daisuke Nakamura

    Owing to the large differences in the chemical properties between Al and N polarities in aluminum nitride (AlN), the choice of the polar direction for crystal growth strongly affects not only the quality but also the shape (facet formation) of the grown crystal. In particular, N-polar (0 0 0 −1) has been considered to be a more preferable direction than Al-polar (0 0 0 1) for sublimation growth because compared to Al-polar (0 0 0 1), N-polar (0 0 0 −1) exhibits better stability at high growth rate (high supersaturation) conditions and enables easier lateral enlargement of the crystal. However, some critical growth conditions induce polarity inversion and hinder stable N-polar growth. Furthermore, the origin of the polarity inversion in AlN growth by the sublimation method is still unclear. To ensure stable N-polar growth without polarity inversion, the formation mechanism of the inversion domain during AlN sublimation growth must be elucidated. Therefore, herein, we demonstrate homoepitaxial growth on an N-polar seed and carefully investigate the obtained crystal that shows polarity inversion. Annular bright-field scanning transmission electron microscopy reveals that polarity is completely converted to the Al polarity via the formation of a 30-nm thick mixed polar layer (MPL) just above the seed. Moreover, three-dimensional atom probe tomography shows the segregation of the oxygen impurities in the MPL with a high concentration of about 3 atom%. Finally, by avoiding the incorporation of oxygen impurity into the crystal at the initial stage of the growth, we demonstrate an effective reduction (seven orders of magnitude) of the inversion domain boundary formation.

    更新日期:2017-09-13
  • A kinetics model for MOCVD deposition of AlN film based on Grove theory
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-12
    Kaiwen Pu, Xianying Dai, Dongming Miao, Shujing Wu, Tianlong Zhao, Yue Hao

    Based on Grove theory, a kinetic model for MOCVD deposition of AlN film was proposed and built in this paper. Physical and chemical processes, e.g., gas phase transport, surface adsorption, surface chemical reactions, as well as the gas phase reactions in boundary layer were analyzed in the kinetic model. Based on this model, the effects of substrate temperature and chamber pressure on the growth rate of AlN film were investigated, as well as the corresponding mechanisms. Meanwhile, the dependences of AlN growth rate and temperature, pressure for three types of reaction pathways were also analyzed. The simulated results provide an important insight into the optimizing of AlN growth with appropriate temperature and pressure in experiment.

    更新日期:2017-09-13
  • Growth of homogeneous Nd:LGGG single crystal plates by edge-defined film-fed growth method
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-10
    Wenxiang Mu, Zhitai Jia, Yanru Yin, Qiangqiang Hu, Yang Li, Xutang Tao

    Device-size Nd3+:(LuxGd1-x)3Ga5O12 (Nd:LGGG) single crystal plates have been grown by edge-defined film-fed growth (EFG) method for the first time. The problems encountered during the crystal growth have been discussed and solved, resulting in a single crystal plate with a length of 180 mm. In particular, the evaporation loss of Ga2O3 composition during the crystal growing has been depressed efficiently by using an Ir lid. The crystal perfection was confirmed by X-ray rocking curve with a FWHM of the 32 arcsec, meaning a high crystalline quality. It was very interesting to find that the distribution of Nd3+ in the crystal grown by EFG method was more homogeneous than that in Cz method, benefitting from the larger segregation coefficient of Nd3+ in EFG method. The thermal conductivity was measured to be 8.1 Wm-1K-1 at room temperature. All the properties showed that the Nd:LGGG crystal plates grown by EFG method were promising for high power laser application.

    更新日期:2017-09-13
  • Fast growth of n-type 4H-SiC bulk crystal by gas-source method
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-08-08
    Norihiro Hoshino, Isaho Kamata, Yuichiro Tokuda, Emi Makino, Takahiro Kanda, Naohiro Sugiyama, Hironari Kuno, Jun Kojima, Hidekazu Tsuchida

    Fast growth of n-type 4H-SiC crystals was attempted using a high-temperature gas-source method. High growth rates exceeding 9 mm/h were archived at a seed temperature of 2550°C, although the formation of macro-step bunching caused doping fluctuation and voids in the grown crystal. We investigated a trade-off between growth-rate enhancement and macro-step formation and how to improve the trade-off. By controlling the growth conditions, the growth of highly nitrogen-doped 4H-SiC crystals without the doping fluctuation and void formation were accomplished under a high growth rate exceeding 3 mm/h, maintaining the density of threading screw dislocations in the same level with the seed crystal. The influence of growth parameters on nitrogen incorporations into grown crystals was also surveyed.

