Microstructure and Formation Mechanism of V-Defects in the InGaN/GaN Multiple Quantum Wells with a High In Content
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Microstructure and Formation Mechanism of V-defects in the InGaN/GaN Multiple Quantum Wells with a High in Content H. Wang+1) , Q. Tan+∗ , X. He+ + Academy
of Electronic Information and Electrical Engineering, Xiangnan University, 423000 Chenzhou, China
∗ Institute
of Physics and Information Science, Hunan Normal University, 410081 Changsha, China Submitted 2 June 2020 Resubmitted 19 June 2020 Accepted 19 June 2020
In the growth of InGaN/GaN multi-quantum well (MQW) by metal organic chemical vapor deposition (MOCVD), V-defects have been observed and investigated. From cross-sectional transmission electron microscopy, we found that all V-defects are not always connected with threading dislocations (TD) at their bottom. By increasing the indium composition in the Inx Ga1−x N well layer, many V defects are generated from the stacking mismatch boundaries. The formation mechanism of these defects has been discussed in terms of stress induced by lattice mismatch and reduced In incorporation on the {10¯ 11} planes in comparison to the (0001) surface. The V-defect is correlated with the localized excitonic recombination centers that give rise to a long-wavelength shoulder in photoluminescence (PL). The InGaN/GaN multi-quantum well (MQW) grown on the {10¯ 11} faceted sidewalls of the V-defects gave much lower emission energies than those of the c-plane multi-quantum well (MQW). DOI: 10.1134/S0021364020150035
Introduction. InGaN/GaN heterostructures and multi-quantum well (MQW) structures have a wide range of applications such as the active layers in GaNbased light-emitting diodes [1] as it is possible to tune the optical band gap from visible to ultraviolet spectral range by controlling the In composition [2]. However, the initial GaN layer is usually grown on a sapphire substrate, and the high lattice mismatch between substrate and epilayer leads to highly defective material with high densities of threading dislocations (TD). It is usually accepted that the high defect density results in poor optical property and shorter device lifetime [3]. Also, these defects affect the structural and optical quality of the active layer composed of the InGaN/GaN MQW structure [4]. In order to eliminate these defects, it is essential to understand their structures and their formation mechanisms. The strain between the InGaN wells and the GaN barriers in the InGaN/GaN MQW increases with increasing In composition, which results in a change in the structural properties, including structural defects, such as dislocations, stacking faults, voids, etc. [5]. The so-called V-defects have been frequently observed in the InGaN/GaN MQW [6–8]. These defects have a hexagonal inverted pyramidal shape with {10¯ 11} walls and are limited by a hexagon in the basal plane. The origin of 1) e-mail:
these defects and the role they play on the optical emission are still not clear though there are some studies focused on this issue [4, 6, 9]. Recently, Shiojiri et al. [10] have discussed the formation mechanism of V defects taking into account the growth k
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