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.

The variable stripe length method is used to study optical gain in MOVPE-grown ZnS/GaAs epitaxial layers. Optical gain and spontaneous emission spectra are extracted from experimental results. A net optical gain of about 30 cm−1 under excitation by a XeCl laser having a power density of 100 kW cm−2 is observed at very low temperatures (T < 20 K) and it is rapidly quenched for higher temperatures. Gain is interpreted to be due to stimulated emission from the bound exciton state and from the biexciton ground state towards free exciton levels. The spectral shape of the gain spectrum is well fitted by the sum of these two contributions. Smaller gain at lower photon energies is obtained due to exciton-excition collisions.

We present a joint study of the band offsets and exciton binding energies in Zn1-xCdxSe-ZnSe quantum wells grown by metal-organic vapor-phase epitaxy with cadmium composition ranging up to 22%. The optical-spectroscopy data presented here are the wavelength derivative of the 2-K reflectance. The strained band-gap difference is divided as follows: the heavy-hole valence-band share deduced from the calculation is 32±1%; the remainder is allotted to the electron conduction band. The exciton binding energy has been calculated within the context of two methods: first, we propose a variational calculation using an exciton wave function written as the product of the envelope-function solutions of the square-well problem with a hydrogenlike two-parameter trial function. Second, as the light-hole potential is marginally type I, we lay out a more sophisticated computation based on a self-consistent variational approach that gives both the exciton binding energies and the self-consistent light-hole densities of probability. We compare the full information given by these two approaches.

We present a detailed examination of the optical properties and electronic structure taken from photoreflectance and photoluminescence data collected on a series of short-period ZnS-ZnSe superlattices grown by low pressure metalorganic vapor phase epitaxy. We studied the band offset problem and calculated the exciton binding energy using several variational models. The temperature dependence of the photoluminescence properties of these superlattices was analyzed in the context of a model which includes the influence of the interfacial disorder.

We report here on the study of the optical properties of ZnCdSe-ZnSe quantum structures elaborated by metalorganic chemical vapour deposition (MOCVD). The band structure is experimentally investigated by means of photoluminescence and photoreflectance. We have computed the exciton binding energies for heavy- and light-hole excitons in the context of a self-consistent two-parameter trial function. As a complement, we study the temperature dependence of the photoluminescence intensity under both direct and indirect photoexcitation in graded-index separate confinement heterostructures based on these materials.

High quality MOVPE-grown ZnS/GaAs epilayers are characterized by reflection, transmission and linear photoluminescence (PL) spectroscopy at 2 K. The GaAs substrate of a part of each ZnS layer is removed and the optical properties of as-grown and etched surfaces are compared. The splitting (caused by the thermally induced strain) of the topmost Gamma(8) valence band into the heavy and light-hole subbands (Delta(hl)=4 meV) and the transitions involving exciton ground and excited states are better seen in PL excitation spectra than in ordinary PL spectra. From the analysis of the nonlinear PL and PL excitation spectra, we can conclude the existence of biexcitons with a binding energy of about 10 to 12 meV under an intermediate intensity of excitation (a density of about 2.5x10(16) to 2.5x10(17) e-h excited pairs per cm(3)).