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°C exhibit polycrystallization. Bombardment of amorphous layers with 2 MeV ⁶³Cu⁺ ions at elevated temperatures leads to anomalous erosion of GaN (with a sputtering yield of ∼10² at 500°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.