Electrical properties of ZnO grown by metalorganic vapour phase epitaxy

ZnO is a wide band gap semiconductor which is a good candidate for the next generation of visible and ultraviolet optoelectronic devices. The electrical properties of thin film ZnO grown on sapphire by metalorganic vapour phase epitaxy (MOVPE) were investigated in this thesis. Hall measurements were performed to determine the electrical properties of the ZnO layers. Films were found to be n-type in all cases with residual carrier densities in the range 5×1017 to 2×1018 cm-3. The addition of In dopant did not result in a significant increase in n-doping despite a large In concentration determined by secondary ion mass spectrometry and low temperature photoluminescence spectroscopy. Temperature dependent Hall measurements showed carrier freeze-out with an activation energy of ~30 meV which is attributed to native donors. No significant change in activation energy was observed for In doping, consistent with poor activation of the In impurities. These data indicate that under the present conditions, In primarily incorporates as an electrically inactive phase. Thermally deposited Al Ohmic contacts were developed, having a sheet resistance of