Deep centres in ZnO

Abstract

In ZnO, deep centres such as the transition metal ions Cu, Fe, Co, etc., deep acceptors such as Li and Na as well as intrinsic defects such as the cation and anion vacancies are the origin of light emissions in various regions of the visible and infrared spectral range. One example of luminescence in the visible spectral range was already presented in Fig. 7.1. In Fig. 9.1 other examples of deep centre related emissions are given, which are often found in bulk and epitaxially grown ZnO or in nano rods. The presentation of optical properties of various deep centres is complemented by data from electron paramagnetic resonance (EPR). It proceeds from the green and yellow emission bands and their interpretation to transition metals. From the intrinsic defects, the oxygen vacancy is discussed since many years as one of the origins of a broad emission band in the green spectral range. Other intrinsic defects are frequently discussed in recent literature, but the discussion is still rather controversial and the experimental findings on which the various assignments are based are frequently much less elaborate compared, for example, to transition metals. Therefore, no individual section is devoted to these complexes but some information is given, for example, at the end of Sect 5.1.