Self‐assembled quantum dots of InSb grown on InP by atomic layer molecular beam epitaxy: Morphology and strain relaxation

Self-organized InSb dots grown by atomic layer molecular beam epitaxy on InP substrates have been characterized by atomic force and transmission electron microscopy. Measurement of high-energy electron diffraction during the growth indicates a Stransky–Krastanov growth mode beyond the onset of 1.4 InSb monolayer ~ML! deposition. The dots obtained after a total deposition of 5 and 7 ML of InSb present a truncated pyramidal morphology with rectangular base oriented along the ^110& directions, elongated towards the @110# direction with $111$113%/$114$111%A lateral facets in @11 ¯ 0# views, and ~001! flat top surfaces. The mismatch between the dot and the substrate has been accommodated by a network of 90° misfit dislocation at the interface. A corrugation of the InP substrate surrounding the dot has been also observedThis work has been funded by the Spanish CICYT Project MAT95-0966.Peer reviewe

Growth of quantum three-dimensional structure of InGaAs emitting at ~1 µm applicable for a broadband near-infrared light source

We obtained a high-intensity and broadband emission centered at ~1 µm from InGaAs quantum three-dimensional (3D) structures grown on a GaAs substrate using molecular beam epitaxy. An InGaAs thin layer grown on GaAs with a thickness close to the critical layer thickness is normally affected by strain as a result of the lattice mismatch and introduced misfit dislocations. However, under certain growth conditions for the In concentration and growth temperature, the growth mode of the InGaAs layer can be transformed from two-dimensional to 3D growth. We found the optimal conditions to obtain a broadband emission from 3D structures with a high intensity and controlled center wavelength at ~1 µm. This method offers an alternative approach for fabricating a broadband near-infrared light source for telecommunication and medical imaging systems such as for optical coherence tomography

In situ observation of surface optical anisotropy on InP, InAs, and InSb by chemical modulation spectroscopy

In situ observation of surface optical anisotropy due to In dimers in a set of three In-based semiconductor binary compounds—InP, InAs, and InSb—grown by molecular-beam epitaxy is reported. We used an optical reflection technique based on the chemical modulation of the surface, that permits the measurement with light linearly polarized in one selected polarization, usually [110] or [11¯0], typically parallel to the group-III and -V dimers. Spectra for (001) surfaces in the 1–3-eV range were obtained through this technique, and the results are compared to those previously obtained for a set of Ga-based binary compounds, GaP, GaAs and GaSb. For both sets, well-defined features for light polarized along [110] have been observed, that are attributed to transitions between the occupied group-III dimer and the unoccupied dangling-bond bands.This work has been partially supported by a CICYT MAT95-0966-C02-01 Research Action.Peer reviewe

Optical properties of InSb layers confined by InP

The photoluminescence properties of InSb submonolayers and dots are presented. When the amount of InSb deposit on InP is less than 1 ML the growth mode remains two dimensional, while for greater amounts three-dimensional quantum dots are formed. Within the two-dimensional growth mode range the energy of the InSb-related transition decreases as we increase the amount of InSb deposited within the limits of said range. No InSb absorption features have been detected. The observed photoluminescence is interpreted as a recombination of electrons in the InP layers with holes in the InSb layers. We estimate a valence-band offset of 1.525 eV, similar to the predictions of the solid-model theory (1.600 eV). In the samples with InSb dots an InSb related transition has been observed, which is attributed to the wetting layer.The authors would like to gratefully acknowledge support by the European Union ~HCM, network CT930349! and by CICYT under Project No. MAT95-0966Peer reviewe

In situ optical spectroscopy of Ga dimers on GaP, GaAs and GaSb by surface chemical modulation

The optical characterization of the surface anisotropy of three Ga-based semiconductor compounds using an in situ technique based on the chemical modulation of the surface is described. In this technique, the anisotropic optical reflectivity is modulated by a periodic variation of the surface stoichiometry using valved pulsed cells for group-V elements (As, P, Sb). The substrate is maintained at sufficiently high temperature in order to obtain rapid desorption of group-V molecules from the surface during flux interruptions. Linearly polarized light, reflected at near normal incidence by the sample, is collected separately along one of the two principal axes of the crystal, [110] and [11¯0]. The change in the surface coverage induces a change in the intensity of the reflected light, and the normalized variation ΔR/R is recorded as a function of wavelength. Spectra for (001) surfaces in the 1–3 eV range have been obtained with this method for a set of Ga-based binary III-V compounds GaP, GaAs, and GaSb, showing well-defined features for light polarized along the [110] direction, parallel to Ga dimers. These observed maxima are attributed to transitions between the occupied Ga dimer and the unoccupied dangling bond bands, at characteristic energies in each material.One of the authors (P. A.) acknowledges the support received from the Basque Government. This work was partially supported by a MAT95-0966 Research Action.Peer reviewe

