Properties of LT-AlGaN films and HT-GaN films using LT-AlGaN buffer layers grown on (0001) sapphire substrates

Abstract

Low-temperature (LT) Al x Ga1−xN (0.1 < x < 0.8) films, 0.4 μm in thickness, were prepared on (0001) sapphire substrates at 500,∘C by alternate supply of Ga and Al alkyls and ammonia (NH3). Al composition in the solid phase was identified based on the shift of the (0002) Bragg angle of X-ray diffraction. A series of high temperature (HT) GaN films, 1.0 μm in thickness, were also grown at 1000,∘C on the LT-Al x Ga1−xN coated (0001) sapphire substrates with buffer layer thickness ranging from 7.5 to 20 nm. It was found that the optimized LT-Al x Ga1−xN buffer layer thickness decreases linearly with the Al-content. As-grown HT-GaN films having LT-LT-Al0.43Ga0.57N buffer layers show smooth surface based on optical microscopic (OM) observations. Transmission electron microscopy (TEM) confirms the mono-crystalline nature of the HT-GaN films. The quenched near band-edge photoluminescence (PL) emissions and an apparent yellow luminescence of the HT-GaN films are attributed to the LT-Al x Ga1−xN buffer layer induced mosaic microstructure and bonding defects in the films.