InSb Quantum Dots Research Articles

Midinfrared Injection-Pumped Laser Based on a III–V∕II–VI Hybrid Heterostructure with Submonolayer InSb Insets

Lasing at 3.075 μm (T = 60 K) in a regime of pulsed injection pumping has been obtained in an AlGaAsSb/InAs/CdMgSe double hybrid heterostructure with the active region comprising an InAs layer with submonolayer InSb insets. The electroluminescence (EL) spectrum of the heterostructure has been studied for various values of the pumping current up to the stimulated emission threshold. An increase in the pumping current leads to a short-wavelength shift and a change in the EL band structure, which is explained by the occupation of higher states by the charge carriers in InSb quantum dots and/or in the adjacent InAsSb layer.

Spin-orbit and electronic interactions in narrow-gap quantum dots

We present a detailed analysis of spin-orbit couplings in zinc-blende narrow-gap parabolic quantum dots built in the plane of a two-dimensional electron gas. Such couplings are related to both bulk (Dresselhaus) and surface (Rashba) inversion asymmetry terms in the Hamiltonian of the system. We start by focusing on how the pure Fock-Darwin spectrum of an InSb quantum dot is modified by the addition of separate terms of spin-orbit coupling; we then deal with the presence of all spin-orbit terms in the numerical diagonalization of the single-particle model. We also consider a two-electron quantum dot---by antisymmetrizing the one-electron basis---and study the competition between electron-electron and spin-orbit interactions. All these effects are analyzed in the presence of a magnetic field perpendicular to the quantum dot. Selection rules for spin-orbit-induced level anticrossings, as well as critical fields and energy minigaps related to them, zero-field energy splittings, and the role of the $g$-factor on the spectrum are also addressed.

Mid-infrared electroluminescence from coupled quantum dots and wells

Room temperature electroluminescence between 1.7–2.6μm has been observed from coupled quantum dots and quantum wells in the InAs∕InSb∕GaSb materials system. The samples studied consist of a single narrow InAs quantum well grown below a layer of InSb quantum dots in a GaSb matrix. The thickness of the GaSb spacer layer lowers the energy from that of a quantum well alone but with a dependence that cannot be described solely through electronic coupling of the wave functions. A sharp transition occurs after a single monolayer coverage of GaSb either due to structural changes in the quantum dots or from shrinkage of the quantum well. For slightly thicker layers the emission energy can be explained by segregation during growth or strain-mediated correlation of the localized states in the system.

Self-assembled InAsSb quantum dots on (001) InP substrates

Self-assembled InAsSb quantum dots (QD) on (001) InP substrates have been grown using metalorganic vapor phase epitaxy. The dot density and size are found to be strongly dependent on the presence of arsine. Direct deposition of InSb on InP and GaSb substrates formed large islands of InSb with low density of less than 5×109/cm2, however, InAsSb QDs of density as high as 4×1010/cm2 could be self-assembled by alternating group III and group V precursors, and high density almost pure InSb QDs were achieved on In0.53Ga0.47As/InP. The formation of high density InAsSb QDs is a result of a local nonequilibrium process and a reduction in mobility of In adatoms on the growth surface due to the presence of arsenic atoms, and in the case of high density almost pure InSb QDs on InGaAs/InP, the InAs interface layer is believed to be responsible. Photoluminescence shows that InSb QDs emit light at room temperature in the range of 1.7–2.2 μm.

Far infrared modulated photoluminescence in InSb quantum dots

The first FIRM-PL measurements in InSb/GaSb quantum dots have been performed. At low power densities the FIR absorption causes a transfer of carriers between dots and effectively cools the system, preferentially populating large, low energy dots and increasing the photoluminescence (PL) intensity. At higher powers the carrier temperature increases and the PL intensity falls. The spectral dependence of the FIRM-PL signal measures the energy spectrum of the quantum dots, showing a peak at 14.5 meV corresponding to transitions between the first two energy levels of the quantum dot distribution.

Mid-infrared luminescence from coupled quantum dots and wells

Coupled nanostructures have been developed in the InAs/InSb/GaSb materials system in order to extend the emission wavelength further into the infrared, beyond 2 μm . The samples studied consist of a single narrow InAs quantum well grown below a layer of InSb quantum dots in a GaSb matrix, in which the coupling has been altered by changing the thickness of a GaSb spacer layer. The overall transition energy of the combined dot–well system is generally reduced with respect to the dots and well only but the dependence on spacer thickness is more complex than that expected from a simple envelope function model.

Properties of narrow gap quantum dots and wells in the InAs/InSb/GaSb systems

The properties of InSb quantum dots grown by metal organic vapour phase epitaxy are summarised as deduced from photoluminescence, magneto-photoluminescence, and far-infrared modulated photoluminescence experiments. A technique is described for shifting the emission of these dots to lower energy by coupling them with a narrow InAs quantum well, leading to the demonstration of electroluminescence at ∼2.3 μm .

