Low-and room-temperature optical absorption spectra are presented for a series of InAs x P 1Ϫx /InP strainedlayer multiple quantum well structures ͑0.11 рxр0.35͒ grown by low-pressure metal-organic vapor phase epitaxy using trimethylindium, tertiarybutylarsine, and phosphine as precursors. The well widths and compositions in these structures are exactly determined from the use of both high-resolution x-ray diffraction and transmission electron microscopy on the same samples. The absorption spectra are then analyzed by selfconsistently fitting, for the five samples, the excitonic peak energy positions with transition energies determined from a solution to the Schrödinger equation in the envelope function formalism using the well-known Bastard/Marzin model ͓J. Y. Marzin et al., in Semiconductors and Semimetals, edited by Thomas P. Pearsall, ͑Academic, New York, 1990͒, Vol. 32, p. 56͔. From these self-consistent fits, both the bowing parameter of bulk unstrained InAs x P 1Ϫx and the band offsets of the heterostructures are deduced self-consistently. The conduction-band offsets thus determined represent 75%Ϯ3% of the total strained band-gap differences at both low ͑liquid He͒ and room temperatures. These values of the band offsets are consistent with the predictions of the quantum dipole model ͓J. Tersoff, Phys. Rev. B 30, 4874 ͑1984͔͒. The values determined for the bowing parameters are found to differ slightly between 0.10Ϯ0.01 eV at low temperature and 0.12Ϯ0.01 eV at room temperature.

A detailed investigation of the structural and optoelectronic properties of thick GaInP epilayers on sulfur-doped InP substrates is reported. Significant variations of the optical absorption and photoluminescence transition energies from light- and heavy-hole states are observed as a function of the epilayer composition as well as of the degree of relaxation of the misfit strain. High-resolution x-ray measurements were used to determine the Ga concentrations and the strains and indicate significant anisotropic relaxation in several films. Even small relaxations result in a significant increase in the optical linewidths and a rapid drop in the transition intensities. A model with no free parameters based on the strain Hamiltonian of Pikus and Bir provides excellent agreement with the transition energies and serves to identify unambiguously the transitions observed in the optical spectra. Within this model, isotropic in-plane relaxation produces a shift of both light- and heavy-hole energies whereas anisotropic in-plane relaxation contributes only negligibly.

Valence-band splitting and band-gap reduction in ordered GaInAs/InPStrain relaxation and exciton localization effects on the Stokes shift in InAs x P 1−x /InP multiple quantum wells

Heteroepitaxial InP layers were grown on Si(111) by metalorganic vapor phase epitaxy using thermal cycle growth. The best crystallographic and optical quality was obtained when thermal cycle growth was begun after only a thin InP layer had been deposited. High resolution x-ray diffraction rocking curves of 4.8 μm thick InP layers yield full widths at half-maximum as low as 76 arc s and show that epilayers have a positive tilt with respect to the substrate. Cross-section transmission electron microscopy observations and Rutherford backscattering measurements show that thermal cycling induces a net reduction of defect density in the interfacial region. Photoluminescence (PL) measurements performed on the best quality thermal cycle grown sample show a thermal strain induced energy splitting of 3.8 meV between the free exciton emissions associated with heavy and light holes. Two other peaks in the PL spectra correspond to acceptor-bound (A0,X)mj=±3/2 and (A0,X)mj=±1/2 excitonic transitions, as confirmed by photoluminescence excitation measurements. Their full width at half-maxima are 1.4 and 0.9 meV, respectively, for the optimized samples. They may be associated with Si acting as an acceptor.