Doping nature of group V elements in ZnO single crystals grown from melts at high pressure

ZnO single crystals doped with group-V elements have been grown from melt at high pressure. Dopants were introduced in several forms such as Sb2O3, P, As, Sb and Zn3X2 (X = P, As, Sb) in the high-pressure cell. Systematic studies of morphology were performed using optical microscopy and scanning electron microscopy. Crystal structure and lattice parameters were studied using X-ray diffraction and X-ray crystallography. Crystals exhibited distinct changes of size, shape and color compared to undoped ZnO melt-grown single crystals due to the dopants influence. X-ray photoelectron spectroscopy was used to determine valence states of group-V elements when incorporated in ZnO lattice. Photoluminescence, Raman spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the nature of defects formed as the result of doping. Formation of VZn and VZn-complexes was confirmed and their concentrations were measured. Estimates of the number of VZn per one dopant atom showed that the ratio is noticeably higher than the one suggested for the shallow complex As(P, Sb)Zn-2VZn commonly regarded as responsible for acceptor properties in ZnO.