We report on the effects of metal organic epitaxy grown GaN templates with different surface morphologies,
achieved under different chamber pressures of 200 and 400 Torr, on the electrical properties of GZO. For as-grown GZO
layers with electron concentration above 1020 cm-3 grown on either 200-Torr p-GaN or 400-Torr p-GaN templates, the
electron concentration is temperature-dependent as opposed to temperature-independence for GZO/a-sapphires, which
demonstrates that the underlying GaN layers affect the GZO electrical properties measured by Hall method. By
annealing in nitrogen environment or by inserting a thick ZnO buffer layer, the effects of the underlying GaN layers on
GZO electrical properties can be eliminated paving the way for accurate determination of electrical properties. All three
annealed GZO layers grown on 200-Torr p-GaN, 400-Torr p-GaN, and a-sapphire, exhibited comparable electron
mobilities (~50 cm2/V·s at 15 K and ~41 cm2/V·s at 300 K) and similar temperature dependences while their electron
concentrations are different (5.1×1020, 7.1×1020, and 9.2×1020 cm-3) due to the substrate-caused differences in GZO
growth mode, structure, etc. By means of simulations, ionized impurity scattering was found to be the dominant
scattering mechanism in the range of 15-330 K for GZO when electron concentration is higher than 5×1020 cm-3.
Although other scattering events caused by defects and structures are weaker than the ionized impurity scattering, the
electrical properties could be still slightly improved by finding more optimized growth conditions to eliminate defects
and/or to improve crystal quality.