Microstructure of Pyramidal Defects in InSb Layers Grown by Atomic Layer Molecular Beam Epitaxy on InP Substrates

PACS.61.72.-y Defects and impurities in crystals, microstructure PACS.68.55.-a Thin film structure and morphology PACS 61.16.-d Electron, ion and scanning probe microscopyWe report on the structural characterization of epitaxial InSb films grown on InP substrates by atomic layer molecular beam epitaxy at relatively low temperatures (330 ○C < T < 400 ○C). Moreover, we study the effect of the introduction of an intermediate InSb/InP buffer layer grown by molecular beam epitaxy. The studies were carried out by TEM and HRTEM, to investigate the densities and nature of the defects and the accommodation mechanism between the two types of layers which have a large lattice mismatch (10.4%). Results show a high defect density at the interface vicinity whatever the growth method employed, with or without buffer layers, but better quality layers are obtained as growth proceeds. The prevailing type of defects are threading dislocations and stacking faults for both types of samples, but the introduction of the intermediate layers leads to the formation of two types of complex three-dimensional defects, consisting in crystal misorientations, that induce an anomalous growth of the InSb layer leading to different growth rates and the formation of pyramidal or truncated pyramidal hillocks on the surface. In this case scanning electron microscopy and Raman analysis were also performed to study the influence of the defects on surface morphology and confirm their structure. Moreover, anisotropy of the stacking fault distribution is noticed in this sample: the density for [ $\bar{110}$] –(111)A slip planes is higher than for the [110]–(111)B slip planes. Strain due to large lattice mismatch is relieved in both types of samples by the generation of a pure edge-type misfit dislocation array.This work was funded by the Spanish CICYT program MAT95-0966.Peer reviewe

Submonolayer sensitivity of InSb on InP determined by friction-force microscopy

Using molecular-beam-epitaxy-grown InAs and InSb on InP(001) surfaces, we show that the friction-force microscope is sensitive to monolayer coverage. Those surfaces are characterized by three-dimensional islands separated by flat regions. For a constant load, the frictional forces measured on the InAs island and on the substrate are the same. This is due to the formation of a two-dimensional wetting layer (1.5 ML) of InAs covering the InP(001). The frictional force is controlled by the interaction of this layer and the tip. In contrast, the deposition of 2 ML of InSb on InP(001) produces a different behavior. The frictional force changes when the tip moves from the island to the flat region. Photoluminescence and atomic-force-microscopy experiments show the formation of an InSb submonolayer. The sensitivity of the friction-force microscope to monolayer coverage illustrates its usefulness for wetting-layer analysis. Based on these results we discuss the potential of the friction-force microscope to develop a spatially resolved friction spectroscopy.This work was supported by Dirección General de Investigación Científica Técnica of Spain (PB94-0016).Peer reviewe

Resonant Raman scattering study of InSb etched by reactive ion beam etching

A Raman study of InSb etched by reactive ion beam etching using a CH4 /H2 /N2 plasma generated by electron cyclotron resonance is presented. The evolution of the LO, 2LO phonon and phonon plasmon coupled modes has been studied using resonant Raman spectra in different configurations. Results indicate an increase of the carrier density by a factor of about 60 and a decrease of the built-in potential due to the plasma process. The combination of both evolutions results in a prevalence of the electric field induced scattering upon the defect induced scattering mechanism.Peer reviewe

Transition from self-organized InSb quantum-dots to quantum dashes

3 pages, 4 figures.We have grown self-organized InSb quantum dots on semi-insulating InP (001) substrates by molecular beam epitaxy. We studied the size dependency of the uncapped InSb quantum dots on the nominal thickness of the deposited InSb by atomic force microscopy. The dot sizes have a pronounced minimum at about 2.2 monolayers of InSb. After a nominal thickness of 3.2 monolayers we observe a drastic change of the dot shape, from quantum dots to quantum dashes. From there on the dots grow in a quasicylindric shape aligned in the (110) direction.The authors would like to acknowledge gratefully financial support from the European Union (HCM, Network CT930349).Peer reviewe

Raman scattering of InSb quantum dots grown on InP substrates

In this paper we present the Raman scattering of self-assembled InSb dots grown on (001) oriented InP substrates. The samples were grown by pulsed molecular beam epitaxy mode. Two types of samples have been investigated. In one type the InSb dots were capped with 200 monolayers of InP; in the other type no capping was deposited after the InSb dot formation. We observe two peaks in the Raman spectra of the uncapped dot, while only one peak is observed in the Raman spectra of the capped dots. In the case of the uncapped dots the peaks are attributed to LO-like and TO-like vibration of completely relaxed InSb dots, in agreement with high resolution transmission electron microscopy photographs. The Raman spectra of the capped dot suggest a different strain state in the dot due to the capping layer