Cathodoluminescence Study of Optical Inhomogeneity in Si-Doped AlGaN Epitaxial Layers Grown by Low-Pressure Metalorganic Vapor-Phase Epitaxy

Abstract

We have investigated the effects of Si doping on the microscopic optical inhomogeneity of Al0.61Ga0.39N epitaxial layers through the combined use of scanning electron microscopy (SEM) and cathodoluminescence (CL). Hexagonal hillocks and corresponding CL inhomogeneity in AlGaN epitaxial layers were observed in SEM and CL images, respectively, and the density of such structures increased with increasing the Si concentration. CL spectra of Si-doped AlGaN epitaxial layers taken at 80 K showed near-band-edge emission around 4.9 eV and an emission line around 4.4 eV. Monochromatic CL images of Si-doped AlGaN at the detection energy of 4.4 eV appeared selectively at the edges of hexagonal hillocks, indicating selective incorporation of Si atoms into defects at grain boundaries.