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

Abstract

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.

Disordering and anomalous surface erosion of GaN during ion bombardment at elevated temperatures

“…A similar band of planar defects has been observed in GaN bombarded with 40 keV 12 C ions and with 100, 300, and 2000 keV 197 Au ions at liquid-nitrogen and room temperatures. 6 Therefore, it can be concluded that these planar defects represent defect structures characteristic for ionbombarded GaN.…”

“…12 Indeed, data reported here and in Ref. 12 indicate that GaN crystals with damage levels above some threshold value exhibit very efficient erosion during elevated-temperature ion bombardment.…”

“…Implantation with 300 keV 197 Au ϩ ions was done at 550°C with a beam flux of 3.1ϫ10 12 ϫ10 16 cm Ϫ2 using the ANU 1.7 MV tandem accelerator ͑NEC, 5SDH-4͒. Before implantation, samples were partly masked by a piece of Si.…”

Ion irradiation-induced disordering of semiconductors: defect structures and applications

“…These include a marked loss of nitrogen under some conditions [26], an anomalously high erosion rate under elevated temperature irradiation [30] and a substantial surface expansion under some high dose conditions [31. 32].…”

Si[sup +] Ion Implantation into GaN at Cryogenic Temperatures

“…Generally, Si + is implanted to create highly doped n-type regions with low sheet resistance to improve contact resistance on transistor structures, although other different device structures have benefited by use of ion implantation, including photodetectors and p-n junction diodes. [4][5][6][7][8] Most of the understanding of the types of defects created in GaN by implantation, the thermal stability of these defect structures and resulting changes in the optical and mechanical properties have come through the work of Kucheyev et al 4,[12][13][14][20][21][22][23][24]26,32 A particularly intriguing approach is the use of cold substrate temperatures during Si implantation into GaN to freeze-in the vacancy concentration and thus potentially increase the substitutional, electrically active fraction of the dopant. 4 The literature on implantation damage in GaN indicates very strong recovery of ion-generated defects during ion bombardment even at LN 2 and in contrast to Si or GaAs, GaN is extremely difficult to amorphize by ion bombardment.…”