Abstract
The diffusion behavior of arsenic (As) and gallium (Ga) atoms from semi-insulating GaAs (SI-GaAs) into ZnO films upon post-growth annealing vis-à-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 ºC and 700 ºC 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 ºC 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 ºC, 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.
Highlights
Zinc Oxide (ZnO) has become one of the most emerging and promising materials in semiconductor research since last couple of years
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
ZnO thin films, grown on SI-GaAs showed p-type conductivity after post-growth annealing at 600 ◦C and 700 ◦C, whereas the conductivity was reverted back to n-type in samples annealed at 800 ◦C
Summary
Zinc Oxide (ZnO) has become one of the most emerging and promising materials in semiconductor research since last couple of years. In this perspective, we have investigated (i) the identity of the acceptor complex which facilitates the p-type conductivity, (ii) the behavior of both As- and Ga-diffusion in ZnO from GaAs substrates on thermal annealing, and (iii) the location of As and Ga in the ZnO lattice so that from the identification of the defect states in the band gap, the doping behavior could be predicted. We have investigated (i) the identity of the acceptor complex which facilitates the p-type conductivity, (ii) the behavior of both As- and Ga-diffusion in ZnO from GaAs substrates on thermal annealing, and (iii) the location of As and Ga in the ZnO lattice so that from the identification of the defect states in the band gap, the doping behavior could be predicted This will help in understanding the role of As- and Ga-diffusion in the (charge) compensation in ZnO and thereby the type conversion in it, as is widely reported
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