Self-diffusion measurements in isotopic heterostructures of undoped and in situ doped ZnO: Zinc vacancy energetics

摘要

It is well established that formation energies of point defects depend on the chemical potential (μ) and Fermi level position (E_F), which is widely used when modeling diffusion phenomena in semiconductors. In return, Arrhenius analysis of self-diffusion can be exploited for the investigation of point defect energetics since self-diffusion is mediated by intrinsic point defects. Specifically, the energetics of Zn vacancies (V_(Zn)) and/or Zn interstitials in ZnO can be potentially revealed via Zn self-diffusion measurements. In this study we have measured Zn self-diffusion varying μ (by shifting from Zn- to O-rich conditions during the sample synthesis) and E_F (by Ga, F, and Cu in situ doping). Corresponding diffusion activation energies were deduced and are discussed in terms of the vacancy diffusion mechanism. This results in an upper limit estimate for the V_(Zn) migration energy of ～1.5eV, and prominent trends for the V_(Zn)) formation energy as a function of μ and E_F are revealed. Concurrently, it is argued that dopant-V_(Zn)) clustering and E_F pinning at deep donor traps should be taken into account when generalizing the interpretation of diffusion data for impurities in ZnO.