Infrared and transmission electron microscopy studies of ion-implanted H in GaN

H and D have been implanted into undoped films of GaN heteroepitaxially grown on sapphire over a dose range from 5×1015 to 5×1017 ions/cm2. After a 600 °C post-implantation anneal, room temperature Fourier-transform-infrared spectroscopy reveals two major local vibrational modes at 3183 cm−1 (2364 cm−1) and 3219 cm−1 (2386 cm−1) for the H (D) material implanted at higher doses. The position and isotope shift (1.35) of these modes strongly suggest they are due to hydrogen bonded to nitrogen atoms; these atoms are located on the surfaces of seven sided cavities created by the H implant and thermal anneal cycle and identified by transmission electron microscopy. Nuclear reaction analyses of isochronally annealed D implanted films indicate that most of the deuterium remains bound within the implanted layer, and that the major release stage for D occurs near 900 °C. By contrast, the N–H (N–D) vibrational modes anneal out in the 750–800 °C temperature range. These findings indicate that the bound H exists in at least two major states, believed to be IR-active N–H on the cavity walls and IR-inactive H2 gas within the cavities.