Electron-nuclear double resonance of the zinc vacancy in ZnGeP2

Abstract

Electron-nuclear double resonance (ENDOR) has been used to identify the singly ionized zinc vacancy (VZn− center) in ZnGeP2. This S=1/2; defect is the dominant paramagnetic acceptor in the material, and it is associated with the absorption from 0.7 to 2.5 μm that limits the use of ZnGeP2 in optical parametric oscillators. The unpaired spin of the VZn− center is shared nearly equally by two phosphorus nuclei adjacent to the vacancy with little overlap of the wave function onto the other two phosphorus neighbors. Angular dependence of the ENDOR spectrum shows that the two primary 31P nuclei have nearly axial hyperfine matrices with unique axes pointing approximately toward the center of the vacancy. The internuclear axis for these two phosphorus makes an angle of 37.8° with the basal plane.