AFM and temperature-dependent photoluminescence studies of the degree of localization induced by quantum-dot like states in InGaN single quantum well light emitting diodes grown by MOCVD on (0 0 0 1) sapphire

Abstract

In this work, we investigate the surface morphology and temperature-dependent photoluminescence of InGaN/GaN single quantum well light-emitting diodes grown by metal organic chemical vapor deposition on (0 0 0 1) sapphire and their correlation with the degree of localization induced by quantum-dot-like states in these structures. By varying the growth parameters and based on atomic force microscopy and 300 K photoluminescence findings, a high density of quantum-dot-like states was achieved in our InGaN structures. More specifically, atomic force microscopy reveals 10–50 nm diameter dots with a density in the range of 2–30×10 9 cm 2. At the same time, the room temperature photoluminescence signal shows at least a 10× intensity increase compared to similar structures without the dots. Temperature-dependent photoluminescence spectra display the anomalous “S-shaped” behavior of the PL energy peak for the structures where the quantum-dot-like states are present. Concurrently, a change in the temperature range of the photoluminescence emission that outlines the “S-shape” is observed for samples with different dot density and size. A strong correlation of the “S-shape” lower inflection point with the degree of localization induced by the presence of quantum-dot-like states is proposed. Applying the principles and observations discussed, a thermally robust 465 nm single quantum well light-emitting diode with an unpackaged chip-level output power in the 5.5–6.0 mW range and forward voltage <3.2 V at 20 mA was recently achieved.