    更新日期:2017-09-13
  • Crystal growth and dislocation etch pits observation of chalcopyrite CdSiP2
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-07-10
    Zhiyu He, Beijun Zhao, Shifu Zhu, Baojun Chen, Wei Huang, Li Lin, Bo Feng

    CdSiP2 is the only crystal that can offer Non-critical Phase Matching (NCPM) for a 1064 nm pumped optical parametric oscillation (OPO) with idler output in the 6 μm range. In this paper, a large, crack-free CdSiP2 single crystal measuring 18 mm in diameter and 65 mm in length was successfully grown by the Vertical Bridgman method (MVB) with an explosion-proof quartz ampoule. The results of lattice parameters, element composition and IR transmittance of the as-grown crystal characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS) and Fourier transformation infrared spectrometer (FTIR) showed the as grown crystal crystallized well and the absorption coefficients at 4878 cm-1 and 2500 cm-1 were 0.14 cm-1 and 0.06 cm-1. Moreover, a new etchant composed of Br2, HCl, HNO3, CH3OH and H2O (1 : 800 : 800 : 400 : 400 in volume ratio) was prepared and the dislocation etch pits on oriented faces of as-grown CdSiP2 crystal were observed for the first time. It is found the etch pits are in rectangular structure on the (101) face, but in trigonal pyramid structure on (312) face. According to the quantities of the etch pits, the average densities of dislocation were evaluated to be 2.28×105/cm2 and 1.4×105/cm2, respectively.

    更新日期:2017-09-13
  • Fabrication of high-quality strain relaxed SiGe(1 1 0) films by controlling defects via ion implantation
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-05-24
    M. Kato, K. Arimoto, J. Yamanaka, K. Nakagawa, K. Sawano

    We investigate effects of ion implantation on strain relaxation of SiGe(1 1 0) layers grown on Si(1 1 0) substrates. Ar+ or Si+ ion implantation is carried out before or after the SiGe growth. It is found that the strain relaxation of the SiGe(1 1 0) film is largely enhanced due to implantation-induced defects both for Ar and Si implantation. Particularly, the sample with Si implantation after the SiGe growth allows large strain relaxation and smaller surface roughness than Ar implantation. As a result, a 50-nm-thick Si0.79Ge0.21 or Si0.77Ge0.23(1 1 0) buffer layer with almost full relaxation and rms surface roughness below 0.5 nm was obtained. It is, therefore, expected that high-mobility strained Si/Ge(1 1 0) channels can be realized on the SiGe(1 1 0) relaxed buffer layers fabricated by Si implantation. It is also demonstrated that the local introduction of the implantation defects allows controlling of lateral strain states and dislocation generation, opening new concepts of engineering of both strain and surface orientation.

    更新日期:2017-09-13
  • Growth of InN/GaN dots on 4H-SiC(0001) 4° off vicinal substrates by molecular beam epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-05-24
    Keisuke Matsuoka, Shuhei Yagi, Hiroyuki Yaguchi

    We have fabricated self-assembled InN dots on GaN using 4H-SiC(0001) vicinal substrates (4° off toward [11–20]). The size and density of InN dots were well controlled by changing the deposition amount and the growth temperature of InN. Atomic force microscope (AFM) observation revealed that the critical thickness of InN for 2D-3D transition was between 0.8 and 1.0 nm. In addition, it was found that the InN dots were preferentially formed at the multistep edges on GaN. Therefore, the preparation of periodic multistep structures on GaN is considered to be an effective way to obtain highly ordered self-assembled InN dot arrays.

    更新日期:2017-09-13
  • Selective area growth of N-polar GaN nanorods by plasma-assisted MBE on micro-cone-patterned c-sapphire substrates
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-05-18
    V.N. Jmerik, N.V. Kuznetsova, D.V. Nechaev, T.V. Shubina, D.A. Kirilenko, S.I. Troshkov, V.Yu. Davydov, A.N. Smirnov, S.V. Ivanov

    The site-controlled selective area growth of N-polar GaN nanorods (NR) was developed by plasma-assisted MBE (PA MBE) on micro-cone-patterned sapphire substrates (µ-CPSS) by using a two-stage growth process. A GaN nucleation layer grown by migration enhanced epitaxy provides the best selectivity for nucleation of NRs on the apexes of 3.5-µm-diameter cones, whereas the subsequent growth of 1-μm-high NRs with a constant diameter of about 100 nm proceeds by standard high-temperature PA MBE at nitrogen-rich conditions. These results are explained by anisotropy of the surface energy for GaN of different polarity and crystal orientation. The InGaN single quantum wells inserted in the GaN NRs grown on the µ-CPSS demonstrate photoluminescence at 510 nm with a spatially periodic variation of its intensity with a period of ∼6 µm equal to that of the substrate patterning profile.

    更新日期:2017-09-13
  • Ultra-low charge and spin noise in self-assembled quantum dots
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-05-10
    Arne Ludwig, Jonathan H. Prechtel, Andreas V. Kuhlmann, Julien Houel, Sascha R. Valentin, Richard J. Warburton, Andreas D. Wieck

    Self-assembled InxGa1−xAs quantum dots (QDs) are promising hosts for spin qubits with excellent coupling to photons. Nuclear spin and charge fluctuations lead to dephasing and limit the applicability of QDs as qubits. We show that charge noise can be minimized by high quality MBE growth of well-designed heterostructures yielding natural optical linewidths down to 1.15 µeV. To minimize the nuclear spin noise, one direction would be to reduce the wave function overlap with the nuclei. We show that this is indeed the case for a single hole spin in a QD that we embedded in the intrinsic region of an n-i-p-diode. For random nuclei, the heavy-hole limit is achieved down to neV energies, equivalent to dephasing times of microseconds.

