Anomalous diffusion of Ga and As from semi-insulating GaAs substrate into MOCVD grown ZnO films as a function of annealing temperature and its effect on charge compensation Public Deposited

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  • The diffusion behavior of arsenic (As) and gallium (Ga) atoms from semi-insulating GaAs (SI-GaAs) into ZnO films upon post-growth annealing vis-`a-vis the resulting charge compensation was investigated with the help of x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy. The films, annealed at 600 °C and 700 °C showed p-type conductivity with a hole concentration of 1.1 × 10¹⁸ cm⁻³ and 2.8 × 10¹⁹ cm⁻³ respectively, whereas those annealed at 800 °C showed n-type conductivity with a carrier concentration of 6.5 × 10¹⁶ cm⁻³. It is observed that at lower temperatures, large fraction of As atoms diffused from the SI-GaAs substrates into ZnO and formed acceptor related complex, (AsZₙ–2VZₙ), by substituting Zn atoms (AsZₙ) and thereby creating two zinc vacancies (VZₙ). Thus as-grown ZnO which was supposed to be n-type due to nonstoichiometric nature showed p-type behavior. On further increasing the annealing temperature to 800 °C, Ga atoms diffused more than As atoms and substitute Zn atoms thereby forming shallow donor complex, GaZₙ. Electrons from donor levels then compensate the p-type carriers and the material reverts back to n-type. Thus the conversion of carrier type took place due to charge compensation between the donors and acceptors in ZnO and this compensation is the possible origin of anomalous conduction in wide band gap materials.
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  • Biswas, P., Halder, N. N., Kundu, S., Banerji, P., Shripathi, T., & Gupta, M. (2014). Anomalous diffusion of Ga and As from semi-insulating GaAs substrate into MOCVD grown ZnO films as a function of annealing temperature and its effect on charge compensation. AIP Advances, 4(5), 057108. doi:10.1063/1.4876236
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