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  Hoffmann, P.; Pettenkofer, C.: Chemical Nature of N-Ions Incorporated into Epitaxial ZnO Films. In: BESSY [Ed.] : Annual Report 2007Berlin, 2008, p. 211-213

Abstract:
Zinc Oxide (ZnO) is a semiconductor material with a wide (3.4eV) and direct band gap. The large exciton binding energy of 60meV leads to tightly-bound excitons and hence to very effi-cient near-band-gap recombination at room temperature and even higher. This makes ZnO a favourable material for use in opto-electronic devices (e.g. LED’s). However, the application of ZnO in opto-electronics is hindered by the lack of a stable p-doping, since ZnO is n-doped by nature. As the source of the native n-doping are discussed O-vacancies, Zn-interstitials, group-III-elements (Al, Ga) [1] or H-incorporation [2]. A potential p-doping has to overcome this native n-doping. For many reasons, nitrogen appears to be the best candidate for p-doping in ZnO [3]: The ionic radii of nitrogen and oxygen are of comparable size [1], N has the low-est ionisation energy of all possible group-V-elements, and it does not form the N-on-Zn an-tisite (NZn). Beside this advantages of N, it’s low solubility in ZnO and several compensation mechanisms have prevented a stable p-doping of ZnO, up to now [1]. Therefore, we report in this work about the chemical nature of the incorporated nitrogen, investigated by means of PES and NEXAFS. The ZnO was grown epitaxial and the nitrogen was introduced via an ion source, either while epitaxial growth or after the growth.