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.

Date Published: 27 February 2012
PDF: 8 pages
Proc. SPIE 8262, Gallium Nitride Materials and Devices VII, 826226 (27 February 2012); doi: 10.1117/12.903930

Published in SPIE Proceedings Vol. 8262:
Gallium Nitride Materials and Devices VII
Jen-Inn Chyi; Yasushi Nanishi; Hadis Morkoç; Joachim Piprek; Euijoon Yoon, Editor(s)