Wurtzite epilayers were bombarded with a wide range of ion species (10keV 1H, 40keV 12C, 50keV 16O, 600keV 28Si, 130keV 63Cu, 200keV 107Ag, 300keV 197Au, 500keV 209Bi) and were studied by using a combination of Rutherford back-scattering/channelling spectrometry and cross-sectional transmission electron microscopy. The results showed that strong dynamic annealing processes led to a complex dependence of the damage build-up behavior upon the ion species. For room-temperature bombardment with various ions, the bulk disorder (as measured by Rutherford back-scattering/channeling) saturated at a level that was below the random level, and amorphization proceeded layer-by-layer from the GaN surface with increasing ion dose. The saturation level of bulk disorder depended upon the implantation conditions and was much higher for light-ion

bombardment than for heavy-ion bombardment. In the case of light ions, where the ion doses which were needed to observe significant lattice disorder were large (greater than 1016/cm2), chemical effects of the implanted species predominated. Such implanted atoms appeared to stabilize an amorphous phase in GaN and/or acted as effective traps for ion-beam generated mobile point defects and enhanced damage build-up. In particular, the presence of a large concentration of C strongly enhanced the accumulation of implantation-produced disorder. In the case of heavier ions, where the chemical effects of implanted species appeared to be negligible, an increase in the density of collision cascades strongly increased the level of implantation-produced lattice disorder in the bulk; as well as the rate of layer-by-layer amorphization which proceeded from the surface. Such an increase in stable damage, and the rate of planar amorphization, was attributed to an increase in the defect clustering efficiency with increasing density of ion-beam generated defects and/or to a super-linear dependence of ion-beam generated defects (which survived cascade quenching) upon the density of collision cascades.

Effect of Ion Species on the Accumulation of Ion-Beam Damage in GaN. S.O.Kucheyev, J.S.Williams, C.Jagadish, J.Zou, G.Li, A.I.Titov: Physical Review B, 2001, 64[3], 35202 (10pp)