A study of the film growth environment in pulsed laser deposition of gallium nitride

Abstract

This thesis describes a study of the deposition requirements for growth of stoichiometric GaN thin films using pulsed laser deposition. Growth has been carried out using either ceramic GaN or metal (solid and liquid) Ga targets in molecular nitrogen and nitrogen plasma discharge background gases. The potential advantages of using a liquid target for film growth were considered, as were the problems associated with incongruent material transfer from target to film in ns ablation of GaN. The effect of laser fluence and background gas pressure on the stoichiometry of the films was monitored using an optical reflectometry technique and a model to extract the free gallium fraction in the films. The expansion dynamics of the laser-produced plasma were studied using Langmuir ion probes, in the time-of-flight mode, which allowed the ion energy distribution in an inertial (high vacuum) expansion to be measured. This technique was also used to map the ion energy reduction with increasing distance from the target in a relatively high (~0.1 m bar) N2 background gas pressure.