Abstract
A nominally undoped wurtzite ZnO thin film of highly c-axisorientation was successfully grown on (001) silicon by metal-organicchemical vapour deposition, and its photoluminescence was measured as afunction of excitation intensity at room temperature. The ZnO sampleexhibited a strong near band-edge (NBE) line at 379.48 nm (3.267 eV) anda weak broad green band around ~510 nm (2.43 eV), showing a linearand sublinear excitation dependence of the luminescence intensity,respectively. No discernible intensity dependence of lineshape andemission peak was found for the NBE line. On the other hand, the peakenergy of the green luminescence was found to increase nearlylogarithmically with the increasing excitation intensity. The aboveresults clearly indicate that in the ZnO epilayer, the NBE line was dueto an excitonic spontaneous emission, while the mid-gap greenluminescence can be assigned to the tunnel-assisted donor-acceptor pair(DAP) radiative recombination. Moreover, we obtained an energy depthβ~11.74 meV for the potential wells due to the fluctuatingdistribution of the unintentional impurities/defects responsible for thetunnel-assisted DAP emission.
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