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.

We have performed detailed optical measurements of ultrathin InAs/InP quantum wells grown by metal organic vapor phase epitaxy. Photoluminescence excitation spectra reveal the excitonic resonances associated with two- and three-monolayer thick InAs layers while polarization-dependent measurements clearly show the heavy- or light-hole nature of the resonances. These resonances, together with their emission bands, can be detected on the same sample, indicating the presence of well defined regions of different InAs layer thickness. We find that the energy position of the excitonic resonances cannot be reproduced by effective mass calculations based on the envelope function approximation.

The various mechanisms responsible for the strain relaxation of strain-compensated GaInP/InAsP multilayers grown on InP(001) using low-pressure organometallic vapor-phase epitaxy (LP-OMVPE) were investigated using a combination of transmission electron microscopy (TEM), high-resolution x-ray diffraction (HRXRD), and reciprocal lattice mapping. We examined separately the effect of the misfit strain f as well as the total strain energy εT on the strain relaxation mechanisms. We also investigated the effect of the growth temperature Ts on roughening. For the structures composed of a small number of superlattice periods, N=10, TEM and HRXRD indicate that strain relaxation occurs essentially through non-homogeneities at the interfaces for increasing misfit strain f values (at least up to |f|=1%, the largest strain used in these experiments). In comparison, when the magnitude of the misfit strain is kept constant, increasing the number of periods eventually leads to a massive generation of dislocations in the multilayer. For |f|=0.75%, coherency breakdown was observed around the 14th–15th period in a 50-period sample. However, the strain-compensated multilayer structures can be in a metastable state since all layers are perfectly flat and no dislocations are visible in a 20-period sample with the same misfit strains in the layers. Finally, we observed that the growth temperature Ts had a drastic effect on the morphology of the layers: increasing Ts from 620 to 680 °C while keeping all other growth parameters constant introduced large periodic lateral thickness modulations as well as dislocation clusters in the structures. Diffraction contrast analysis in plan-view TEM indicates significant anisotropy with the features elongated in the [11̄0] direction. These results could be used as guidelines for the design of highly perfect and reliable device structures grown by LP-OMVPE.

We have investigated the effect of the misorientation (001) InP substrates on the optical properties of submonolayers of InAs in InP grown by metalorganic chemical vapor deposition. InAs submonolayers were systematically studied using low temperature photoluminescence (PL), photoluminescence excitation spectroscopy and temperature-dependent, excitation density PL. For submonolayer samples with oriented substrates, the observed PL linewidths and energies are satisfactorily explained within a two-dimensional (2D) quantum well picture. The formation of InAs isolated quantum dots which is found in the submonolayer samples with misoriented substrates towards (110) orientations, however, results in 0D exciton localization.

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