Role of silicon impurities in the trapping of holes in KTiOPO4 crystals

Abstract

Electron paramagnetic resonance (EPR) has been used to characterize a new hole trap in flux-grown KTiOPO4 crystals. This center is formed at room temperature when the crystals are exposed to either 60 kV x rays or a pulsed 355 nm laser beam. Principal g values measured at room temperature are 2.0030, 2.0102, and 2.0320. The intensity of the EPR spectrum is considerably larger in a silicon-doped sample, thus suggesting that the responsible defect consists of a hole trapped on an oxygen ion adjacent to a silicon impurity located on a phosphorus site. Also, a broad optical absorption band peaking near 500 nm has been observed in the irradiated samples. The silicon-associated hole centers thermally decay over a period of several days at room temperature as electrons are released from Ti3+ traps. Analysis of hole-center decay curves obtained at three temperatures (291, 300, and 311 K) has shown that the kinetics of this electron-release process are primarily second order. The activation energy is approximately 0.80 eV and the “frequency” factor is approximately 4.1×109 s−1.