    更新日期:2017-09-13
  • Up-converted photoluminescence in InAs/GaAs heterostructures
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-05-07
    Yuwei Zhang, Itaru Kamiya

    Up-converted photoluminescence (UPL) in InAs/GaAs heterostructures has been investigated. Relaxation process imposes a great challenge for efficient UPL. It is found that efficient UPL can be detected by the luminescence from InAs/GaAs multi quantum well (MQW), and that the intensity could be enhanced by further improving crystalline quality of GaAs barrier. In addition, choosing proper energy states as intermediate states is another important issue to enhance UPL. We describe how the overall UPL efficiency can be controlled by the epitaxial growth and selection of intermediate states.

    更新日期:2017-09-13
  • Some aspects to the understanding of the droplet epitaxial nano-hole formation
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-05-04
    Ákos Nemcsics

    In this work, the self-assembled GaAs based nano-hole formation prepared by droplet epitaxial technique is discussed. Here, a qualitative explanation is given why thermal solution cannot be observed under droplet edge and can only detected under droplet middle. The thermal etching takes place far from the droplet edge because of its special quantum mechanical state, which causes melting point increase at the droplet edge. Furthermore it is explained, why thermal solution is preferred under the middle of the droplet. Here, we give a lucid interpretation for the nano-hole formation dependence on the arsenic environment. It is evidenced, that the surrounded lobe initiative originates from the remained droplet edge. We give here a qualitative description why we need somewhat ambient arsenic for the process of nano-hole formation. The material transport needs arsenic ambient and not the thermal solution.

    更新日期:2017-09-13
  • Strain and anisotropy effects studied in InAs/GaAs(2 2 1) quantum dashes by Raman spectroscopy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-04-21
    L.I. Espinosa-Vega, E. Eugenio-Lopez, J.M. Gutierrez-Hernandez, A. Yu. Gorbatchev, S. Shimomura, Victor H. Mendez-Garcia

    Quantum dashes were synthesized in the molecular beam epitaxial growth of InAs on GaAs(2 2 1). By changing the arsenic pressure it was possible to obtain highly ordered one-dimensional InAs arrays as demonstrated by autocorrelation function analysis. Polarized Raman spectroscopy was utilized in order to characterize the samples and to estimate the stress at the InAs/GaAs interface as well as the surface anisotropy imposed by the quasi one-dimensional character of the quantum dashes. The most ordered surface, showed the lowest correlation length, and for this sample the Raman spectra exhibits small shift of the GaAs resonance modes indicating likewise small GaAs tensile strain.

    更新日期:2017-09-13
  • Laterally biased structures for room temperature operation of quantum-well infrared photodetectors
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-04-19
    Álvaro Guzmán, Raquel Gargallo-Caballero, Xiang Lü, Holger T. Grahn

    Laterally biased quantum-well infrared photodetectors (LBQWIPs) are expected to exhibit a photoresponse at room temperature. In these devices, the photocurrent is collected by means of two lateral Ohmic contacts on each side of an undoped quantum well (QW), which is coupled by tunneling to another n-doped QW. Photoexcited electrons from the n-doped QW tunnel through to the undoped QW and are swept out via a lateral bias voltage. Up to now, the practical development of these structures has not been yet achieved due to the difficulty of contacting single QWs separated by a few nanometers. In this paper, we report on a viable technology to fabricate LBQWIPs. We present two procedures to contact individual QWs, which are sufficiently close to be coupled by tunneling. The final devices exhibit very low dark-current values and clear infrared absorption peaks at 300 K, in good agreement with the results of numerical simulations. This work demonstrates the practical functionality of the laterally biased structure and paves the way for future developments of room temperature QWIPs.

    更新日期:2017-09-13
  • Nucleation and formation of Au-catalyzed ZnTe nanowires on (0 0 1) GaAs by MBE: From planar to out-of-plane growth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-04-13
    V.V. Volobuev, H. Groiss, A. Halilovic, H. Steiner, A. Khiar, G. Hesser, G. Springholz

    The growth evolution of gold-catalyzed ZnTe nanowire condensates on (0 0 1) GaAs substrates is studied. The samples are obtained by molecular beam epitaxy. The growth of nanowires has been monitored in situ by RHEED and investigated ex-situ by TEM, SEM, XRD. In addition to nanowires sticking out of surface in 〈111〉 direction, formation ZnTe thin film is observed. It is found, that formation of the nanowire condensate occurs in three stages. At the initial stage of growth planar nanowires form and continue to grow in 〈110〉 direction until their intersection occurs. After the intersection, nanowires change the growth direction from planar to out-of-plane. At the final stage of growth in-plane nanowires coalescence forming a thin film. In addition to main reflections from ZnTe nanowires some oriented spots and rings have been observed on RHEED patterns. We attribute these spots to twin formation in nanowires and rings to a presence of disoriented domains in ZnTe film condensates.

