Damage and microstructure evolution in gallium nitride (GaN) under ion irradiation has been investigated using complementary electron microscopy, secondary ion mass spectrometry and ion beam analysis techniques. Single crystalline GaN samples have been irradiated by 2.0 MeV Au ions to 1.0 × 10¹⁵ and 1.4 × 10¹⁵ cm^-2 at 155 K and 7.3 × 10¹⁵ cm^-2 at 200 K. The irradiation-induced damage has been analyzed by backscattering spectroscopy in a channeling direction (RBS/C). Anomalous damage accumulation behavior is observed, where separate amorphous layers develop from the sample surface and near the damage peak region with increasing irradiation dose. Formation of large nitrogen bubbles with sizes up to 70 nm is observed in the buried amorphous layer, while the surface layer contains small bubbles with diameter of a few nanometers due to significant nitrogen loss from the surface. Volume expansion from 3% to 25% in the irradiated region is suggested by cross sectional transmission electron microscope and RBS/C measurement. The anomalous shape of the Au distributions under three irradiation conditions indicates a significant out-diffusion of Au toward sample surface. The results suggest that nitrogen is retained in the damaged GaN when the crystallinity is preserved. Once the amorphous state is reached in the surface region, GaN starts to decompose and nitrogen escapes from the surface. Furthermore, experimental results show considerable errors in both disorder profile and ion range predicted by the Stopping and Range of Ions in Matter code, indicating a significant overestimation of electronic stopping powers of Au ions in GaN.

Yanwen Zhang*, Pacific Northwest National Laboratory, United States
Zihua Zhu, Pacific Northwest National Laboratory, United States
Manabu Ishimaru, The Institute of Scientific and Industrial Research, Osaka University, Japan
William J. Weber, University of Tennessee, Knoxville and Oak Ridge National Laboratory, United States

*presenting author