Hydrothermally grown bulk ZnO was investigated using junction-capacitance spectroscopy on silver oxide Schottky contacts (barrier height of 1.20eV, ideality factor of 1.04). Two main shallow defects, T1 and T2, with thermal activation energies of 13 and 52meV, respectively, were identified. Two closely lying, deep defect levels E3/E3’ at approximately 320meV below the conduction band were found in higher concentrations (mid-1014/cm3) than the shallow donors. The 4K photoluminescence showed dominant emission from excitons bound to three neutral donors, Al, H and an unattributed impurity, with donor binding energies close to the thermal activation energy of T2.

Defects in Hydrothermally Grown Bulk ZnO. von Wenckstern, H., Schmidt, H., Grundmann, M., Allen, M.W., Miller, P., Reeves, R.J., Durbin, S.M.: Applied Physics Letters, 2007, 91[2], 022913