TEMPERATURE EFFECTS IN THE MULTIPHOTON PHOTOEMISSION OF LASER-IRRADIATED ALPHA-SIO2

The effects of the sample temperature on laser induced electron emissi on of alpha-SiO2 is discussed. The sample was irradiated using the thi rd harmonic of a Nd:YAG laser, with pulse durations of 30 ps, at inten sities in the 10(9) W cm-2 range, leading to an electron emission due to multiphoton absorption. We measured both the total photocurrent and the photoelectron energy spectrum for temperatures ranging between ro om temperature and 250-degrees-C. We observed a strong increase of the photocurrent, which is associated with the disappearance of the charg ing effect due to the holes left by the emission. We interpret this as a result of a thermally induced, trapping/detrapping, electron conduc tivity. This interpretation is based on the fact that hole conductivit y is too small to account for our observations and that intrinsic elec tron conductivity does not show the correct temperature behavior. The increase of the photocurrent is, however, mainly due to an increase of the defect creation yield with the temperature. From these observatio ns possible applications to the problem of low energy electron spectro scopy on insulating samples are discussed.