J. Bettini

Mechanism of lateral ordering of InP dots grown on InGaP layers

The mechanisms leading to the spontaneous formation of a two-dimensional array of InP∕InGaP dots grown by chemical-beam epitaxy are discussed. Samples where the InGaP buffer layer was grown at different conditions were characterized by transmission electron microscopy. Our results indicate that a periodic strain field related to lateral two-dimensional compositional modulation in the InGaP buffer layer determines the dot nucleation positions during InP growth. Although the periodic strain field in the InGaP is large enough to align the InP dots, both their shape and optical properties are effectively unaltered. This result shows that compositional modulation can be used as a tool for in situ dot positioning.

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.

Compositional modulation and surface stability in InGaP films: Understanding and controlling surface properties

We investigate the formation of compositional modulation and atomic ordering in InGaP films. Such bulk properties—as well as surface morphologies—present a strong dependence on growth parameters, mainly the V/III ratio. Our results indicate the importance of surface diffusion and, particularly, surface reconstruction for these processes. Most importantly from the application point of view, we show that the compositional modulation is not necessarily coupled to the surface instabilities, so that smooth InGaP films with periodic compositional variation could be obtained. This opens a new route for the generation of templates for quantum dot positioning and three-dimensional arrays of nanostructures.

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.

High-resolution synchrotron radiation Renninger scan to examine hybrid reflections in InGaP/GaAs(001)

High-resolution synchrotron radiation Renninger scans (RS) have been used in the analysis of hybrid reflections in the InGaP/GaAs structure. Four-beam cases involving two Bragg (primary and secondary) and one Laue (secondary) reflections of the 002 Renninger scans for the GaAs substrate and the InGaP layer were analysed in detail. Different structures of asymmetry regarding the in-plane directions [110] and [1{\bar 1}0] were observed from the measurements of the same three families of four-beam cases, {1{\bar 1}}{\bar 1}/{1{\bar 1}}3, {20}0/{20}2 and {3{\bar 1}}{\bar 1}/{3{\bar 1}}3, at several φ positions. The comparison between the experimental and MULTX simulated scan clearly shows a marked asymmetry observed on the {20}0/{20}2 contributions. An asymmetric peak instead of the simulated dip appears due to the layer Laue secondary beam {20}0 crossing the layer/substrate interface to generate a hybrid peak. The break in the lattice coherence for this heterostructure is shown by the occurrence of an unexpected dip in the layer RS, which does not obey the mirror symmetry.

Residual carbon and carrier concentration in InGaP layers grown by chemical beam epitaxy

Abstract In this work we present a study on the carbon incorporation in InGaP layers grown by Chemical Beam Epitaxy as a function of growth temperature. Hall measurements show that the electron concentration increased from 2.3×1014 to 8.9×1016 cm−3 as the growth temperature increased from 500 °C to 560 °C. Lower growth temperature InGaP layers are more resistive. Using photoluminescence and a carbon-implanted sample, we identify an acceptor level at nearly 45 meV from the top of the valence band. Part of incorporated carbon acts as an acceptor and part as a donor. The electrical and photoluminescence measurements show that the ratio between acceptors and donors increase as the growth temperature decreases. Due to this compensation, samples grown at lower temperatures (500 °C) present a resistively 104 times higher than those grown at high temperature (560 °C).

Evidence of formation of Si-C bonds during growth of Si-doped III-V semiconductor compounds

In this work, we demonstrate that Si–C bonds are formed in III–V semiconductor compounds grown by chemical beam epitaxy. Our results suggest that the formation of Si–C bonds occurs in III–V epitaxial layers with acceptor Carbon residual concentration and high Si concentrations (>1017cm−3). The main consequence of Si–C bonds is the generation of defects along [111] direction. These defects produce carrier concentration saturation, reduction of electrical mobility, crystal quality degradation, and surface defects.

Spatial composition dependence in InGaP growth on pre-patterned GaAs substrates by chemical beam epitaxy

We have investigated the spatial composition variation in InGaP layers grown by chemical beam epitaxy (CBE) on pre-patterned substrates. At growth temperature of 540°C, no difference between In and Ga growth properties is observed. At 500°C, we observe the onset of new crystalline planes on the side walls of the pre-patterned structure. Finally, we show how these planes are related to a measured strong spatial composition variation.

Exploring Au Droplet Motion in Nanowire Growth: A Simple Route toward Asymmetric GaP Morphologies

Here we show a new nanowire growth procedure, exploring the thermally activated motion of Au droplets on III-V surfaces. We show that by setting a single growth parameter we can activate the crawling motion of Au droplets in vacuum and locally modify surface composition in order to enhance vapor-solid (VS) growth along oxide-free areas on the trail of the metal particle. Asymmetric VS growth rates are comparable in magnitude to the vapor-liquid-solid growth, producing unconventional wurtzite GaP morphologies, which shows negligible defect density as well as optical signal in the green spectral region. Finally, we demonstrate that this effect can also be explored in different substrate compositions and orientations with the final shape finely tuned by group III flow and nanoparticle size. This distinct morphology for wurtzite GaP nanomaterials can be interesting for the design of nanophotonics devices.

Heterostructure interface roughness characterization by chemical mapping: Application to InGaP/GaAs quantum wells

Interface quality is an important factor for the functionality of semiconductor modern devices. Routinely, these characteristics are probed qualitatively by photoluminescence. However, quantitative microscopic structural information to corroborate models is not commonly available. Among different techniques, atomic resolution transmission electron microscopy images represent the basic experimental method to analyze the quality of buried interfaces. In this work we describe the analysis of chemical changes determined from the quantitative comparison of intensity distribution across an interface in high resolution transmission electronic microscopy (HRTEM) images. We have shown that a careful analysis of HRTEM images contrast can provide extremely useful quantitative information on interface roughness. We have characterized four different samples of InGaP/GaAs quantum wells grown with different interfacial schemes. Limits in the quantification from different sources, such as sample preparation, sampling, an...