Dechanneling analysis of disorder in (100) gallium arsenide

The methods of transmission electron microscopy and high resolution RBS/channeling with MeV energy He⁺ ions have been applied to a study of defect structures in ion implanted (100) GaAs. Implant conditions (substrate temperature 102 K, implants of 100 keV Te⁺ to fluences between 4×10¹³ and 2×10¹⁴ cm^-2) and anneal schedule (15 min at 623 K) were chosen to promote the formation of twins in the near-surface region of the epitaxial regrowth layer. TEM diffraction patterns and dark field micrographs from the annealed samples gave evidence for twinning on {111} planes. The residual amorphous layer thickness was estimated to be less than 2 nm for all cases. Rutherford backscattering spectra were recorded for He⁺ ion channeling in the [001] direction and dechanneling characteristics determined for a range of ion beam energies. From the combined analyses a picture emerges of a regrowth layer rich in twins, initially with the 〈221〉 directions of the twins parallel to the 〈001〉 directions of the original crystal, but becoming progressively misoriented towards the surface.