High pressure phase transition in Cu doped ZnO

Zinc Oxide (ZnO) is a n-type luminescent semiconductor with a direct band gap of 3.37 eV. It is widely used for the fabrication of optoelectronic devices, biochemical sensors and photovoltaic cells. The doping of different elements in ZnO, can change its optical and electronic properties substantially. Earlier studies have shown that doping ZnO nano particles with copper, enhances its physical, chemical and optical properties and also leads to a substantial reduction in the band gap. To understand the effect of doping copper on the wurtzite to rocksalt transition pressure we have carried out high pressure angle dispersive X-ray diffraction (ADXRD) studies on Cu doped ZnO up to 32 GPa. In our study, we observed the wurtzite to rocksalt transition at much lower pressures than the pristine ZnO. In pristine ZnO, the phase transition initiates at 10.1 GPa and is complete at 16.75 GPa, whereas when doped with copper the transformation starts at 6.7 GPa and completes at 9.4 GPa itself. This study indicates that in the doped ZnO the transition barrier between the wurtzite and rocksalt phase decreases, resulting in a considerable decrease of the mixed phase region and stability range of the wurtzite phase. (author)