Electrical properties of ZnO:Ga as a transparent conducting oxide in InGaN based light emitting diodes

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.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.