Cathodoluminescence studies of threading dislocations in InGaN/GaN as a function of electron irradiation dose

Abstract

Cathodoluminescence (CL) studies have been carried out on a 30 nm GaN/1.5 nmIn0.28Ga0.72N/(0001) GaN single quantum well (SQW) structure in a field emission scanning electron microscope at voltages <5 kV and temperatures down to 8 K. A direct comparison of CL maps with transmission electron microscope studies carried out on back-thinned samples showed that the QW emission was reduced close to defects identified as “V-shaped” pits and around threading edge-type dislocations. Extended area CL spectra showed progressive blueshifting in the QW emission from around 460 to about 445 nm as the electron dose increased. This blueshift, which could be reversed by exposure to UV light, was accompanied by degradation in the spatial resolution of QW CL maps consistent with an increase in the carrier diffusion length from 200 to 330 nm. It is proposed that these effects can be explained by filling of the trap states in the vicinity of the quantum well by free carriers generated during irradiation.