HYDROGEN DESORPTION AND AMMONIA ADSORPTION ON POLYCRYSTALLINE GAN SURFACES

We have studied the D-2 desorption and NH3 adsorption on polycrystalli ne GaN surfaces using time-of-flight detection of recoiled H+ and D+ i ons. Two surface deuterium states characterized by different thermal s tability are identified. Rate analysis for isothermal D-2 desorption i s performed near 250 degrees C, which we attribute to desorption from Ga sites. We assign the higher temperature D-2 desorption state decomp osing near 500 degrees C to desorption from N sites. Both clean and D- terminated GaN surfaces are quite reactive towards NH3 adsorption. We observed that H/D exchange during NH3 exposure occurs rapidly at room temperature.