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HL: Fachverband Halbleiterphysik

HL 44: Poster Session I

HL 44.60: Poster

Dienstag, 15. März 2011, 18:00–21:00, P3

Defects in ZnO thin films studied by photo-capacitance measurements — •Robert Karsthof, Matthias Schmidt, Holger v. Wenckstern, Rainer Pickenhain, and Marius Grundmann — Universtity of Leipzig, Institute for Experimental Physics II, Linnéstraße 5, D-04103 Leipzig

In zinc oxide (ZnO) extensive knowledge on localized electronic states in the vicinity of the conduction band edge exists whereas the number of reported hydrogenic acceptor states or deep levels in the midgap region is scarce. One reason is that capacitance spectroscopic methods commonly measure the thermal emission rate of trapped charge carriers. This works well for levels within 1 eV from the respective band edge at experimentally accessible temperatures and measurement times. In this study we investigated electronic states in the midgap and the vicinity of the valence band of pulsed laser deposited ZnO thin films by means of capacitance spectroscopy with additional optical excitation. The samples were thermally annealed in 700 mbar oxygen and nitrogen atmosphere as well as in vacuum at approx. 700 °C. Two states in the vicinity of the valence band have been detected of which at least one is generated by annealing the samples under low oxygen partial pressures. The photo-ionisation cross-section of the latter one was determined. A midgap level with a threshold photo-ionisation energy of approx. 1.7 eV was detected in every investigated sample. Concentration profiles of the investigated traps have been obtained from capacitance-voltage measurements conducted in the dark as well as under monochromatic excitation.