Growth of Ga2O3 by furnace oxidation of GaN studied by perturbed angular correlations

Ga2O3 is a promising material for use in solar-blind UV-detectors which can be produced efficiently by oxidation of GaN. In this study we focus on the evolution of the oxide layer when GaN is heated in air. The experimental method applied is the perturbed angular correlation (PAC) spectroscopy of gamma-rays emitted by radioactive nuclides, here Cd-111 and Ta-181, whose parent nuclei are ion implanted into films of GaN grown on sapphire. As the emission pattern for nuclei in GaN is clearly distinct from that of nuclei in Ga2O3, the fraction of probe nuclei in the oxide layer can be directly measured and allows to follow the time dependent growth of the oxide on a scale of less than 100 nm. Additional measurements were carried out with the oxidized sample held at fixed temperatures in the temperature range from 19 K to 973 K showing transitions between the hyperfine interactions of Cd-111 in the oxide matrix both at high and low temperatures. A model for these transitions is proposed.