Defect-induced excitonic recombination in TixZn1-xO thin films grown by DC-unbalanced magnetron sputtering

We study the effects of Ti doping on the near-band-edge emission (NBE) and defect-related deep-level emission (DLE) of ZnO thin films grown by DC unbalanced magnetron sputtering. DLE in pure ZnO is contributed by zinc and oxygen vacancies (V-Zn+V-O), as revealed by photoluminescence (PL) spectroscopy, current-voltage (I-V) characteristic measurement, and spectroscopic ellipsometry. The reduction in the number of V-Zn states is clearly observed upon Ti doping, resulting in the enhancement of green emission from V-O. Interestingly, the thin film with a Ti concentration of 1 at.% shows a higher excitonic emission. Furthermore, the temperature dependence of PL spectra shows that the enhanced excitonic emission originates from the donor-bound exciton promoted by the Ti dopant and native V-O. This study shows an important role of the defects in controlling the optical and electronic properties of ZnO films for future optoelectronic applications. (C) 2017 The Japan Society of Applied Physics