Identification of electron and hole traps in KH2PO4 crystals

Electron paramagnetic resonance (EPR) has been used to characterize a hole trap and several electron traps in single crystals of potassium dihydrogen phosphate (KH2PO4 or KDP). The paramagnetic charge states of these centers are produced by ionizing radiation (e.g., x rays or a 266 nm beam from a pu lsed Nd:YAG laser) and are stable for days and even weeks at room temperatu re. One center consists of a hole trapped on an oxygen ion adjacent to a si licon impurity located on a phosphorus site. This defect has a small, but e asily observed, hyperfine interaction with the adjacent substitutional prot on. The other centers are formed when an electron is trapped at an oxygen v acancy. These latter defects are best described as (PO3)(2-) molecular ions , where the primary phosphorus nucleus is responsible for a large hyperfine splitting (500-800 G in magnitude). Five EPR spectra representing variatio ns of these oxygen vacancy centers are observed, with the differences being attributed to the relative position of a nearby cation vacancy, either a m issing proton or potassium. An angular study of the EPR spectra, conducted at room temperature, provided principal values and principal directions for the g matrices and hyperfine matrices for the hole center and two of the e lectron centers. (C) 2001 American Institute of Physics.