Tracing fabricated defects with ultrafast photocarrier dynamics in undoped GaN films

Abstract

Defects introduced during the growth of GaN thin films critically affect their electronic and optical performance. Here, optical-pump terahertz-probe (OPTP) spectroscopy was employed to investigate the photocarrier relaxation dynamics in GaN films fabricated using different growth techniques. A clear correlation attributed to differences in defect densities, particularly donor-like trap states, was observed between the photocarrier relaxation behavior probed by OPTP and the carrier mobility measured by the Hall effect. In high-quality films with low defect densities, bimolecular electron–hole recombination leads to pronounced fast decay characteristics in the THz absorption, with a lifetime of several hundred picoseconds. The fast decay component in the OPTP spectra can serve as sensitive indicators of the crystalline quality and defect density, offering a non-contact, nondestructive approach for evaluating the GaN film growth quality.