Optical and structural properties of In-rich InxGa1−xAs epitaxial layers on (1 0 0) InP for SWIR detectors

https://doi.org/10.1016/j.mseb.2020.114769Get rights and content

Highlights

  • Optical and structural investigation of In-rich InGaAs grown on (1 0 0) InP.

  • Effects of temperature and excitation density on the optical properties of InGaAs.

  • Good correlation between results provided by different characterization techniques.

  • Abnormal behavior of the luminescence keys has been observed.

Abstract

In-rich InxGa1−xAs epitaxial layers were grown on InP (1 0 0) substrates by a metalorganic vapor phase epitaxy (MOVPE) technique. The effect of Indium (In) composition on the crystalline quality and optical properties are investigated. High resolution X-ray diffraction (HR-XRD) measurement and Raman scattering spectrum are used to evaluate the crystalline quality, the residual strain and dislocation density property. The number of dislocations in the epitaxial layers is found to increase by increasing the Indium content in order to release the stresses due to the epitaxial clamping. Photoluminescence (PL) measurement is used to characterize the optical properties. At 10 K, PL measurements show that the InGaAs band gap redshifts with the indium content. Moreover, the asymmetry at the low-energy side of the PL peak has been attributed to the presence of localized excitons. In all samples, a blue shift of PL peaks is evidenced by increasing the excitation power density, which is in line with the presence of carrier’s localization and non-idealities in this system. Moreover, the temperature-dependence of the PL peak energy displays an unusual red-blue-red shift (S-shaped) behavior when raising the temperature. These observations can be related to the inhomogeneous distribution of indium which gives rise to the appearance of dislocations and other defects which serve as traps for charge carriers. Interestingly, those highly In-content InxGa1−xAs epitaxial layers show PL emission located between 1637 and 1811 nm (depending on In content) and thus might be suitable for in the design of novel heterostructure devices such as short wave infrared (SWIR) detectors.

Introduction

InGaAs is one of the most important III-V semiconductor materials attracting attention for their applications in remote sensing, environmental monitoring, optical fiber communication etc [1], [2], [3], [4], [5], [6]. Indeed, their bandgap can be engineered in a large range of the infrared spectrum 0.9–3 µm [7] corresponding to the atmospheric transmission window of interest for military, agricultural, scientific and spectroscopic applications [8], [9]. For instance, lnxGa1−xAs (x = 0.53) grown on InP substrate are commercially available and mature photodetectors with cut-off wavelength at 1.7 μm [9]. As a competitor, II-VI HgCdTe-based materials cover the same wavelength range as InGaAs and many commercial devices exist in the market. However, those HgCdTe detectors require efficient cooling while InGaAs detectors do not need any cooling systems since they can already operate efficiently at room temperature [10]. Moreover, the usually used CdZnTe substrates that have near lattice mismatch with HgCdTe have severe drawbacks such as a lack of large area, a high production cost and, more importantly, a difference in thermal expansion coefficient between those substrates and the silicon readout integrated circuit [11]. Actually, the epitaxial growth and especially the heteroepitaxy of semiconductor materials requires suitable substrate materials which are restricted by lattice mismatch limits. Indeed, the presence of dislocations which appear to relax strains in the active heteroepitaxial layer during the growth can be detrimental to optical and electrical device performances [12].

In case of InGaAs, applications in longer wavelength region (>1.7 μm) require to increase the indium content, which in counterpart increases the lattice mismatch between rich indium content InGaAs and InP substrate. For example, the 2.5 μm cut-off wavelength photodetectors In0.83Ga0.17As have a lattice mismatch of about + 2.1% with respect to InP [13]. As a result, many studies have been conducted to improve crystalline and optical quality and surface roughness as well as decrease deep-level defects of highly indium-doped InxGa1−xAs epitaxial layers. In this context, Xiaoli et al. [14] showed that the high dark current is still one of the critical technology issues for extended wavelength InGaAs detectors. The cut-off wavelength ranges from 1.7 μm to 2.4 μm with the rise of Indium composition from 0.53 to 0.78, but concomitantly the dark current increases about four orders of magnitude. The origin of the enhanced dark current is known to be related to lattice-mismatch between the epitaxial layer and the substrate [14]. For InxGa1‐xAs thin films grown on InP, Liang Zhao et al. [15] used transmission electron microscopy to show that the observed surface undulation which is enhanced with the increase of mismatch degree is caused by the accumulation of dislocations. Moreover, the high density of such structural defects (cluster effect) in the InGaAs layer, can generate localized trap states near the band edge [16]. Any localization of carriers in InGaAs structures due to lattice disorder, impurities, composition or layer thickness variation… [17], [18], [19] has an important effect on their dynamics and thus the properties of the material. A better understanding of the consequences of In content in rich concentration x in InxGa1−xAs alloy is therefore crucial prior to its integration into opto-electronic applications. This is the aim of the current paper. The crystalline quality, the residual strain, dislocation density and optical responses of In-rich InxGa1−xAs epitaxial layers are studied here in detail by high-resolution X-ray diffraction (HR-XRD), Raman spectrocopy, power-dependent photoluminescence (PDPL) and temperature-dependent photoluminescence (TDPL) measurements.

Section snippets

Experimental details

The InxGa1‐xAs epitaxial layers of thickness 190 nm with different In contents (sample S1: x = 0.65, sample S2: x = 0.661 and sample S3: x = 0.667) were grown on (1 0 0) InP substrate by Metalorganic Vapor Phase Epitaxy (MOVPE) at 560 °C. The growth rate is about 3 Å per second. High purity hydrogen (H2) and nitrogen (N2) gases are used as the carrier gas in MOVPE system during the growth. Metal organic (MO) TMGa (Trimethylgallium), TMIn (Trimethylindium) and hydride AsH3 (arsine) are used as Ga,

1. Structural characterizations

The HR-XRD spectrum of the three InxGa1−xAs/InP samples versus 2θ is presented in Fig. 1. We have chosen the interval between 61° and 64° where the {0 0 4} Bragg peak is located. In this figure, it is clear that the high-intense sharp peaks were derived from InP substrates and the other peaks from InxGa1−xAs layers. According to the HR-XRD data, InxGa1−xAs peaks are on the left side of InP peak for all samples, which means that the film is under compressive strain resulting in an enhancement of

Conclusion

To sum up, the structural and optical properties of In-rich InxGa1−xAs epitaxial layers grown on (1 0 0) InP structures have been investigated by HR-XRD, Raman and PL spectroscopies.

The effect of different indium contents on the crystalline quality and optical properties was investigated. We have successfully grown epitaxial InxGa1−xAs films with relatively rich indium content of x = 0.667 without using any buffer layer. We have clearly showed that by increasing the lattice mismatch with the

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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