Characterization of defect-related optical absorption in ZnGeP2

A broad optical absorption band with a peak near 1 mu m is present in most single crystals of ZnGeP2. These same crystals have an electron paramagneti c resonance (EPR) signal which has been assigned to singly ionized zinc vac ancies. A direct correlation between the intensity of the optical absorptio n at 1 mu m and the intensity of the EPR signal has been established using a set of ZnGeP2 crystals where this absorption varied widely. These results suggest that the singly ionized zinc vacancy acceptor plays a direct role in the electronic transition(s) responsible for the 1 mu m optical absorpti on. In separate experiments, it was found that illuminating the ZnGeP2 crys tals with a He-Ne laser (632.8 nm) while at temperatures near 25 K produces an increase in the absorption at 1 mu m and an increase in the zinc vacanc y EPR spectrum. These latter results provide further evidence that the abso rption at 1 mu m is associated with the singly ionized zinc vacancy accepto r. (C) 1999 American Institute of Physics. [S0021-8979(99)07624-0].