Magneto‐photoluminescence studies of a novel quantum dot–quantum well coupled system

AbstractWe report a study of novel structures in which an InSb quantum dot (QD) layer in GaSb is coupled to a nearby narrow InAs quantum well (QW). Magnetic fields have been used to probe the photoluminescence (PL) of the dots and the wells separately and in the coupled structures. We have found that the introduction of the dot–well coupling leads to a dramatic suppression of the diamagnetic shift of the exciton when the magnetic field is oriented parallel to the well plane. The observed shift is 1–2 meV with an applied field of 17 T. In contrast, when the field is perpendicular to the layer plane, there is little difference in the response of the coupled structures compared to that of the quantum wells on their own, suggesting that the behaviour is dominated by the motion of the electrons in the wells.

Evolution of In‐based compound semiconductor quantum dots on Si (001)

The morphological evolution of InAs and InSb quantum dots grown on Si (001) by molecular beam epitaxy was studied by reflection high-energy electron diffraction and scanning probe microscopy. For the InSb/Si system, the maximum density of 1�×�1010�cm–2 was achieved at a growth temperature of 200�°C with the average base length and dot height of 80 nm and 1 nm, respectively. A broad luminescence band extending over 1.1–1.4�μm was observed at low temperature from the In-based quantum dots embedded in Si. The decay lifetimes of luminescence were of the order of submicroseconds, which indicates an indirect transition both in real- and in k-space. Excessive thermal budget after the growth only resulted in the development of luminescence features characteristic of In-doped Si.

Photoluminescence of self-assembled InSb quantum dots grown on GaSb as a function of excitation power, temperature, and magnetic field

We report measurements of photoluminescence (PL) from self-assembled InSb quantum dots (QD's) grown by metal-organic vapor-phase epitaxy in a matrix of GaSb as a function of excitation power, temperature, and magnetic field. PL is observed in the region 1.7--1.8 \ensuremath{\mu}m from InSb quantum dots. For low excitation power the PL is dominated by the lowest quantum dot transition energy. When the excitation power is increased the quantum dot transition increases in energy by \ensuremath{\sim}11 meV, and further transitions are observed from the wetting layer, bulk acceptor, and free excitons. Magneto-PL is used to calculate the in-plane dot confinement energies by fitting the data to the ground state of a Fock-Darwin set of energy levels. The in-plane confinement energy deduced increases from \ensuremath{\sim}6 to \ensuremath{\sim}18 meV as the excitation power is increased. This is similar to the increase in the quantum dot transition energy, and suggests that this is due to a progressive population of a distribution of strongly communicating dots with decreasing lateral sizes. Further support for this picture comes from the temperature dependence of the quantum dot transition energy, which is also found to increase by a relatively similar amount as the temperature is raised from 11 to 50 K, following a correction for the temperature dependence of the bulk energy band gaps.

Spin-Orbit Energy State Splitting in Semiconductor Cylindrical and Spherical Quantum Dots

We present a theoretical study of the spin–orbit interaction impact on electron energy states in small cylindrical and spherical quantum dots. The investigation is based on the effective one-electronic band Hamiltonian and the spin dependent boundary conditions. It has been demonstrated that the spin–orbit interaction can significantly modify the energy spectrum of InAs and InSb quantum dots. The splitting can provide a situation where only the lowest spin split energy states are bound in the dot. A reasonable agreement was found with data from more sophisticated theoretical models for the spherical quantum dots which is available in the literature.

Spin-orbit splitting in semiconductor quantum dots with a parabolic confinement potential

We present a theoretical study of the effect of spin-orbit interaction on the electron energy spectrum of cylindrical semiconductor quantum dots. The study is based on a simple effective one-band approximation. The dependence of energy levels on parameters of the dots and the applied external magnetic field is studied. Contributions of the bulk inversion asymmetry (the Dresselhaus term) and the system inversion asymmetry (the Rashba term) to the spin splitting of the electron energy states are discussed. The spin splitting of electron states with nonzero angular momentum is demonstrated theoretically for InSb and InAs small quantum dots at zero magnetic field. We find a ``crossing'' of the electron energy states with the same angular momentum and different spin polarizations in a nonzero magnetic field.

Liquid phase epitaxial growth and morphology of InSb quantum dots

In this paper we report on the morphology of InSb quantum dots (QDs)grown by liquid phase epitaxy on InAs and GaAs substrates. Small and large QDsare observed on both these two substrates, the resulting structures beinggenerally similar to those produced by MBE and MOVPE. The density of the smallQDs is approximately 1010 cm-2, with dimensions of 5-15 nm inheight and 0.1-0.3 aspect ratio. The density, size and shape of the small QDswere found to change with growth temperature, supercooling and melt-substratecontact time. The large QDs appear to be at a much lower density, beingapproximately 2×107 and 1×109 cm-2 for growth on GaAsand InAs substrates, respectively. Furthermore, it was found that thedifference in QD diameters becomes smaller as the lattice mismatch decreases.