    更新日期:2017-09-13
  • Optical spectroscopy analysis of the near surface depletion layer in AlGaAs/GaAs heterostructures grown by MBE
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-04-13
    I.E. Cortes-Mestizo, E. Briones, C.M. Yee-Rendón, L. Zamora Peredo, L.I. Espinosa-Vega, R. Droopad, Victor H. Méndez-García

    In this work the effects of filling the surface energy states in AlGaAs/GaAs heterostructures on the depletion layer are reported. The depletion layer width was varied from 49 to 10 nm as determined by Raman spectroscopy, allowing to discern their effect on the generation of Franz-Keldysh oscillations observed by photoreflectance spectroscopy. It is found that the photoreflectance modulation process of built-in electric fields at surface is negligible when the surface-levels are filled. This work demonstrates the relationship between the surface-states density, the surface states capability of capture carriers and the layer sequence of the heterostructure. These parameters need to be considered in order to get an adequate analysis of the photoreflectance spectrum of heterostructures. It is shown that if a nearly full-filled condition in the available surface energy levels is established, the Franz-Keldysh oscillations produced by the modulation of the built-in electric field intensity disappears as a result of the reduction in the photogenerated carrier density in the photoreflectance measurement.

    更新日期:2017-09-13
  • Effective surface passivation of In0.53Ga0.47As(0 0 1) using molecular beam epitaxy and atomic layer deposited HfO2 – A comparative study
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-04-08
    M. Hong, H.W. Wan, P. Chang, T.D. Lin, Y.H. Chang, W.C. Lee, T.W. Pi, J. Kwo

    Molecular-beam-epitaxy (MBE) and atomic-layer-deposition (ALD) high-κ HfO2 dielectrics have been in-situ deposited on MBE-grown pristine p- and n-In0.53Ga0.47As(0 0 1). The HfO2/In0.53Ga0.47As metal-oxide-semiconductor capacitors (MOSCAPs) from both methods all exhibit excellent capacitance-voltage (C-V) characteristics with true inversion and low leakage current densities. Moreover, interfacial trap densities (Dit’s) with no discernible peaks at the mid-gap were measured using the temperature-dependent conductance method. Both HfO2/InGaAs hetero-structures have exhibited outstanding thermal stabilities to 800 °C.

    更新日期:2017-09-13
  • Characterization of antimonide based material grown by molecular epitaxy on vicinal silicon substrates via a low temperature AlSb nucleation layer
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-04-05
    J.B. Rodriguez, L. Cerutti, G. Patriarche, L. Largeau, K. Madiomanana, E. Tournié

    We report on the characterization of GaSb layers grown on silicon substrates using an AlSb nucleation layer. In particular, we investigate the influence of the AlSb layer thickness when this nucleation layer is grown at low temperature (400 °C). X-ray diffraction techniques, atomic force microscopy and transmission electron microscopy were used to characterize the material properties. We demonstrate that there exists a correlation between the micro-twin density, the surface roughness and the broadening of the ω-scan GaSb peaks. Moreover, the AlSb thickness has a strong influence on the micro-twin density, and must be carefully optimized to improve the GaSb quality.

    更新日期:2017-09-13
  • Growth and characterization of AlInAsSb layers lattice-matched to GaSb
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-04-04
    J. Tournet, Y. Rouillard, E. Tournié

    We report on the growth by solid-source MBE of random-alloy AlxIn1–xAsySb1–y layers lattice-matched to (0 0 1)–GaSb substrates, with xAl ∈ [0.25; 0.75]. The samples quality and morphology were characterized by X-ray diffraction, Nomarski microscopy and atomic force microscopy. Layers grown at 400 °C demonstrated smooth surfaces and no sign of phase decomposition. Samples with xAl ≤ 0.60 demonstrated photoluminescence (PL) at 300 K whereas samples with higher Al content only demonstrated PL at low temperature. Samples grown at 430 °C, in contrast, exhibited PL at low temperature only, whatever their composition. Inferred bandgap energies corroborate the estimation of a non-null quaternary bowing parameter made by Donati, Kaspi and Malloy in Journal of Applied Physics 94 (2003) 5814. Upon annealing, the PL peak energies increased, getting even closer to the theoretical values. These results are in agreement with recently published results on digital AlInAsSb alloys. Our work, which reports the first evidence for PL emission from random-alloy AlInAsSb layers lattice-matched to GaSb, opens the way to their use in optoelectronic devices.

