Polycrystallization and surface erosion of amorphous GaN during elevated temperature ion bombardment

The effects of elevated-temperature ion bombardment of wurtzite GaN films preamorphized by ion implantation are studied by Rutherford backscattering/channeling spectrometry and transmission electron microscopy. Amorphous layers annealed in vacuum at 500 degrees C exhibit polycrystallization. Bombardment of amorphous layers with 2 MeV Cu-63(+) ions at elevated temperatures leads to anomalous erosion of GaN (with a sputtering yield of similar to 10(2) at 500 degrees C), rather than to ion-beam-induced epitaxial crystallization. Temperature dependence of the erosion rate suggests that such a large sputtering yield results from a two-step process of (i) thermally- and ion- beam-induced material decomposition and (ii) ion beam erosion of a highly N-deficient near-surface layer of GaN. This study shows that amorphization during ion implantation should be avoided due to the present inability to epitaxially recrystallize amorphous layers in GaN. (C) 2000 American Institute of Physics. [S0021-8979(00)07922-6].