The spatial distribution of luminescence in Si-doped AlGaN epitaxial layers that differ in Al content and Si concentration has been studied by cathodoluminescence (CL) mapping in combination with scanning electron microscopy. The density of surface hillocks increased with decreasing Al content and with increasing Si concentration. The mechanisms giving rise to those hillocks are likely different. The hillocks induced surface roughening, and the compositional fluctuation and local donor-acceptor-pair (DAP) emission at hillock edges in AlGaN epitaxial layers were enhanced irrespective of the origin of the hillocks. The intensity of local DAP emission was related to Si concentration, as well as to hillock density. CL observation revealed that DAP emission areas were present inside the samples and were likely related to dislocations concentrated at hillock edges. Possible candidates for acceptors in the observed DAP emission that are closely related in terms of both Si concentration and hillock edges with large deformations are a V III -Si III complex and Si N , which are unfavorable in ordinary III-nitrides. V C 2014 AIP Publishing LLC.

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.