Characterization of ZnSe epitaxial layers by four-wave mixing experiments

Four-wave mixing experiments in two- and in three-beam configurations have been performed at room temperature on ZnSe layers grown by two different techniques: high quality ZnSe layers grown on a GaAs (001) substrate by low-pressure metal-organic vapour phase epitaxy and pulsed laser deposited ZnSe layers on GaAs (001). The GaAs substrates were first removed by polishing and chemical etching. The linear optical properties of the ZnSe epilayers have been studied by photoluminescence, reflection and transmission measurements, in order to analyse the quality of the samples. The third-order nonlinear susceptibility chi((3)), has been measured by degenerate four-wave mixing in the two-beam configuration near the absorption edge at room temperature. chi((3)) values of 3.4 x 10(-4) acid 1.8 x 10(-4) esu respectively have been obtained at about 2.7 eV close to the band edge of the two types of samples. The dynamics of photocreated free carriers has also been studied in the same samples by four-wave mixing experiments in the three-beam configuration at room temperature. A lifetime T-1 = 720+/-20 ps and an ambipolar diffusion coefficient D-a = 5.0+/-0.3 cm(2) s(-1) have been obtained for metal-organic vapour phase epilayers and compared with previously published results. The carrier recombination in the laser-deposited samples has been shown to be much faster, probably due to their higher concentration of crystalline defects. For all the samples studied, the homogeneous dephasing time T-2 was found to be shorter (< 2 ps) than the temporal resolution of our experimental set-up.