Dislocation and indium droplet related emission inhomogeneities in InGaN LEDs

Abstract

This report classifies emission inhomogeneities that manifest in InGaN quantum well blue light-emitting diodes grown by plasma-assisted molecular beam epitaxy on free-standing GaN substrates. By a combination of spatially resolved electroluminescence and cathodoluminescence measurements, atomic force microscopy, scanning electron microscopy and hot wet potassium hydroxide etching, the identified inhomogeneities are found to fall in four categories. Labeled here as type I through IV, they are distinguishable by their size, density, energy, intensity, radiative and electronic characteristics and chemical etch pits which correlates them with dislocations. Type I exhibits a blueshift of about 120 meV for the InGaN quantum well emission attributed to a perturbation of the active region, which is related to indium droplets that form on the surface in the metal-rich InGaN growth condition. Specifically, we attribute the blueshift to a decreased growth rate of and indium incorporation in the InGaN quantum wells underneath the droplet which is postulated to be the result of reduced incorporated N species due to increased N2 formation. The location of droplets are correlated with mixed type dislocations for type I defects. Types II through IV are due to screw dislocations, edge dislocations, and dislocation bunching, respectively, and form dark spots due to leakage current and nonradiative recombination.

InGaN-based green micro-LED efficiency enhancement by hydrogen passivation of the p-GaN sidewall

“…These low-scale inhomogeneities in spatial EL distribution are related to the thermal degradation of InGaN QW 27) and propagating dislocation in LED's active region and p-side. 28,29) The EL observation for the pixel with applied hydrogen passivation, as shown in Fig. 3(b), has a dimmed frame around the pixel perimeter.…”

Low voltage drop AlGaN UV-A laser structures with transparent tunnel junctions and optimized quantum wells

“…As the growth was done under metal rich conditions without any interruption, gallium droplets were formed which are also correlated with dislocation densities. The active region underneath the droplets induces an increase in aluminum composition of the barriers and reduction in QW thickness, yielding a blue shift [41]. The region with the droplet (blue circle) shows a blue shift in PL with respect to the off-droplet (red circle) region, as confirmed by the cathodoluminescent (CL) spectra measured in the sample with 2.4 nm QW as shown in figure 1(c).…”

Harnessing III-Nitride Built-In Field in Multi-Quantum Well LEDs

“…The dark circular spots are accompanied by screw and edge dislocations, which serve as nonradiative recombination centers and can contribute to the leakage current. More comprehensive descriptions of the defects observed in LEDs grown by PA-MBE can be found in ref . For subsequent investigations, devices with full square metal contacts (Figure j–m) are used as they offer more reliable and reproducible results.…”