Observing relaxation in device quality InGaN templates by TEM techniques

Abstract

Device quality InGaN templates are synthesized using the semibulk (SB) approach. The approach maintains the film's 2D growth and avoids the formation of indium-metal inclusions. The strain relaxation processes of the grown InxGa1−xN templates are accompanied by variations in the indium content (x) and lattice parameters (a and c) across the InGaN template's thickness as the residual strain is continuously decreasing. This strain and lattice parameters' variation creates difficulties in applying standard x-ray Diffraction (XRD) and Reciprocal Space mapping (RSM) techniques to estimate the residual strain and the degree of the elastic strain relaxation. We used high-resolution High-angle annular dark-field scanning transmission electron microscopy and Energy-dispersive x-ray spectroscopy (EDS) to monitor the variations of the indium content, lattice parameters, and strain relaxation across the growing InxGa1−xN templates. We show that strain relaxation takes place by V-pit defect formation. Some of these V-pits are refilled by the GaN interlayers in the InxGa1−xN SB templates, while others propagate to the template surface. We present an alternative approach combining photoluminescence (PL) and EDS for estimating the degree of strain relaxation in these InxGa1−xN templates. The values obtained for the degree of relaxation estimated from TEM studies and PL measurements are within reasonable agreement in this study. Device quality InxGa1−xN templates with x ∼ 0.08, with a degree of relaxation higher than 70%, are achieved.

Full InGaN red light emitting diodes

“…for the growth of thick InGaN layer on GaN template [25,26]. Then, the active zone was implemented with 5x In y Ga 1-y N/In x Ga 1-x N multiple quantum wells (MQWs) with average well and barrier widths of 2.3 nm and 6 nm, respectively.…”

“…While many trials have been realized to get a relaxed InGaN buffer layer either from a GaN template (GaN buffer layer on sapphire substrate) or a sapphire substrate, no results with high crystalline quality have been demonstrated yet [19][20][21][22][23][24]. However, M. Abdelhamid et al have recently demonstrated the possibility to get an In 0.08 Ga 0.92 N buffer layer almost fully relaxed on a GaN template with a good material quality by using the semi-bulk technique [25,26]. The electrochemical porosification of the GaN layer beneath the InGaN buffer seems also promising [27].…”

Recent progress in red light-emitting diodes by III-nitride materials

“…This approach maintains smooth surfaces and is acceptable for further epitaxial growth. Semi-bulk structures are favorable for producing [68], Copyright (2020), with permission of AIP Publishing.…”

Thermodynamic Origin of High Efficiency in Long-Wavelength InGaN-Based LEDs on Si Substrates

“…Eldred et al reported that the InGaN QWs grown on periodic InGaN structures had a large red-shift of 12−35 nm, implying the improvement of crystal quality due to the reduction of compressive strain. 21 more, theoretical studies of In incorporation and surface segregation processes have been carried out by Duff et al They found that the considerably reduced growth window due to compressive strain could be widened by growing on latticematched In 0.25 Ga 0.75 N underlying layers. 23 Most of these studies show that the relaxed underlying layers reduce the compressive strain and thus improve the performance of InGaN QWs.…”