Nonpolar Growth of GaN Films on Polar Sapphire Substrate Using Pulsed Laser Deposition: Investigation of Substrate Temperature Variation on the Quality of Films

The growth of GaN films along nonpolar crystallographic planes, especially s-plane, on c-Al2O3 substrate using pulsed laser deposition (PLD) is reported. The role of substrate temperature variation on the structural and morphological properties along this plane is investigated using different techniques. The degree of crystallinity, surface roughness, etc. associated with films are observed to depend strongly on deposition conditions, for example, substrate temperature kept during deposition. Micro-Raman investigations reveal the presence of an unexpected phonon mode, E-1(LO), in the spectra for films deposited at high temperature where prominent crystal growth is observed. The presence of the particular phonon mode observed herewith is due to the nonpolar growth of GaN crystals as well as high density of defects and/or plasmon coupling present in the films. Strong near-band-edge emission in the photoluminescence spectra for all specimens shows moderate optical properties of the films. Elemental analysis using X-ray photoelectron spectra technique confirms the formation of GaN phase for all specimens.