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.

Apparent p‐type conductivity in nonintentionally doped ZnSe layers, grown at high temperature on semi‐insulating GaAs substrates, is investigated by Raman spectroscopy. The microprobe technique provides direct evidence for carrier location on the GaAs side of the structures, close to the interface. Line‐shape analysis of the coupled LO phonon‐plasmon mode for different exciting wavelengths can be achieved, within the model of Hon and Faust [Appl. Phys. 1, 241 (1973)], only when incorporating plasma inhomogeneity. Electronic band bending at the junction in GaAs is deduced from the inferred carrier‐density profile. Changes in Raman spectra under strong illumination are shown to proceed from the flattening of the bands through selective carrier photoinjection.

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)).

We report on a quantitative analysis of the band gap of hexagonal GaN epilayers in terms of the joint contributions;of the actual wurtzite symmetry on the one hand and of residual strain fields on the other hand. This investigation leads to revision of the previous modelings based on quasicubic descriptions of the valence-band physics and gives Delta(1)=10+/-0.1 meV, Delta(2)=6.2+/-0.1 meV, and Delta(3)=5.5+/-0.1 meV. Last we propose a set of deformation potentials for the hexagonal GaN semiconductor.

A series of In0.14Ga0.86As/GaAs quantum well structures have been grown by metal organic chemical vapor deposition (MOCVD). The measured dependence of photoluminescence (PL) energies on well width is compared with calculation. By the energy shift, line width, and intensity change of PL spectroscopy, critical layer thickness has been identified. The critical layer thickness obtained for MOCVD-grown material was found in agreement with theoretical value, but is smaller than material grown by molecular beam epitaxy.

Graded Index Separate Confinement Heterostructures have been grown by MOVPE using (Zn,Cd)Se and ZnSe wide bandgap semiconductors. These structures are composed of a deep Zn1-xCdxSe (x<0.23%) central well embedded between two thick (Zn, Cd)Se graded layers within which the cadmium composition varies from 0 up to 10% on one side of the well, and from 10 down to 0% on the other side. Both carriers and photon confinement occur in such structures making them suitable for blue-green stimulated emission. Reflectance and photoreflectance data, taken at 2K on a series of samples of different designs allowed us to observe excitonic transitions up to the third quantum number. The structures exhibit a strong photoluminescence line due to the recombination of the carriers in the quantum well. The photoluminescence intensity is analyzed as a function of the temperature and displays a strong thermal quenching. This quenching is due to an increase of the non-radiative recombinations through defects at low temperature and to the thermal escape of the carriers above 40-60K. The value of the activation energy for thermal escape shows that this mechanism is unipolar and concerns the heavy holes.

We report the observation of nonlinear optical properties of ZnSe-ZnTe superlattices under photo-injected carriers, at pumped liquid helium temperature. Identification of several transitions measured by transmission on samples grown by metalorganic vapour phase epitaxy and etched away from the GaAs substrate is made in the context of the envelope function approach. This reveals that the conduction to valence band line-ups are type II in these samples. This situation is invoked in order to interpret the efficiency of the exciton screening.