Dislocation and Indium Droplet Related Emission Inhomogeneities in InGaN LEDs

TL;DR

This study classifies emission inhomogeneities in InGaN LEDs grown by plasma-assisted molecular beam epitaxy, linking them to dislocations and indium droplets, and analyzes their characteristics and origins.

Contribution

It provides a detailed classification of emission inhomogeneities in InGaN LEDs and correlates them with specific dislocation types and indium droplet formation.

Findings

Type I inhomogeneities are linked to indium droplets and cause a blueshift in emission.

Different inhomogeneity types are associated with specific dislocation structures.

Inhomogeneities result in leakage current and nonradiative recombination, affecting LED performance.

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 KOH 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 N$_{2}$ 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.