IOP PUBLISHING REPORTS ON PROGRESS IN PHYSICS Rep. Prog. Phys. 72 (2009) 126501 (29pp) doi:10.1088/0034-4885/72/12/126501 Fundamentals of zinc oxide as a semiconductor Anderson Janotti and Chris G Van de Walle Materials Department, University of California, Santa Barbara, CA 93106-5050, USA E-mail:
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[email protected] Received 10 February 2009, in final form 12 July 2009 Published 22 October 2009 Online at stacks.iop.org/RoPP/72/126501 Abstract In the past ten years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO) as a semiconductor. Being initially considered as a substrate for GaN and related alloys, the availability of high-quality large bulk single crystals, the strong luminescence demonstrated in optically pumped lasers and the prospects of gaining control over its electrical conductivity have led a large number of groups to turn their research for electronic and photonic devices to ZnO in its own right. The high electron mobility, high thermal conductivity, wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including transparent thin-film transistors, photodetectors, light-emitting diodes and laser diodes that operate in the blue and ultraviolet region of the spectrum. In spite of the recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. While a number of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type conductivity.