Impacts of dislocation bending and impurity incorporation on the local cathodoluminescence spectra of GaN grown by ammonothermal method

Abstract

Spatially resolved cathodoluminescence (CL) spectra of GaN films grown on freestanding GaN seeds via fluid transport by the ammonothermal method were correlated with the microstructure and growth polarity. The spectral line shape of local CL was nearly position independent for a 4-μm-thick N-polar film exhibiting featureless morphology. The spectra exclusively exhibited a broad near-band-edge (NBE) free carrier recombination emission with Burstein-Moss shift. Conversely, CL spectra at 100K of a 5-μm-thick Ga-polar film having (101¯1) and (101¯2) facets with ridges originating from central pits exhibited a NBE peak at 3.444eV and emission bands at 3.27, 2.92, and 2.22eV, all of which showed rich intensity contrasts in the CL mapping images. The NBE peak intensity was remarkably enhanced at crests of the ridges, where the density of threading dislocations (TDs) having edge components was greatly reduced by the dislocation bending. The results encourage one to grow low TD density GaN wafers by slicing thick crystals grown by the ammonothermal method.