Wurtzite GaN epilayers bombarded with a wide range of ion species ͑10 keV 1 H, 40 keV 12 C, 50 keV 16 O, 600 keV 28 Si, 130 keV 63 Cu, 200 keV 107 Ag, 300 keV 197 Au, and 500 keV 209 Bi) are studied by a combination of Rutherford backscattering/channeling ͑RBS/C͒ spectrometry and cross-sectional transmission electron microscopy. Results show that strong dynamic annealing processes lead to a complex dependence of the damage-buildup behavior in GaN on ion species. For room-temperature bombardment with different ion species, bulk disorder, as measured by RBS/C, saturates at some level that is below the random level, and amorphization proceeds layer-by-layer from the GaN surface with increasing ion dose. The saturation level of bulk disorder depends on implant conditions and is much higher for light-ion bombardment than for the heavy-ion irradiation regime. In the case of light ions, when ion doses needed to observe significant lattice disorder in GaN are large (տ10 16 cm Ϫ2 ), chemical effects of implanted species dominate. Such implanted atoms appear to stabilize an amorphous phase in GaN and/or to act as effective traps for ion-beam-generated mobile point defects and enhance damage buildup. In particular, the presence of a large conce ntration of carbon in GaN strongly enhances the accumulation of implantation-produced disorder. For heavier ions, where chemical effects of implanted species seem to be negligible, an increase in the density of collision cascades strongly increases the level of implantation-produced lattice disorder in the bulk as well as the rate of layerby-layer amorphization proceeding from the surface. Such an increase in stable damage and the rate of planar amorphization is attributed to ͑i͒ an increase in the defect clustering efficiency with increasing density of ion-beam-generated defects and/or ͑ii͒ a superlinear dependence of ion-beam-generated defects, which survive cascade quenching, on the density of collision cascades. Physical mechanisms responsible for such a superlinear dependence of ion-beam-generated defects on collision cascade density are considered. Mechanisms of surface and bulk amorphization in GaN are also discussed.

No abstract

No abstract

No abstract

We study structural disorder in GaN bombarded at room temperature with 1.3 keV amu−1 PFn (n = 0, 2 and 4) cluster ions. Results are compared with our previous studies of irradiation with atomic ions of different masses. An algorithm for cascade density calculations that take into account the formation of subcascades is presented. Quantitative analysis of both new and previous data shows that an increase in the cascade density above a certain critical value results in a rapid increase in the rate of planar amorphization and the rate of damage buildup in the crystal bulk. Both such rates increase with decreasing sample temperature. This threshold-like behaviour suggests an important role of nonlinear energy spikes in the formation of stable implantation disorder in GaN. We also discuss the striking difference between cascade density effects in damage buildup in different semiconductors, including GaN, ZnO and Si.

No abstract

We study structural disorder in ZnO bombarded at room temperature with 1.3 keV∕amu atomic P and cluster PFn (n=2 and 4) ions. Rutherford backscattering/channeling spectrometry results show that the density of collision cascades has a negligible effect on the damage buildup in the crystal bulk in the dose range resulting in ∼1.5−15 displacements per atom. Hence, the amount of stable post-implantation disorder in the bulk can be predicted based on ballistic calculations. In contrast, the cascade density affects radiation damage in the near-surface region. An intermediate defect peak between the expected surface and bulk peaks of disorder forms for ion irradiation conditions with dense cascades.

Damage accumulation in wurtzite GaN films bombarded with 0.5 MeV Bi 1 and 1 MeV Bi 2 ions ͑the so-called molecular effect͒ is studied by Rutherford backscattering/channeling spectrometry. Results show that an increase in the density of collision cascades dramatically enhances the level of implantation-produced lattice disorder in GaN. This effect is attributed to ͑i͒ an increase in the defect clustering efficiency with increasing density of ion-beam-generated point defects and/or ͑ii͒ to collective nonlinear energy spike processes. Such a strong influence of the density of collision cascades is important to take into account for a correct estimation of implantation-produced lattice disorder in GaN.