Study of carrier recombination at structural defects in InGaN films

Abstract

A series of 100 nm thick InGaN films with Indium content up to 14% has been grown by MOVPE on SiC substrates. Cathodoluminescence (CL) and remote electron beam induced current (REBIC) in the scanning electron microscope have been applied to investigate with high spatial resolution the recombination of carriers at the structural defects present in the films. The observed defects are mainly pinholes formed at the surface. The density of pinholes increases with the In content in the layers, which can be explained by elastic relaxation at pinholes. CL images show the spatial distribution of the emission sites. For pinholes with diameter in the mum range we observe enhanced luminescence around the pinhole and a reduced luminescence at the apex. Pinholes are observed in REBIC images as dark spots occasionally surrounded by a bright halo. The halo spreads over an area larger than the pinhole, with a diameter of about 3-4 mum. Also a cell-like dislocation structure has been observed in some samples in the CL and REBIC images. CL spectra show, as common features of the samples, a complex emission in the blue range and a broad structured band centered around 670 nm. The influence of the inhomogeneous Indium incorporation on the luminescence of the films and of charged defects on the observed REBIC contrast is discussed.