Shallow Donors and Compensation in Homoepitaxial ZnO Thin Films

Nominally undoped homoepitaxial ZnO thin films grown with pulsed-laser deposition at various oxygen partial pressures (3 x 10(-4)-0.1 mbar) were investigated with respect to shallow donors and compensation. From x-ray diffraction and photoluminescence studies, a correlation of the oxygen partial pressure and the strain in the samples was found. Capacitance-voltage and thermal admittance measurements, using PtO (x) -Schottky diodes, revealed a higher compensation for increasing oxygen partial pressure. A shallow donor level with a thermal activation energy of similar to 40 meV was observed by thermal admittance spectroscopy. This defect level was attributed to the I-3a transition observed in photoluminescence and commonly assigned to interstitial zinc.