Implantation of GaN with transition metals such as Fe has attracted significant research interest in the recent years. This interest has been stimulated by the possibilities to create highly resistive layers in GaN by Fe implantation. Resistance of such layers are more than eight orders of magnitude higher than that of unimplanted material, and reveals excellent thermal stability up to 600 C [1]. Moreover, Fe doped GaN is a potential diluted magnetic semiconductor with a Curie temperature above room temperature [2]. However, it is also necessary to anneal the implantation-induced intrinsic defects. Ion beam-induced processes in GaN have been found to be very complicated and different from those occurring in other semiconductors, indicating strong dynamic annealing processes and significant influence of the surface on defect accumulation [3].
The wurtzite undoped GaN epilayers were grown on sapphire (0001) substrates by MOCVD. Implantation with 50-325 keV Fe ions was done at room temperature in the dose range of 1e15 – 1e17 ions/cm2. After implantation some samples were annealed. Elemental depth profiles and damage build-up were analysed by Time-of-Flight Elastic Recoil Detection Analysis and Rutherford backscattering and channeling technique, respectively.
Results show that for all ion energies the damage in the bulk moves deeper and exhibit saturation with increasing ion fluence. Furthermore, significant stoichiometric changes and material decomposition occurs in GaN for high dose Fe implantation. For the low ion doses (up to 3e15 cm-2) the measured implantation profiles of Fe in the as-implanted samples are in good agreement with simulations using TRIM code. However, for higher ion doses we observe enhanced Fe concentration closer to the surface, which increases as the ion dose increases. The influence of implantation conditions and annealing on damage build-up and Fe redistribution is reported and the possible mechanisms of Fe redistribution closer to the surface with ion dose increasing are discussed.
1. X.A. Cao et al., J. Appl. Phys. 87 (2000) 1091.
2. N. Theodoropoulou et al., Appl. Phys. Lett. 79 (2001) 3452.
3. S.O. Kucheyev, J.S. Williams, S.J. Pearton, Mater. Sci. Eng. R. 33 (2001) 51. |