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

H and D have been implanted into undoped films of GaN heteroepitaxially gro wn on sapphire over a dose range from 5X10(15) to 5X10(17) ions/cm(2). Afte r a 600 degrees C post-implantation anneal, room temperature Fourier-transf orm-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 m odes strongly suggest they are due to hydrogen bonded to nitrogen atoms; th ese atoms are located on the surfaces of seven sided cavities created by th e H implant and thermal anneal cycle and identified by transmission electro n microscopy. Nuclear reaction analyses of isochronally annealed D implante d films indicate that most of the deuterium remains bound within the implan ted layer, and that the major release stage for D occurs near 900 degrees C . By contrast, the N-H (N-D) vibrational modes anneal out in the 750-800 de grees 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 wa lls and IR-inactive H-2 gas within the cavities. (C) 1999 American Institut e of Physics. [S0021-8979(99)06305-7].