We discuss the growth of epitaxial structures of (In,Ga)As on GaAs substrates, with elastic and plastic strain, and study the effect of the corresponding built-in strain on the photoluminescence of quantum wells inserted into such buffer layers. In addition, we examine the effect of built-in strain on the full electronic structure of strained-layer quantum wells. Reflectivity data taken at 2 K, where we could measure ground state type I, as well as excited type I and type II transitions, have revealed that a correct description of these heterostructures requires including the effect of the spin-orbit split-off states in the valence band physics as soon as the configuration of the electron-to-light-hole potential profiles switches from type II to type I. We anticipate that this effect should be included for the calculation of threshold cur-rents in quantum well lasers made from such heterostructures.

We show that efficient tunneling of holes can be produced in double quantum wells with built-in piezoelectric fields by the photoscreening of that piezoelectric field. Our observation was made at low temperatures by comparing the behavior of Ga0.92In0.08As-GaAs strained-layer double quantum wells grown along the (111) and (001) directions and tuning the densities of photoinjected carriers over several decades. Interpretation of the experimental data is made by comparison with Hartree calculations including the space charge effects. In addition to this, we also report the observation of many-body interactions at high photocarrier densities.

We have performed a variational calculation of the heavy-hole exciton for (Ga,In)As-GaAs strained-layer quantum wells embedded in p-i-n structures. The calculation has been made for sample growth along both the (001) and (111) directions. We show that the influence of the piezoelectric field may sometimes lead to strong orientation-dependent properties. In particular, when piezoelectric fields are present, the radiative lifetimes of heavy-hole excitons are strongly dependent on the thickness of the (Ga,In)As layer.

We present for the first time a detailed investigation of the growth of ZnTe layers deposited on GaAs substrates by low pressure metalorganic vapour-phase epitaxy using the new triethylamine dimethyl zinc adduct in combination with diisopropyl telluride as zinc and tellurium precursors respectively. The influence of the growth temperature (T(g)), the VI/II molar ratio, and the overall growth pressure (P) are studied. The successful growth of ZnTe is demonstrated at temperatures as low as 300-degrees-C. For growth temperatures ranging between 300 and 450-degrees-C, the growth rate is limited by the kinetics at the growing interface, and we measure an activation energy of 28 kcal/mol. At T(g) = 375-degrees-C, we found a linear variation of the growth rate with the overall growth pressure on the one hand, and with both zinc and telluride molar flows on the other hand. Low temperature reflectance and photoluminescence measurements were performed to characterize all the samples and are used to determine the optimal growth conditions: T(g) = 350-degrees-C, VI/II = 2, with P = 40 Torr. The stress experienced by the epilayers is investigated using the reflectance measurements. The relative intensity of the arsenic related bound exciton emission at 2.367 eV decreases as T(g) decreases. On the other hand, the I(b)1 unknown acceptor related bound exciton emission at 2.356 eV decreases linearly with the growth rate.

In this communication we show that the cancelation of excitonic effects by photo-injected carriers can be easily produced in ZnSe-ZnTe superlattices. This combination is interesting : it has a type II band alignment in real space. Strong confinements of electrons and holes by large bands offsets lead to important values of Rydberg energies ; thus, important energy-shifts of some 20 meV are measured when exciton screening is produced in such superlattices.

Quantum-well ground and excited states are observed using wavelength-modulated reflectivity in InxGa1-xAs/AlyGa1-yAs single-quantum-well structures. To account for the dependence of their energies on indium and aluminum concentrations, we find that it is necessary to include the coupling between the light-hole GAMMA(8) valence band and the spin-orbit split-off GAMMA(7) valence band. The calculation is performed using a two-band envelope-function approximation, and good agreement with experiment is obtained.

We have studied the reflectance and photoluminescence spectra of a series of GaAs/AlAs superlattices grown by molecular beam epitaxy on GaAs (001) substrates exactly oriented or slightly misoriented. It is shown that the substrate misorientation has spectacular effects on the excitonic transition properties, strongly depending on the misorientation direction. The anisotropic dependencies of the exciton broadening and the emission line Stokes-shift are analyzed on the basis of a qualitative understanding of the interface structures.