Identification of silicon as the dominant hole trap in YVO4 crystals

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) have been used to characterize the dominant hole trap in undoped Czochralski-grown yttrium-orthovanadate (YVO4) crystals. A silicon impurity, present inadvertently, replaces a vanadium ion and allows a hole to be trapped on one of the four adjacent oxygen ions. The unpaired spin resides in an oxygen p orbital oriented perpendicular to the plane defined by the silicon ion, the electron-deficient oxygen, and the two yttrium ions nearest the oxygen. Principal values of the g matrix (2.0033, 2.0090, and 2.0771) were obtained from EPR data taken at 15 K. Direct verification of the participation of silicon was obtained from ENDOR data taken at 12 K. We have found that this trapped-hole center appeared in large concentrations in all of our Czochralski-grown YVO4 crystals that were exposed to ionizing radiation (i.e., x rays or an ultraviolet laser beam) while the crystal was at 77 K. Interestingly, a small concentration of this trapped-hole center was present in some as-grown YVO4 crystals before exposure to ionizing radiation. (C) 2002 American Institute of Physics.