Donors and defects characterization in ZnO by luminescence techniques
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ZnO has attracted great interest for the past decade as it is a very promising material for semiconductor device applications. It has a direct band gap of 3.34eV, large exciton binding energy of 60meV and same wurtzite structure as GaN. Various forms of ZnO- bulk, thin film, powder, nanowire and etc.- are studied for different potential applications. While ZnO may be a promising candidate for a wide range of future applications, the lack of understanding and control of intrinsic defects in ZnO has been a main obstacle in ZnO application. Its properties remain a subject of controversy, and prior measurements of the donor ionization energy in ZnO samples have, in fact, shown inconsistent results in terms of the measured energies due to the many species in ZnO that may act as donors.In this work, thermal luminescence spectroscopy is applied on ZnO bulk and thin films. Three hydrogen-related donors were characterized with ionization energies of 36, 47, and 55 meV and measurements provide evidence for the presence of two potential emission centers for the green luminescence in ZnO that are associated with both O vacancies and Zn vacancy related defects. X ray luminescence spectroscopy also confirms that green emission of ZnO is oxygen vacancy related.