Conductivity, photoconductivity and optical properties of amorphous GaN films

Abstract

It has been predicted that amorphous GaN has a low density of states in the gap, and therefore has potential as a useful opto-electronic material in the blue-green spectral region. We have synthesised amorphous GaN films on various substrates by ion assisted deposition and investigated the effects of sample preparation conditions on the conducting and optical properties. The room temperature resistivity ρ₀ of stoichiometric (Ga:N of 1:1) films is above 10⁵Ωcm, and these films exhibit a complex form for the temperature dependence of the resistivity. Films having an excess of Ga show a much lower ρ₀. The optical absorption shows a band-gap of 3 eV, with the gap falling below that value when the amorphous network incorporates homopolar (Ga-Ga) bonds. The best films are thus transparent across the visible region with a low density of gap states, undetectable in optical absorption. The photoluminescence spectra obtained from these a-GaN films consist of a broad green light emission peaking at 528 nm. Preliminary photoconductivity measurements show sensitivity in the UV.