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InP was grown by chemical beam epitaxy in narrow windows of widths varying between 20 and 2 μm, oriented along the [011] or [01̄1] directions opened in a SiO2 mask on an (001) InP substrate. Several facets appear along the sidewalls and on the edge of the mesas owing to different growth rates on different crystallographic planes. These can be understood as consequences of the migration of group III species from one crystallographic plane to another. We have studied the formation of such facets and their effects on the growth of GaInAs/InP structures of various thicknesses. The samples were studied using a field emission scanning electron microscope (SEM) and low temperature photoluminescence (PL). SEM micrographs show that for lines oriented along the [011] direction the dominant InP sidewall facets are (111)B planes on which GaInAs does not grow as long as Ga and In species can migrate towards (001). For the orthogonal direction, however, the lateral growth rate of the InP sidewalls is large and the faceting of the mesas is more complicated. The PL spectra of GaInAs quantum wells grown on such mesas exhibit several peaks whose energy depends on the initial width of the mask. They can be interpreted in terms of crystallographic plane dependent migration and desorption rates of Ga and In species. The (111)B facets of [011] directed mesas were used to produce inverted V-shaped mesa wire structures.

We have measured the photoreflectance (PR) spectra at 300K and 77K of two strained layer <001> In Gal7As /GaAs (x =0.12) multiple quantum wells (MQW) with nominal well (LZ) and barrier (LB) widths of 50ii/1Ó0K and 30A /100A, respectively, as deduced from the growth conditions.Phototransmittance at 77K of the latter sample has been studied.In both samples we have observed a number of features in the PR spectra corresponding to miniband dispersion (coupling between wells) of both confined and unconfined (above the GaAs barrier) transitions.The coupling between wells leads to different transition energies at the mini -Brillouin zone center (r) and edge (rt) along the growth direction. This is the first observation of unconfined features and miniband dispersion in this system.Even though our samples have fairly wide barriers (L =100A) the coupling between wells is an important effect because of the relatively small confinementBenergies for x =0.12. Using the envelope function approach we have calculated the various transition energies taking into account both strain and quantum well effects, including miniband dispersion.Good agreement with experiment is found for a heavy -hole valence band discontinuity of 0.3 ±0.05 and LZ /LB = 52 ±3A /105 ±5A(x = 0.11 ±0.01) and 32 ±3A /95 ±5A(x= 0.12 ±0.01) for the two samples, respectively. The In composition and well /barrier widths are thus in good agreement with the growth conditions. Although the symmetric component of the fundamental light -hole to conduction band transition is a strong feature, the small observed amplitude of the antisymmetric component for both samples is evidence for the type II nature of the light -hole to conduction band transitions.

We have investigated the electronic properties of an Ino. l&Gao. &As-GaAs strained-layer superlattice using photoluminescence excitation and photocurrent spectroscopies. Flatband spectra show transitions at the center and edge of the Brillouin minizone, and photocurrent spectra at finite bias show the effects of Wannier-Stark quantization. The heavy-hole transitions evidence the importance of the excitonic interaction between spatially separated carriers. The light-hole transitions show a qualitatively different behavior resulting from their weak confinement in the GaAs layers. Our data agree with a numerical calculation of the electro-optical absorption spectra.In the last few years, there has been a considerable interest in strained-layer superlattices (SL) and quantum wells (QW), because of their fundamental interest and their potential for devices. ' Although a number of studies have been devoted to the In"Gal-"As-GaAs heterostructures, the electronic properties of this system are still a matter of controversy. 2 More recently, novel electrooptical properties of semiconductor SL's have been discovered.The investigation of these Wannier-Stark effects in the In"Gal "As-GaAs system is interesting in many respects. In particular, the strain-induced enhancement of the heavy-hole to light-hole splitting allows a complete separation of the corresponding absorption bands, which makes the observation of the zone-edge or "saddle-point exciton" 5 transitions much clearer than in unstrained SL's. Also, at least for large enough indium concentrations, the light holes must be confined in the GaAs layers, which gives an opportunity to observe the Wannier-Stark effects in the type-II SL configuration, for which a qualitatively new behavior is predicted. In addition, short-period SL's can be accurately characterized, and the study of the electro-optical properties of such In, Gal "As-GaAs SL's is likely to bring a definitive answer to the controversy on the band offsets in this system. In this Rapid Communication, we report investigations by photoluminescence excitation (PLE) and photocurrent (PC) spectroscopies of the electronic structure and electro-optical properties of a Inp|5Gaps5As-GaAs SL in which the well and barrier thicknesses are small enough to ensure a strong coupling of the wells in the flatband conditions and, at least for the heavy-hole transitions, a negligible intrawell Stark eAect.Our sample was grown by low-pressure metal-organic vapor-phase epitaxy on a Si-doped GaAs substrate. It consists of a 10-period SL grown on top of a 1.8 pm thick buff'er layer of undoped GaAs. All the layers were undoped with a residual carrier concentration n = 5x10'cm . An important advantage of periodic structures, with respect to characterization, is the easy evaluation of their structural parameters by x-ray diff'raction. Here, the analysis of the high-quality x-ray rocking curve indicated that no plastic relaxation occurred. ' An In concentration of 15% and thicknesses of 31 and 90 A. for the In"-Ga|-"As and GaAs layers, res...

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