DIRECT OBSERVATION OF ULTRAVIOLET-LASER INDUCED PHOTOCURRENT IN OXYGEN-DEFICIENT SILICA AND GERMANOSILICATE GLASSES

UV laser induced inonization of silicon oxygen deficient centers (SODC ) in silica glasses and germanium oxygen deficient centers (GODC) in g ermanosilicate glasses has been studied by direct displacement photocu rrent measurements. For both SODC and GODC the two-photon (two-step) n ature of photoionization has been established. The cross sections of t ransitions from first excited to upper (ionizable) states were estimat ed as sigma(12)=6x10(-18) cm(2) for SODC and (0.5-1.0) x10(-19) cm(2) for GODC. The effect of pulse-to-pulse degradation of the photocurrent signal caused by the screening effect is applied to estimate the life times and ranges of the free carriers. The conclusion was drawn, that ionized SODC and GODC play the key role for free charge trapping. (C) 1996 American Institute of Physics.