Structural and optical properties of polar and non-polar ZnO films grown by MOVPE

Polar and non-polar ZnO films were synthesized on different planecuts (a-, c- and R-planes) of Al2O3 substrates by metal-organic vapor-phase epitaxy. Polar ZnO films were obtained on c- and a-Al2O3 substrates whereas non-polar ZnO films were obtained on R-Al2O3 substrates. In spite of generally better crystalline quality and optical properties of polar ZnO films, there are two characteristic photoluminescence peaks detected in the non-polar material only. The peaks (at 3.048 and 2.966 eV) are tentatively assigned to electron transitions involving zinc vacancy and oxygen interstitial defect states, respectively.