Defects in hydrothermally grown bulk ZnO

Hydrothermally grown bulk ZnO _Tokyo Denpa_ was investigated using junction-capacitance spectroscopy on silver oxide Schottky contacts (barrier height of 1.20 eV, ideality factor of 1.04). Two main shallow defects, T1 and T2, with thermal activation energies of 13 and 52 meV, respectively, were identified. Two closely lying, deep defect levels E3/E3’ at approximately 320 meV below the conduction band were found in higher concentrations (mid-1014 cm−3) than the shallow donors. 4 K photoluminescence showed dominant emission from excitons bound to three neutral donors, aluminum, hydrogen, and an unassigned impurity, with donor binding energies close to the thermal activation energy of T2.