OPTICAL NONLINEARITIES AND TWO-PHOTON-GENERATED CARRIER LIFETIMES IN II-VI COMPOUNDS

Abstract

We present a comprehensive investigation on the non-resonant nonlinear optical properties of a direct band-gap II-VI semiconductor compound ZnO. The bound­ electronic and free-carrier optical nonlinearities, and relaxation of two-photon-excited free carriers in ZnO have been determined individually by use of a single-beam Z-scan technique at 532 nm. We have also made the comparison between our experimental measurements and theoretical calculations as well as previous research results, which have shown good agreement. We also report an experimentally simple method for determining photo-excited free-carrier recombination time in semiconductors. This method is based on simulation of the single-beam Z scans with laser pulses of two different widths: 25 ps and 7 ns (FWHM). It is very simple experimentally since it is based on single-beam Z-scan configuration. The lifetime determination should be very effective by simulating Z scans conducted with the pulse duration slightly greater than the carrier lifetime. We demonstrate this method on direct band-gap semiconductor compounds: ZnSe and ZnS.