    更新日期:2017-09-13
  • Molecular beam epitaxy and characterization of high Bi content GaSbBi alloys
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-30
    O. Delorme, L. Cerutti, E. Tournié, J.-B. Rodriguez

    The epitaxial growth, structural and optical properties of GaSb1−xBix layers are reported. The incorporation of Bi into GaSb is varied in the 0 < x ⩽ 14% range by varying the growth temperature and V:III BEP ratio. The Bi content and the structural properties were determined by Rutherford backscattering and X-ray diffraction, respectively. The optical properties have been studied by photoluminescence (PL) spectroscopy. The surface morphology was observed by optical and atomic force microscopies. The samples show a smooth, droplet free surface up to 11.4% Bi incorporation. All samples exhibit room temperature PL up to a wavelength of 3.8 μm achieved for 14% Bi incorporation. Finally, these alloys have shown a great thermal stability after several annealing at 450 °C. This work thus presents the highest Bi-content GaSbBi alloys and the first demonstration of room-temperature PL emission from GaSbBi alloys.

    更新日期:2017-09-13
  • MBE growth and characterization of type-II InAs/GaSb superlattices LWIR materials and photodetectors with barrier structures
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-28
    Zhicheng Xu, Jianxin Chen, Fangfang Wang, Yi Zhou, Zhizhong Bai, Jiajia Xu, Qingqing Xu, Chuan Jin, Li He

    In the paper the whole heterojunction structure design process in LWIR type-II InAs/GaSb superlattices (T2SLs) detectors has been presented. The high quality T2SLs materials were grown and the high performance double heterojunction LWIR detectors have been fabricated. In the double heterojunction LWIR detectors a electrons barrier layer and a holes barrier layer were designed and introduced successively, based on the electrical properties measurement and compensation doping of the T2SLs intrinsic material. The processed double heterojunction structure photodiodes had a 100% cutoff wavelength of 12.5 μm at 80 K. The peak current responsivity was 2.5 A/W under zero applied bias, corresponding to a quantum efficiency of 30%. The R0A product at 80 K is 14.5 Ω cm2 which leads to the peak detectivity D∗ of 1.4 × 1011 cm Hz1/2/W for the detector.

    更新日期:2017-09-13
  • Optimization of metamorphic buffers for MBE growth of high quality AlInSb/InSb quantum structures: Suppression of hillock formation
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-27
    Y. Shi, D. Gosselink, K. Gharavi, J. Baugh, Z.R. Wasilewski

    The optimization of metamorphic buffers for InSb/AlInSb QWs grown on GaAs (0 0 1) substrates is presented. With increasing surface offcut angle towards [11¯0] direction, the interaction of spiral growth around threading dislocations (TDs) with the offcut-induced atomic steps leads to a gradual change in the morphology of the AlSb buffer from one dominated by hillocks to that exhibiting near-parallel steps, and finally to a surface with increasing number of localized depressions. With the growth conditions used, the smoothest AlSb surface morphology was obtained for the offcut angles range of 0.8–1.3°. On substrates with 0° offcut, subsequent 3 repeats of Al0.24In0.76Sb/Al0.12In0.88Sb interlayers reduces the TD density of AlSb buffer by a factor of 10, while 70 times reduction in the surface density of TD-related hillocks is observed. The remaining hillocks have rectangular footprint and small facet angles with respect to GaAs (0 0 1) surface: 0.4° towards [11¯0] direction and 0.7° towards [1 1 0] direction. Their triangular-shaped sidewalls with regularly spaced atomic steps show occasional extra step insertion sites, characteristic of TD outcrops. Many of the observed sidewalls are dislocation free and offer atomically smooth areas of up to 1 μm2, already suitable for high-quality InSb growth and subsequent top-down fabrication of InSb nanowires. It is proposed that the sidewalls of the remaining hillocks offer local vicinal surfaces with atomic step density optimal for suppression of TD-induced spiral growth, thus providing the important information on the exact substrate offcut needed to achieve large hillock-free and atomically smooth areas on AlInSb metamorphic buffers.

    更新日期:2017-09-13
  • Stencil lithography of superconducting contacts on MBE-grown topological insulator thin films
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-23
    Peter Schüffelgen, Daniel Rosenbach, Elmar Neumann, Martin P. Stehno, Martin Lanius, Jialin Zhao, Meng Wang, Brendan Sheehan, Michael Schmidt, Bo Gao, Alexander Brinkman, Gregor Mussler, Thomas Schäpers, Detlev Grützmacher

    Topological insulator (Bi0.06Sb0.94)2Te3 thin films grown by molecular beam epitaxy have been capped in-situ with a 2 nm Al film to conserve the pristine topological surface states. Subsequently, a shadow mask - structured by means of focus ion beam - was in-situ placed underneath the sample to deposit a thick layer of Al on well-defined microscopically small areas. The 2 nm thin Al layer fully oxidizes after exposure to air and in this way protects the TI surface from degradation. The thick Al layer remains metallic underneath a 3–4 nm thick native oxide layer and therefore serves as (super-) conducting contacts. Superconductor-Topological Insulator-Superconductor junctions with lateral dimensions in the nm range have then been fabricated via an alternative stencil lithography technique. Despite the in-situ deposition, transport measurements and transmission electron microscope analysis indicate a low transparency, due to an intermixed region at the interface between topological insulator thin film and metallic Al.

