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

Electron paramagnetic resonance (EPR) has been used to characterize a new h ole trap in flux-grown KTiOPO4 crystals. This center is formed at room temp erature when the crystals are exposed to either 60 kV x rays or a pulsed 35 5 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 lar ger 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-assoc iated hole centers thermally decay over a period of several days at room te mperature as electrons are released from Ti3+ traps. Analysis of hole-cente r decay curves obtained at three temperatures (291, 300, and 311 K) has sho wn 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 X 10(9) s(-1). (C) 1999 American Institute of P hysics. [S0021-8979(99)06402-6].