MOCVD growth of thick V-pit-free InGaN films on semi-relaxed InGaN substrates

Abstract

The MOCVD growth of InGaN:Si base layers on a semi-relaxed InGaN substrate, where growth is generally difficult due to the presence of V-pits, is examined. These V-pits can propagate through the crystal, causing severe morphological degradation and significantly reducing material quality for device use. Such V-pits may also be a source of leakage current if they extend from the substrate through p-n junction. A wide range of InGaN growth conditions and their impact on V-pit formation and density are investigated. The use of thin GaN interlayers, carrier gas selection, and V/III ratio are found play a critical role in managing V-pit quantity and size. Finally, high temperature GaN interlayers are implemented, fully eliminating V-pit formation in 1200 nm thick InGaN base layers grown coherently on semi-relaxed InGaN substrates.

InGaN-Based microLED Devices Approaching 1% EQE with Red 609 nm Electroluminescence on Semi-Relaxed Substrates

“…In our previous work, we developed a base layer scheme consisting of a InGaN/GaN buffer/interlayer structure designed to fully eliminate the V-defects and achieve high crystal quality. These base layers employ optimized growth conditions for buffer and interlayer thicknesses, temperatures, V/III ratio, and carrier gasses [17]. This base layer was also designed to match the lattice constant of the substrate, maintaining the relaxed strain state present initially.…”

Realization of III-Nitride c-Plane microLEDs Emitting from 470 to 645 nm on Semi-Relaxed Substrates Enabled by V-Defect-Free Base Layers

“…Since the semi-relaxed InGaN substrates used here have a high density of V-defects, material quality must be significantly improved during the epitaxy to realize robust LED devices. In our previous work, we report on fully eliminating the V-defects in the InGaN base layers originating in the substrates through periodically growing high temperature (HT) GaN interlayers under partial H 2 carrier gas injection in the InGaN base layer, leading to significant structural improvement [18]. This improvement can also be noted in Figure 2, which clearly shows the full elimination of V-defects on the optimized base layer.…”

“…For all samples, the HT GaN interlayers eliminated the pre-existing V-defects and prevented the creation of new ones. The structure and growth conditions of the base layer, as well as study of the V-defect elimination mechanism, are examined in great detail in prior work [18]. Once base layers were grown, we regrew active regions (ARs) consisting of 5 periods of 2.8 nm thick InGaN QWs, 2 nm AlGaN cap layers with 10% Al content, and 10 nm GaN quantum barriers (QBs) consisting of a 4 nm lower temperature (LT) portion and 6 nm higher temperature (HT) portion.…”

“…Additionally, interlayer schemes of GaN layers contained within an InGaN base layer have been reported to reduce other defects, retain 2D step-flow growth, and significantly improve material quality over a single thick InGaN layer [17]. In our previous work, we have explored and developed an InGaN/GaN buffer/interlayer scheme similar to a superlattice (SL) with optimized buffer and interlayer thicknesses, temperatures, V/III ratio, and carrier gasses [18]. These developments significantly improve the crystal quality for the base layer and allow the advantages of the relaxed InGaN substrate to be leveraged into devices.…”

“…We examine the application of these periodic InGaN/GaN base layer structures on relaxed substrates in the growth of µLEDs to enable emission across the entire visible spectra. Employing an InGaN/GaN interlayer structure with high temperature (HT) GaN interlayers, where the elevated temperature has shown to improve Ga surface diffusion and both fill pre-existing V-defects and suppress their subsequent formation [18], we enable working µLED devices with appreciable electroluminescence emission across the visible range. For µLEDs grown on these InGaN/GaN base layers, a significant reduction in the V-defect density and an improvement to crystal quality results in appreciable electroluminescence readily visible even by eye.…”