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An alternative way to characterise composition modulation in InxGa1−xP ALMBE layers grown on GaAs (001) substrate at a temperature of 420 °C by selective etching and photo etching is presented for the first time. AFM and TEM examinations revealed characteristic quasi-periodic surface structures consisting of ridges oriented along [110]. We propose that morphology features observed in the experiments are related to composition modulation effects.

In this work high structural and optical quality InxGa1−xP/GaAs quantum wells in a wide range of thicknesses have been successfully grown on GaAs substrates by low temperature atomic layer molecular beam epitaxy. We demonstrate that compositional fluctuations in the barrier alloy are responsible for the inhomogeneous broadening and spatial localization effects observed in the excitonic recombination, the influence of quantum well width fluctuations being negligible in comparison. An important change of the optical transition energies in these quantum wells is observed when tuning a 10% In–Ga ratio in the alloy around the lattice match composition (x=0.48). This change is related to the barrier band gap variation and the intrinsic characteristics of the InGaP/GaAs heterostructure: different exciton binding energy from tensile to compressive strain in the barrier, and a possible dependence of the conduction band offset on the In composition.

The effect of graded interfaces in step-graded buffer structures on crystal relaxation efficiency is investigated by transmission electron microscopy and double crystal X-ray diffraction. A higher recombination rate leading to higher edge dislocation densities and a strong diminution of the tilt, is evidenced when graded interfaces are used. The latter feature is a consequence of the poor stability of dislocation multiplication sources in graded interfaces. The lower strain energy release of dislocation segments and a diminution of the pinning points in graded interfaces reduce the lifetime of dislocations sources, producing a better distribution of Burgers vector in the misfit dislocations array.

We present a study of the relaxation behavior of compressive InxGa1−xP layers grown by atomic layer molecular‐beam epitaxy at Ts=420 °C with x=56%±3% and x=67%±3%. Similar (thickness and composition) InxGa1−xP layers were grown under different growth conditions in order to assess the influence of the stoichiometry of the growth front on the structural properties and the relaxation process of this material system. All InxGa1−xP layers were characterized by double‐crystal x‐ray diffraction, transmission electron microscopy, and Nomarski interference. Our results show that surface stoichiometry during growth does not affect the relaxation behavior of InxGa1−xP layers but strongly determines their structural characteristics related to composition modulation features which appear in all our InxGa1−xP layers. We have established an empirical relation between residual strain and thickness. This relation makes predictable the residual strain of more complicated structures which can be introduced as buffer layers in lattice‐mismatched heteroepitaxial systems.

GaAs pin and nip diodes have been grown by Atomic Layer Molecular Beam Epitaxy at 350°C on p-type and n-type (001) Si substrates respectively. These devices present different electrical characteristics. TEM characterization of these structures shows an asymmetric planar defect distribution whose orientation depends on the type of doping introduced in the GaAs layer immediately grown on the Si substrate. These results can be explained taking into account that the dissociation of dislocations depends both on the polarity of the dislocation and the doping type of the epilayer.

In this work we report the defect structure of GaAs layers grown on Si (001) substrates by atomic layer molecular beam epitaxy at 350 °C and conventional molecular beam epitaxy at 580 °C, investigated by transmission electron microscopy. It is found that the GaAs layers grown at 580 °C show high threading dislocation densities, whilst the majority defect types in the GaAs layers grown at 350 °C are stacking faults and microtwins. These results can be explained by taking into account that the mobility of partial dislocations depends on both the stress in the epitaxial layer and the growth temperature. According to this dependence, a transition from dissociated threading dislocations at a low temperature (350 °C) to perfect threading dislocations at a high temperature (580 °C) can be expected.

X-ray interference effect and transmission electron microscopy are used to study the relaxation process in a series of laser structures as a function of InAs content in the quantum well. It is shown that the X-ray interference effect is a powerful, fast and non-destructive method to assess the strain status in samples of this kind. A set of strained layer laser structures containing N monolayers of InAs (Nx(InAs)1(GaAs)3 with (N = 1, 3, 5, 7) in an 8 nm quantum well active region and a set of strained layer quantum wells consisting of P monolayers of InAs (Px(InAs)1(GaAs)Q with (P = 2, 4 and (Q = 2, 4) were grown [Dotor et al., J. Crystal Growth 127 (1993) 46] by atomic layer molecular beam epitaxy. X-ray interference effect and cross-section transmission electron microscopy analysis of the samples show that in the series of lasers with N monolayers of InAs the whole laser structure is coherent with the substrate (and consequently dislocation free) for 1 and 3 monolayers of InAs, while a sample with 5 monolayers of InAs is in a certain stage of relaxation (dislocation density nd {all equal to}107 cm-2) and a sample with 7 monolayers of InAs is almost completely relaxed (nd{all equal to}108 cm-2). In strained layer quantum well samples, the influence of the InAs/GaAs thickness ratio (P/Q) on the critical thickness has also been studied. These results are compared with those predicted by theoretical critical thickness models. Optical characterization as well as threshold current measurements of the lasers are correlated with X-ray diffraction and transmission electron microscopy relaxation status results. © 1993.

A high-resolution electron microscopy (HREM) study on antiphase boundaries in GaAs grown on Si is presented. HREM images of two close antiphase boundaries appearing mainly on the {110} planes which abruptly disappear suggest some ideas on the mechanisms of annihilation of these defects.

A study by high resolution electron microscopy and conventional transmission electron microscopy of the process of closure of antiphase boundaries (APB) in atomic layer molecular beam epitaxy (ALMBE) grown GaAs on silicon is reported. A parallelepipedical shape, closed at the top by another boundary with a semispheric shape, is proposed for the during growth suppressed APBs in GaAs epilayers. Antiphase boundaries are mostly located in {100} plans. Sixty degree dislocations are involved in the process of bending of APBs from {110} to {11n} planes; this bending is the initial step which must take place to get a single domain by interaction of two APBs. The proposed shape for closed APBs is in good agreement with the quasi two-dimensional growth observed for GaAs grown on silicon by ALMBE.