PNNL

Abstract

Zinc oxide (ZnO) has potential for a range of optoelectronic applications. In this work, we studied the defect properties of ZnO nanocrystals, grown by a solid-state pyrolytic reaction method, using IR and electron paramagnetic resonance (EPR) spectroscopy. A series of IR absorption peaks have been observed at liquid-helium temperatures. These transition lines suggest a hydrogenic acceptor with a hole binding energy of ~ 0.4 - 0.5 eV. EPR measurements in the dark showed the well-known donor line at g = 1.96, and a line at g = 2.003, which we attribute to acceptors that involve a zinc vacancy. A line at g = 2.013, only seen after exposure to light, is assigned to nonaxial zinc vacancy-hydrogen complexes. Given the current lack of suitable acceptor dopants in ZnO, vacancy complexes may provide the best route toward p-type conductivity.