The properties of single and double (Ga,In)As-GaAs strained-layer quantum wells embedded in (pin) diodes are studied. These properties are found to be orientation-dependent, mainly due to the existence of a strong internal piezoelectric field in the (Ga,In)As layers when the growth axis is polar. We first calculate how large the influences of the (pin) and piezoelectric field are to produce carrier tunnelling out of the active part of the heterostructure. This enables us to compute the carrier's lifetime in the heterostructures and the corresponding resonance widths. Next, we compare the binding energies of interacting electron and hole pairs in double quantum wells with or without internal piezo electric fields. We show that the exciton binding energy is less sensitive to the piezoelectric field than the oscillator strength. Under photo excitation, many body-effects and bandgap renormalization can be easily produced in strained-layer quantum wells with internal built-in piezo-electric fields. We illuminated at low temperature single and double Ga0.92In0.08As-GaAs strained layer quantum wells grown either along the (001) or (111) direction, and tuned over several decades the densities of photo-injected carriers. The comparison between experimental data and the results of a Hartree calculation including the space charge effects reveals that many body interactions are efficiently photo-induced in the (111)-grown samples. Moreover, we show that the tunnelling of the two lowest-lying heavy-hole levels can be stimulated for moderate carrier densities making such structures promissive in order to realise self electrooptic effect device (SEED) modulators.

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.

We have studied the temperature dependence of the photoluminescence of tellurium-doped ZnS-ZnSe superlattices. By comparing the reflectivity and photoluminescence data, we were able to identify both free exciton recombination and self-trapped exciton band energy split by 90 meV. The behaviour of the photoluminescence with temperature results from trapping versus detrapping effects which are ruled by an activation energy of 80 meV. This behaviour is analysed in the context of a configuration coordinate diagram.

We present a detailed study of the optical properties of short-period ZnS-ZnSe strained-layer superlattices. These superlattices have been grown by metalorganic vapor-phase epitaxy. We show that the photoluminescence exhibits a low-energy tail due to localization of the exciton to interfacial potential fluctuations. A detailed analysis of the electronic structure has been performed using the envelope-function approach to obtain the valence-band and conduction-band envelope functions and band lineups. This was completed by a self-consistent calculation of the exciton binding energies. In this calculation the marginal conduction-band offset deduced from the standard envelope-function calculation is corrected by the electrostatic deformation produced by the presence of a localized hole wave function.

We have grown ZnSe/ZnS superlattices using low pressure MOVPE. The superlattices were grown onto a relaxed ZnSe buffer and were constituted of 45 periods. The well and barrier thicknesses were chosen from the calculation of critical thicknesses for coherent and free standing situations. Following this analysis we have grown samples with individual ZnSe, ZnS thicknesses of 3 to 9 monolayers. The optical properties of the samples were studied using photoluminescence, photoreflectance and reflectivity experiments. The results of the photoluminescence and photoreflectance experiments are consistent with a free standing model of the strain state, and a typical sketch of potential profile, describing the band structure of such superlattices is proposed. The photoluminescence linewidth is analyzed in terms of interface roughness. The asymmetry of the photoluminescence peaks is modelled using a density of state with a low energy exponential tail, due to the competition between radiative recombination and non-radiative recombination mechanisms. In some samples of lower crystalline quality, bound excitons were observed in the near band edge photoluminescence, which we attribute to impurity interdiffusion, which is favoured by crystalline defects.