    更新日期:2017-09-13
  • GaAs quantum dot molecules filled into droplet etched nanoholes
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-19
    Ch. Heyn, A. Küster, A. Gräfenstein, A. Ungeheuer, A. Graf, W. Hansen

    We fabricate self-aligned vertically stacked GaAs quantum dot molecules (QDMs) by filling of self-assembled nanoholes in AlGaAs. The tunable nanoholes are created using local droplet etching (LDE) combining conventional molecular beam epitaxy with self-assembled, lithography-free patterning. The optical emission from single, strain-free QDMs shows clear excitonic features with linewidths below 150 µeV after optimizations of the fabrication process. This allows investigations of the coupling among the individual dots forming a QDM. In electric fields oriented along the axis of the QDM, luminescence emission from direct and indirect transitions can be clearly distinguished. Furthermore, an anti-crossing behaviour demonstrates inter-dot coupling in the QDM.

    更新日期:2017-09-13
  • Self-assembly of vertically aligned quantum ring-dot structure by Multiple Droplet Epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-16
    Martin Elborg, Takeshi Noda, Takaaki Mano, Takashi Kuroda, Yuanzhao Yao, Yoshiki Sakuma, Kazuaki Sakoda

    We successfully grow vertically aligned quantum ring-dot structures by Multiple Droplet Epitaxy technique. The growth is achieved by depositing GaAs quantum rings in a first droplet epitaxy process which are subsequently covered by a thin AlGaAs barrier. In a second droplet epitaxy process, Ga droplets preferentially position in the center indentation of the ring as well as attached to the edge of the ring in [11¯0] direction. By designing the ring geometry, full selectivity for the center position of the ring is achieved where we crystallize the droplets into quantum dots. The geometry of the ring and dot as well as barrier layer can be controlled in separate growth steps. This technique offers great potential for creating complex quantum molecules for novel quantum information technologies.

    更新日期:2017-09-13
  • Ab initio-based approach to novel behavior in semiconductor hetero-epitaxial growth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-10
    Tomonori Ito, Toru Akiyama, Kohji Nakamura

    Novel behavior in semiconductor hetero-epitaxial growth such as InAs/GaAs is systematically investigated using ab initio-based approach incorporating temperature T and beam equivalent pressure p. The calculated In adsorption-desorption boundary curve elucidates that In atoms can adsorb on the InAs(1 1 1)A-(2 × 2) with In-vacancy wetting layer (WL) surface with simultaneous As adsorption similarly to homo-epitaxial growth. On the InAs(0 0 1)-(2×4)α2 WL surface, however, In atoms hardly adsorb on the (0 0 1) WL in contrast with In adsorption on homo-epitaxial surface without strain. These results suggest that strain accumulated in the WL is not significant for the hetero-epitaxial growth on the InAs(1 1 1)A but strongly affects the growth process on the InAs(0 0 1) at the initial growth stage. It is also found that the InAs(0 0 1)-(2 × 3) WL surface fully covered by As dimers is unstable while the (n × 3) surfaces (n = 4, 6, and 8) with (n − 1) dimers and one missing dimer is more stable at the conventional molecular beam epitaxial growth conditions. It should be noted that In atoms are incorporated through In-As dimer formation with As desorption below InAs coverage θ ∼ 0.9 monolayer (ML) on the (n × 3) surfaces. This suggests that the growth dose not proceed at θ > 0.9 ML without strain relaxation on the InAs/GaAs(0 0 1).

    更新日期:2017-09-13
  • InGaAsBi materials grown by gas source molecular beam epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-10
    Likun Ai, Shuxing Zhou, Ming Qi, Anhuai Xu, Shumin Wang

    In this work, the In1−yGayAs1−xBix epilayers were optimized and grown successfully by V90 gas source molecular beam epitaxy (GSMBE). The effect of using an In0.53Ga0.47As buffer layer on the crystalline quality of In1−yGayAs1−xBix epilayers were investigated. With the buffer layer preparation, the surface RMS roughness value of 0.251 nm, a maximum electron mobility of 5700 cm2/Vs and a bulk carrier density of 2.9 × 1016 cm3 are achieved for the In1−yGayAs1−xBix epilayer with the Bi content up to 3.1%.

    更新日期:2017-09-13
  • Light emission enhancement from Ge quantum dots with phosphorous δ-doped neighboring confinement structures
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-09
    K. Sawano, T. Nakama, K. Mizutani, N. Harada, X. Xu, T. Maruizumi

    Room-temperature photoluminescence intensity from Germanium (Ge) quantum dots (QDs) is highly enhanced by the Phosphorous (P) δ-doping at Ge QDs/Si interfaces since stronger confinements of electrons at the interfaces can be realized by the doping. Suppression of surface segregation of the doped P atoms, which is essential for the δ-doping with a sharp profile, is realized by the control of growth temperatures of Ge QDs and spacer-Si layers after P doping. It is, therefore, concluded that higher efficiency light emitting devices can be realized based on Ge QDs with optimal n-type doping and growth conditions.

