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Effect of Oxygen Ion Implantation in Gallium Nitride W. Jiang,(a,b) W. J. Weber,(b,c) and S. Thevuthasan Supported by Office of Basic Energy Sciences. (a) Postdoctoral Research Fellow. (b) EMSL User. (c) Environmental and Health Sciences Division. The n-type GaN single-crystal films (2.0-m m thick) used in the present investigation were obtained from Epitronics and were epitaxially grown by MOVPE on a sapphire substrate. The ion implantation and in-situ RBS/C measurements on these <0001>-oriented films were performed using the accelerator facilities at the EMSL. The 600 keV O+ ions were implanted at an angle of 60° relative to the surface normal in order to produce shallow damage that could be readily measured by 2 MeV helium ion channeling. Specimens were implanted at low temperatures (190 K or 210 K) to various fluences ranging from 4.8 ´  1017 to 5.0 ´  1020 O+/m2, equivalent to 0.026 to 26.7 displacements per atom (dpa) at the depth of ~0.2 m m (damage peak position). The implanted areas (1.2 ´  1.2 mm2) had uniform ion distributions. Ion fluence integration was achieved by applying a positive voltage of 300 V to the target in order to prevent secondary electron emissions. A sequence of in-situ RBS/C spectra for GaN/Al2O3 irradiated at 210 K to various O+ fluences is shown in Figure 9.18, along with random-equivalent and virgin (unirradiated) spectra. The backscattering yields are monotonically increasing with ion fluence up to 3.0 ´  1020 O+/m2. At the highest fluence (5.0 ´  1020 O+/m2), the damage accumulation appears to have saturated. The result suggests that full amorphization cannot be achieved at this temperature under O+ irradiation. At lower temperatures, irradiation with heavy ions results in complete amorphization of GaN (Tan et al. 1996; Liu et al. 1998). Figure 9.18. A sequence of in-situ 2.0 MeV He+ RBS/C spectra for <0001> GaN (2–m m thick) irradiated with 600 keV O+ ions (60° off surface normal) at 210 K to different ion fluences (ions/m2). The dependence of relative Ga atomic disorder on dose (dpa) is shown in Figure 9.19. Full amorphization corresponds to 1.0 on the vertical scale. The 190 and 210 K irradiations performed at different times show no difference within the experimental error and give reproducible results. The maximum relative Ga disorder at saturation under the experimental conditions is ~60% at the damage peak. The solid line in Figure 9.20 is a sigmoidal fit to the data. Figure 9.19. Relative Ga disorder as a function of ion dose (dpa) for GaN irradiated with 600 keV O+ at 210 and 190 K. Figure 9.20. Relative disorder on the Ga sublattice at damage peak as a function of annealing temperature for various ion fluences (O+/m2) at 210 K. The profiles of relative disorder on the Ga sublattice were determined based on a linear dechanneling approximation. The measured damage profiles at low ion fluences are in reasonable agreement with the profiles calculated by SRIM-97. At higher ion fluences, the damage profile appears to shift to greater depths. Isochronal annealing for 20 minutes at different intervals from room temperature to 970 K was used to follow the damage recovery processes. After each isochronal annealing step, a channeling measurement along the <0001> direction was performed in situ at a temperature below the annealing temperature to insure the annealing process was quenched. The results of isochronal thermal annealing (20-min) are shown in Figure 9.20, where four ion fluences have been chosen as examples. In general, no significant annealing effects occurred up to 970 K in any of the irradiated samples, which covered the full range of atomic disorder in this study. References Liu, C., B. Mensching, M. Zeitler, K. Volz, and B. Rauschenbach, Phys. Rev. B 57, 2530 (1998). Tan, H. H., J. S. Williams, J. Zou, D. J. H. Cockayne, S. J. Pearton, and R. A. Stall, Appl. Phys. Lett. 69, 2364 (1996). William R. Wiley Environmental Molecular Sciences Laboratory Feedback: webmaster@emsl.pnl.gov Revised: June 12, 2001 Security & Privacy PNNL-13147