CATHODOLUMINESCENCE OF MOVPE-GROWN GAN LAYER ON ALPHA-AL2O3

Cathodoluminescence (CL) of a Zn-doped GaN layer and an undoped GaN layer grown by metalorganic vapor phase epitaxy (MOVPE) on an α-Al2O3 (0001) (C-face) substrate has been investigated in relation to the microcrystalline structure of GaN. Three typical bands in the CL spectra at room temperature (RT) are as follows: (a) ∼ 365 nm, edge emission in the undoped layer, (b) ∼ 425 nm, violet emission in the Zn-doped layer, and (c) ∼ 485 nm blue emission in the Zn-doped layer. The emission (a) is weak in rough-surface areas and grain boundary areas whose crystalline quality is poor, and such areas include many nonradiative recombination centers. The intensity of the emission (b) is very strong in the rough-surface area (the off-facet area), while it is weak in the smooth-surface area (the facet area of the C-face). The nonuniformity of the emission (b) could be attributed to a local change in the Zn concentration. The intensity of the emission (b) is increased by electron beam irradiation, especially in the off-facet area. The CL image (c) is rather insensitive to the surface morphology, and it is very uniform in the smooth-surface area. © 1990.