    更新日期:2017-09-13
  • Improvement in surface morphology of GaSb buffer layer by two-step high and low temperature growth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-08
    Shigekazu Okumura, Shuichi Tomabechi, Ryo Suzuki, Yusuke Matsukura, Koji Tsunoda, Jun-ichi Kon, Hironori Nishino

    The surface morphology of GaSb was investigated by changing growth conditions such as thermal oxide desorption temperature, growth temperature, and growth step by solid source molecular beam epitaxy. At high temperature growth, the pits caused by the thermal oxide desorption remained in the GaSb buffer layer surface, while the surface was sufficiently flattened. At low temperature growth, the pits disappeared, while the surface was not enough flattened even in the case of step-flow mode growth. Since the pits disappeared at lower growth temperature regardless of the growth mode, this behavior might be explained by the Ga migration length depending on the growth temperature. By applying two-step high/low temperature growth, where both growth steps proceed in step-flow mode, flat, a pit-free GaSb buffer surface could be obtained.

    更新日期:2017-09-13
  • Effect of substrate temperature on self-assisted GaAs nanowires grown by Molecular Beam Epitaxy on GaAs (111)B substrates without SiO2 layer
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-08
    Samatcha Vorathamrong, Somchai Ratanathammaphan, Somsak Panyakeow, Piyasan Praserthdam, Chiraporn Tongyam

    In this work, we demonstrate a self-assisted VLS growth of GaAs nanowires directly on GaAs (111)B substrates without assistance of SiO2 layer. We believe that with this technique, we can overcome some inherent problems that usually occur in conventional self-assisted VLS growth and simplify the process. Moreover, to study the effect of substrate temperature, each nanowire sample was fabricated at the different temperature from 400 °C to 600 °C using Molecular Beam Epitaxy (MBE) technique. Surface morphology, elemental composition, and crystal structure of nanowire samples were characterized by Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDX), and X-ray Diffraction Analysis (XRD) respectively.

    更新日期:2017-09-13
  • CdTe layer structures for X-ray and gamma-ray detection directly grown on the Medipix readout-chip by MBE
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-03-01
    A. Vogt, S. Schütt, K. Frei, M. Fiederle

    This work investigates the potential of CdTe semiconducting layers used for radiation detection directly deposited on the Medipix readout-chip by MBE. Due to the high Z-number of CdTe and the low electron-hole pair creation energy a thin layer suffices for satisfying photon absorption. The deposition takes place in a modified MBE system enabling growth rates up to 10 µm/h while the UHV conditions allow the required high purity for detector applications. CdTe sensor layers deposited on silicon substrates show resistivities up to 5.8 × 108 Ω cm and a preferred (1 1 1) orientation. However, the resistivity increases with higher growth temperature and the orientation gets more random. Additionally, the deposition of a back contact layer sequence in one process simplifies the complex production of an efficient contact on CdTe with aligned work functions. UPS measurements verify a decrease of the work function of 0.62 eV induced by Te doping of the CdTe.

    更新日期:2017-09-13
  • Analysis of dark currents and deep level traps in InP- and GaAs-based In0.83Ga0.17As photodetectors
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-02-28
    X.Y. Chen, Y.G. Zhang, Y. Gu, X.L. Ji, S.P. Xi, B. Du, Y.J. Ma, W.Y. Ji, Y.H. Shi, A.Z. Li

    InP- and GaAs-based metamorphic In0.83Ga0.17As photodetectors were grown and investigated. Compared to InP-based photodetector, the dark current of GaAs-based photodetector at room temperature increased 2–3 times but still comparable, whereas at 77 K the dark current increased 2–3 orders. The deep-level transient spectroscopy results reveal that a deep level trap state exists in the GaAs-based photodetector structure. The higher dark current in GaAs-based photodetector at low temperature was mainly ascribed to a deep level trap induced tunneling current. The deep trap centers can also induce non-radiative recombination with smaller thermal active energy in the GaAs-based photodetector structure.

    更新日期:2017-09-13
  • Interfacial characteristics of Y2O3/GaSb(001) grown by molecular beam epitaxy and atomic layer deposition
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-02-27
    Y.H. Lin, K.Y. Lin, W.J. Hsueh, L.B. Young, T.W. Chang, J.I. Chyi, T.W. Pi, J. Kwo, M. Hong

    High quality Y2O3 on GaSb was achieved using both molecular beam epitaxy (MBE) and atomic layer deposition (ALD) with interfacial characteristics studied by in-situ X-ray photoelectron spectroscopy (XPS) and metal-oxide-semiconductor (MOS) electrical measurements. Ga-oxide and stoichiometric Sb-oxides were obtained in the MBE-Y2O3/GaSb and non-stoichiometric Sb2Ox (x<4) was found in the ALD-Y2O3/GaSb according to the XPS spectra. From the capacitance-voltage (CV) measurements, MBE-Y2O3 provides lower interfacial trap density (Dit) grown at elevated temperature of 200°C, while ALD-grown Y2O3 shows smaller hysteresis and higher dielectric constant.