MOVPE grown self-assembled and self-ordered InSb quantum dots in a GaSb matrix assessed by AFM, CTEM, HRTEM and PL

Self-assembled InSb quantum dots (QDs) were grown by metal-organic vapour phase epitaxy (MOVPE) in a GaSb matrix. Atomic force microscopy (AFM), conventional diffraction contrast transmission electron microscopy (CTEM), high resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) were used for the assessment of the QDs. Reductions in the III/ V ratios and growth rates resulted in a change of the morphology of the InSb islands from hillocks without facets, and a low level of order to dumbbell shaped islands with distinct facets and a higher level of order.

MOVPE grown self-assembled Sb-based quantum dots assessed by means of AFM and TEM

Self-assembled Sb-based quantum dots (QDs) were grown by metal-organic vapour phase epitaxy and assessed by means of atomic force microscopy, transmission electron microscopy and photoluminescence. Two series of InSb QDs in a GaSb matrix were grown at 490±10°C and luminesced in the mid-infrared at about 1.7 μm. Reductions in the III/V ratio and growth rate as used for the second series resulted in a change of the morphology of the InSb islands from hillocks without facets and a low level of order, to dumbbell shaped islands with distinct facets and a higher level of order. Self-assembled GaSb islands were grown on GaAs at 550°C and assessed for comparison by means of AFM.

Electronic structure in narrow-gap quantum dots

In this work we calculated the electronic structure of spherical quantum dots based on zincblend semiconductor compounds. The strong conduction-valence band coupling in this class of semi-conductors induces a strong mixing of the electronic states which requires a theoretical model to properly take into acount these effects. We have used a full 8 x 8 Kane Hamiltonian in order to include the strong admixture and study the set of symetries associated with these electronic states and their angular momentum in this central force problem. As an application, we have calculated the electronic structure in narrow-gap HgCdTe, InSb and CdTe quantum dots.

Self-assembled InSb quantum dots grown on GaSb: A photoluminescence, magnetoluminescence, and atomic force microscopy study

We report a study of self-assembled quantum dots (QDs) of InSb embedded in a GaSb matrix grown by metalorganic vapor phase deposition. Growth temperatures and deposition times have been optimized for maximal photoluminescence peak intensities. Photoluminescence (PL), magneto-PL, and atomic force microscopy (AFM) have been performed to estimate the size of the QDs. The quantum dots luminesce in the midinfrared at around 0.73 eV. The application of magnetic fields up to 15 T both parallel and perpendicular to the growth direction enhanced the wetting layer and bulk PL intensity and enabled an estimate to be made of the QD height and widths as 2–4 and 20–30 nm, respectively. These sizes were confirmed by AFM.

Morphology evolution of InSb island grown on InP substrates by atomic layer molecular beam epitaxy

The growth evolution of capped InSb quantum dots grown on InP(001) substrates is reported for a range between 0.6 and 15 monolayers of InSb deposited by atomic layer molecular beam epitaxy. TEM studies have been performed in order to follow the progression in dot size and morphology. After the transition from an initial two-dimensional to a three-dimensional growth mode at 1.1 ML there is a range in which InSb nanometre scale islands are homogeneously distributed. Raman spectra have also been recorded to assess the effects of the introduction of the capping layer covering the islands, comparing the results with those of uncapped samples. The activation of the InSb TO mode is discussed in terms of the facetting of the dots by (001) and {111} sides observed prior to the cap deposition.

Formation of InSb quantum dots in a GaSb matrix

InSb nanoislands in a GaSb matrix have been fabricated and their structural and luminescence properties have been studied. The deposition of ∼1.7 monolayers of InSb in a GaSb(100) matrix has been found by transmission electron microscopy to result in a 2D-3D growth mode transition and formation of small InSb quantum dots (QDs) with lateral sizes of ∼10 nm. Bright luminescence due to these QDs is observed. Stacking of the QDs results in a formation of vertical-coupled QD planes and leads to a long wavelength shift of photoluminescence line associated with the QDs. Increase in the InSb layer thickness above ∼2 monolayers results in formation of 3D dislocated InSb islands with a lateral size above 60 nm and the dramatic drop of photoluminescence intensity.

Characteristics of Self-Assembled InSb Dots Grown on (100) AlGaSb by Molecular Beam Epitaxy

A self-assembling method to produce dense InSb quantum dots on Al0.5Ga0.5Sb is reported. Samples were grown on (100)-oriented GaAs substrates by molecular beam epitaxy and characterized by reflection high-energy electron diffraction, atomic force microscopy, Raman spectroscopy and photoluminescence. Low-temperature deposition of InSb combined with an in situ post annealing resulted in small-sized three-dimensional islands as high as 1010 cm-2 acting as quantum dots, while deposition at 400°C yielded much larger sized islands at low density. It is also shown that the density and size of the islands are controllable by changing the annealing conditions.