Abstract
The results of the study on threading dislocation density (TDD) in homo- and heteroepitaxial GaSb-based structures (metamorphic layers, material grown by applying interfacial misfit array (IMF) and complex structures) deposited using molecular beam epitaxy are presented. Three measurement techniques were considered: high-resolution x-ray diffraction (HRXRD), etch pit density (EPD), and counting tapers on images obtained using atomic force microscopy (AFM). Additionally, high-resolution transmission electron microscopy (HRTEM) was used for selected samples. The density of dislocations determined using these methods varied, e.g., for IMF-GaSb/GaAs sample, were 6.5 × 108 cm−2, 2.2 × 106 cm−2, and 4.1 × 107 cm−2 obtained using the HRXRD, EPD, and AFM techniques, respectively. Thus, the value of TDD should be provided together with information about the measurement method. Nevertheless, the absolute value of TDD is not as essential as the credibility of the technique used for optimizing material growth. By testing material groups with known parameters, we established which techniques can be used for examining the dislocation density in GaSb-based structures.
Highlights
The performance of optoelectronic devices is, among other things, affected by the presence of defects in semiconductor structures, e.g., point and extended ones
Three approaches based on high-resolution x-ray diffraction (HRXRD) measurements, the counting of etch pits, and tapers on scanning electron microscopy (SEM) and atomic force microscopy (AFM) images were used
The HRXRD approach utilizing the angular broadening of rocking curves gave dependencies of dislocation density (DD) closer to the data obtained using the other two techniques than the one using the strain broadening of RC
Summary
The performance of optoelectronic devices is, among other things, affected by the presence of defects in semiconductor structures, e.g., point (antisites and interstitials) and extended (dislocations) ones. The latter are formed mainly in the lattice-mismatched heterostructures. The large lattice mismatch of about 7.8% between GaSb epilayer and GaAs substrate leads to relaxation of the lattice strain by the generation of 60◦ misfit dislocations These can propagate through the entire material structure, reaching a density in the order of 109 cm−2 [4]. Optimization of the growth of complex lattice-mismatched heterostructures requires a fast, simple, and reliable technique for estimation of Crystals 2020, 10, 1074; doi:10.3390/cryst10121074 www.mdpi.com/journal/crystals
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