    更新日期:2017-09-13
  • Stacking InAs quantum dots over ErAs semimetal nanoparticles on GaAs (0 0 1) using molecular beam epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-02-27
    Yuanchang Zhang, Kurt G. Eyink, Lawrence Grazulis, Madelyn Hill, Joseph Peoples, Krishnamurthy Mahalingam

    Hybrid nanostructures are known to elicit an enhanced optical response. We study the directed alignment of ErAs metal nanoparticle (NP) and InAs quantum dot (QD) using molecular beam eptaxy (MBE) in a GaAs matrix. Due to high surface free energy caused by the crystal structure difference, overgrowth of an ErAs NP with GaAs forms a depression that condenses subsequent InAs adatoms to form an inverted QD self-aligned to the underlying ErAs NP. The ErAs NP growth, GaAs overgrowth, and InAs QD deposition were carefully controlled and studied with transmission electron microscopy (TEM) and atomic force microscopy (AFM) to investigate their effects on the QD-NP alignment.

    更新日期:2017-09-13
  • Growth rate dependence of boron incorporation into BxGa1−xAs layers
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-02-27
    H. Detz, D. MacFarland, T. Zederbauer, S. Lancaster, A.M. Andrews, W. Schrenk, G. Strasser

    This work provides a comprehensive study of the incorporation behavior of B in growing GaAs under molecular beam epitaxy conditions. Structural characterization of superlattices revealed a strong dependence of the BAs growth rate on the GaAs growth rate used. In general, higher GaAs growth rates lead to a higher apparent BAs growth rate, although lower B cell temperatures showed saturation behavior. Each B cell temperature requires a minimum GaAs growth rate for producing smooth films. The B incorporation into single thick layers was found to be reduced to 75–80% compared to superlattice structures. The p-type carrier densities in 1000 nm thick layers were found to be indirectly proportional to the B content. Furthermore, 500 nm thick BxGa1−xAs layers showed significantly lower carrier concentrations, indicating B segregation on the surface during growth of thicker layers.

    更新日期:2017-09-13
  • Growth of GaP and AlGaP on GaP(1 1 1)B using gas-source molecular-beam-epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-02-22
    J.-B. Barakat, S. Dadgostar, K. Hestroffer, O. Bierwagen, A. Trampert, F. Hatami

    We present an initial study of the influence of the growth parameters on the surface morphology and on the interface quality of homoepitaxial GaP(1 1 1) and heteroepitaxial GaP/AlGaP(1 1 1) grown on GaP(1 1 1)B substrates using Gas-Source Molecular Beam Epitaxy (GSMBE). Three different surface reconstructions are identified in the RHEED patterns during the growth runs. The Root Mean Square (RMS) surface roughness measured post-growth by AFM ranges from 3 to 10 nm over 10 × 10 µm2 areas, for a film thickness of 100–600 nm. The results of 2θ-ω XRD scans on (1 1 1) and (3 1 1) planes reveal a stacking disorder in the AlGaP layer and further XRD phi-scan measurements on GaP (3 1 1) show strong peaks with 3-fold rotational symmetry and additional of 3-fold weak peaks indicating only a negligible fraction of the twinned crystal orientation in the substrate. TEM images of these samples show a smooth interface between the AlGaP layer and GaP substrate, and reveal the presence of a high density of extended defects such as stacking faults, twinning and dislocations lines in AlGaP layer whereas the GaP layer appears as pure Zinc-Blende. Further TEM analysis reveals composition and local strain variations for GaP/AlGaP samples associated with an undulated surface.

    更新日期:2017-09-13
  • Molecular beam epitaxy of strained-layer InAs/GaInSb superlattices for long-wavelength photodetectors
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-02-22
    Mikhail Patrashin, Kouichi Akahane, Norihiko Sekine, Iwao Hosako

    We report on the growth and characterization of strained-layer InAs/Ga1−xInxSb superlattices for long-wavelength photodetectors. The thickness and alloy composition x < 0.4 of the layers were designed to produce narrow superlattice energy gaps of <50 meV for optical absorption in the terahertz spectral range. The structures were grown on GaSb (1 0 0) substrates by solid-source molecular beam epitaxy. The structure and surface quality were analyzed by using X-ray diffraction, scanning transmission electron microscopy, energy-dispersive spectroscopy, and Rutherford backscattering spectroscopy. Transmittance and reflectance spectra were measured to evaluate the optical properties. The characterization results demonstrated the feasibility of the pseudomorphic growth of strained InAs/GaInSb superlattices and their promising optical properties for long-wavelength photodetectors.

    更新日期:2017-09-13
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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