M.M.G. de Carvalho

Role of group V exchange on the shape and size of InAs/InP self-assembled nanostructures

We have studied the influence of Group V overpressure on the final shape and size of InAs nanostructures grown on (001) InP substrates. The mechanisms leading to postgrowth modifications in the InAs nanostructures are discussed. The simultaneous action of Group V overpressure and stress field—produced by the InAs nanostructures—can induce strong material transport. The direction of this material net current depends on the type of Group V element used for the overpressure flux. In situ reflection high-energy electron diffraction, atomic force microscopy, and transmission electron microscopy measurements were used to characterize the transitions in morphology. Our results show that morphological studies considering the grown surface that do not take into account postgrowth processes can be misleading to understand the growth mechanisms governing the self-assembling process.

Faceting evolution during self-assembling of InAs/InP quantum wires

The self-assembling of InAs quantum wires on (001) InP substrates during chemical beam epitaxy has been studied. The samples were characterized by reflection high-energy electron diffraction (RHEED), atomic force microscopy, and high-resolution transmission electron microscopy (HRTEM). By monitoring the RHEED chevron structures along the [110] direction, we studied the facets formation during the initial states of InAs growth. The facets angles measured by HRTEM are in perfect agreement with the angles between chevron streaks. A time dependence of the chevron streaks angles is reported and correlated to the wire formation. These results can be interpreted using nonequilibrium models existing in literature.

Hybrid multiple diffraction in Renninger scan for heteroepitaxial layers

In this paper, we report the successful observation of the hybrid multiple diffraction (hybrid MD) in Renninger scans (RS) [M. Renninger, Z. Kristallogr. 106, 141 (1937)]. These diffractions occur when the beam first diffracted by an inclined layer (or substrate) plane with respect to the sample surface crosses the interface layer/substrate to be rescattered by another substrate (or layer) plane towards the detector. The construction of an incidence diagram allows to establish the occurrence of the hybrid MD for heteroepitaxial layers. The layer imperfection (mosaic spread) is used to explain these extra features in RS together along the normal MD features. The case of a GaAs layer grown on a Si substrate is investigated.

Spatial ordering in InP/InGaP nanostructures

We report the observation of a spatially-ordered bidimensional array of self-assembled InP quantum dots grown on slightly In-rich InGaP layers. The alignment of InP dots is observed along [100] and [010] directions. This effect is enhanced when 2° off vicinal substrates are used; it is also strongly dependent on growth temperature. Our results suggest that the density and size of CuPt-type atomically ordered regions as well as compositional modulation of InGaP layers play an important role on the spatial alignment of InP/InGaP quantum dots.

On the onset of InAs islanding on InP : influence of surface steps

Abstract We investigate the transition from two- to three-dimensional growth of thin InAs films on InP by chemical beam epitaxy. This transition is shown to strongly depend on growth temperature and on the misorientation-or the presence of surface steps — on the InP surface where the InAs film is deposited. Low temperature photoluminescence measurements on InP-InAs-InP quantum well structures and atomic force microscopy analysis of InAs-InP structures indicate different islanding behaviors for substrates with different misorientations, the onset of islanding process occurring earlier for misoriented than for nominal substrates. The shape and distribution of the islands indicate the existence of a step edge barrier altering the diffusion dynamics on the surface. Low growth temperature is shown to delay islanding for a fixed deposition time and also limit island formation to certain regions of the sample where smooth corrugations (slope ∼1°) are observed.

Electrical isolation of InGaP by proton and helium ion irradiation

Formation of electrical isolation in n- and p-type In0.49Ga0.51P epitaxial layers grown on semi-insulating GaAs substrates was investigated using proton or helium ion irradiation. Sheet resistance increases with the irradiation dose, reaching a saturation level of ≈109 Ω/□. The results show that the threshold dose necessary for complete isolation linearly depends on the original carrier concentration either in p- or n-type doped InGaP layers. Thermal stability of the isolation during postirradiation annealing was found to increase with accumulation of the ion dose. The maximum temperature at which the isolation persists is ≅500 °C.

A simple technique for Czochralski growth of GaSb single crystals from scum-free melt

Abstract A simple technique for synthesis and growth of GaSb crystals from a scum-free melt has been developed. The key element in this technique is the chemical and thermal treatment of gallium in vacuum before growth. This technique does not require the use of a pure hydrogen ambient nor the two-step process nor the double-crucible technique. Undoped and Te-doped 25 mm diameter GaSb single crystals of 〈100〉 orientation have been successfully grown by this technique with typical carrier concentrations of 1.0 × 1017 cm−3 and mobility of 717 cm2/V · s for undoped samples.

EVIDENCE OF BE3P2 FORMATION DURING GROWTH OF BE-DOPED PHOSPHORUS-BASED SEMICONDUCTOR COMPOUNDS

In this work, we present evidence that Be3P2 microcrystals are formed in Be-doped phosphorus-based semiconductor compounds grown by chemical beam epitaxy. Our results suggest that microcrystal formation occurs when high Be concentrations (>1018 cm−3) and temperatures higher than 500 °C are used for crystal growth. The main consequence of Be3P2 formation is a high phosphorus consumption close to these microcrystals that causes a large density of P vacancies in the semiconductor layer. This results in reduced electrical mobility, lattice parameter reduction, and poor crystalinity of the film in general.

Anisotropic unstable and stable growth of homoepitaxial (100) InP films

An extended study on the dynamics of growth of homoepitaxial InP films by chemical beam epitaxy is presented. Different morphologies (from layered to mounded) were achieved by changing growth temperature. In particular, ripples were observed at an intermediary temperature value. Their shape and evolution depend on both the direction and miscut angle of substrates used. Time and scale behavior of roughness and height-difference correlation functions calculated from atomic force microscopy data show that the average mound size increases during growth while the ripple wavelength remains approximately constant. Once ripples are present on the surface, growth becomes more stable due to surface faceting. Our experimental and simulation results indicate that competition between diffusion with anisotropic spatial bias and faceting play an important role in the growth process, giving rise to several different law regimes. When the film morphology is mounded, however, no stable temporal law regime is observed although a roughness exponent can still be measured, as expected for unstable growth with spatial diffusion bias.

Surface morphologies of Be-doped homoepitaxial InP films

We present here a study on the growth of Be-doped InP films by metalorganic molecular beam epitaxy, showing changes in morphology related to the presence of the dopant on the growing surface. The actual Be concentration in the films reaches (1-2) x 10 19 cm -3 while the hole concentration saturates at a lower value (∼2 x 10 18 cm -3 in our case). A negative lattice mismatch between film and substrate and non-uniform cathodoluminescence intensity are observed for samples grown at high growth temperatures and Be flux. The resulting changes in morphology suggest that the excess Be forms microclusters in the films grown at higher temperatures - due to the higher surface mobility, leading to the growth of oval defects. The surfaces of samples with no cap layer present a granulation which may be related to a reaction between Be and P at the growth temperature.