Deep levels and persistent photoconductivity in GaN thin films

Abstract

Photocurrent decay in GaN thin films was studied in the time span from a few seconds to several days. The persistent photoconductivity (PPC) behavior was observed not only in Mg-doped p-type GaN films but also in undoped n-type GaN films. The photoconductivity spectra and the photocurrent response time were measured using a weak probe light at several times after the samples had been kept in the dark. During the relaxation, the photocurrent due to the subband-gap probe light decreased more than the photocurrent due to the UV probe light. It is suggested that metastable centers at 1.1, 1.40, and 2.04 eV above the valence band edge are responsible for the PPC behavior in Mg-doped GaN, and that Ga vacancy is the candidate for PPC effect in n-type GaN.