High performance InAs/InAsSb Type-II superlattice mid-wavelength infrared photodetectors with double barrier
Introduction
Lower size, weight, and power (SWaP) configurations have become important requirements for mid-wavelength infrared (MWIR) photodetectors. Achieving high operating temperature (HOT) single element detector or imager is a feasible solution for this [1]. Sb-based type-II superlattice (T2SL) is one class of materials which has the potential to realize these objectives [2], [3]. In the past decades, T2SL material system has become a growing area of research interest for the development of high performance MWIR photodetectors [4], [5]. This material system has many advantages over other materials, such as the great flexibility of bandgap engineering, uniform materials and cutoff wavelengths across the wafer, lower band-to-band tunneling due to larger electron effective masses, Auger recombination suppression and mature III-V growth and processing technologies. InAs/Ga(In)Sb superlattices are the most studied member of the T2SL family. However, recent reports have shown that InAs/Ga(In)Sb T2SL is limited by a low minority carrier lifetimes [6], [7]. Also, complicated interfaces with large lattice mismatch such as InSb, GaAs or InGaSb between InAs and GaSb layers induce defects and harm the carrier lifetime. With gallium being the suspected origin of defects in GaSb, another T2SL material known as InAs/InAsSb T2SL, has been proposed as another alternative [8]. InAs/InAsSb T2SL, which doesn’t contain gallium has been reported to have significantly longer carrier lifetime [9], [10], [11]. In addition, InAs/InAsSb T2SL has relatively simple interface structure with only one changing element (antimony), which promises a better controllability in epitaxial growth. Based on these advantages, InAs/InAsSb T2SL based photodetectors have become the subject of extensive research recently [12], [13], [14]. Although the InAs/InAsSb T2SL material system has show great potential and has made rapid improvements, it is still facing many challenges. One of them is reducing the dark current of the photodetectors to increase the specific detectivity (D*), which is the main figure of merit for photodetectors that combines both optical and electrical performance. Diffusion, generation-recombination (G-R) and tunneling are the three major causes of dark current in T2SL photodetectors. The diffusion current is a fundamental mechanism in a diode structure. And the generation-recombination (G-R) and band-to-band tunneling occur in the depletion region of the p-n junction. The idea of heterostructure was first discussed by H. Kroemer in the 1950s and has gained a lot of attention from the semiconductor world [15]. In the field of infrared detectors, the use of heterostructure design has shown promising results in suppressing the G-R and tunneling dark current. In recent report, different types of hetero-junction barrier structure were employed to suppress various dark current components such as nBn [16], M−structure [17], and complimentary-barrier infrared detector (CBIRD) [18]. Barrier structure MWIR photodetectors based on InAs/InAsSb T2SL have also been reported [14], [19], [20]. In this work, we propose and demonstrated an InAs/InAsSb T2SL MWIR photodetectors with double barrier structure design for suppressing the G-R current and tunneling current. The introduction of two wide bandgap barrier structures will extend the depletion region of the p-n junction from low bandgap absorption region into the wide bandgao barrier region. This will result in the suppressing of the G-R current and tunneling current.
Section snippets
Device design
Fig. 1(a) shows the schematic diagram of the MWIR double barrier photodetector structure. The MWIR double barrier structure photodetector consists of un-intentionally doped 2.0 µm MWIR InAs/InAs0.5Sb0.5 superlattices, with a composition of 10 monolayers (MLs) of InAs and 2 MLs of InAs0.5Sb0.5, which has theoretical band gap energy of 0.27 eV at 150 K. The top contact is a highly p-type doped GaSb layer. The double barrier consists of two parts, the first barrier is a lightly p-type doped wide
Results and discussion
Fig. 2(a) and (b) shows the AFM image and HR-XRD scan curve of the double barrier photodetector. The sample exhibits a root-mean-square surface roughness of 1.55 Å over a 10 × 10 µm2 area with clear atomic steps. No sign of relaxation or dislocation was observed, indicating a good crystallinity. The HR-XRD scan shows clear and strong satellite peaks, suggesting good periodicity. Both the absorption layer and barrier structure superlattices were strain balanced with the GaSb substrate with
Conclusion
In conclusion, we have reported the design, growth and characterization of a MWIR InAs/InAsSb T2SLs photodetectors with double barrier design. The double barrier structure consists of a lightly p-type doped wide bandgap AlAs0.5Sb0.5/InAs0.5Sb0.5 superlattice barrier and an undoped SWIR barrier to reduce the G-R current by pushing the depletion region into the SWIR barrier. At 150 K, the photodetector exhibits 50% cut-off wavelengths of ~4.50 µm, peak responsivity of 1.42 A/W corresponding to a
Significance
Lower size, weight, and power (SWaP) configurations have become important requirements for mid-wavelength infrared (MWIR) photodetectors. Achieving high operating temperature (HOT) single element detector or imager is a feasible solution for this. In this paper, we present the demonstration of MWIR InAs/InAsSb T2SL photodetectors with a double barrier design. The introduction of the second barrier pushes the depletion region into the wide bandgap barrier region rather than in the narrow bandgap
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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