Electronic and optical properties of InSb quantum dots from pseudopotential calculation

The electronic and optical features of InSb spherical quantum dots have been investigated by a pseudopotential approach as a function of their radius taken in the range 1-10 nm. The direct- and indirect band gaps along with the electron and heavy hole effective masses are all found to be diminished as the quantum dot radius is increased. However, the refractive index, the static- and high frequency dielectric constant as well as the transverse effective charge are shown to be augmented by increasing the quantum dot radius. It is noted that the quantum confinement is of great impact on all the studied quantities for quantum dot radius below 6 nm. This could result in more opportunities to obtain desired optoelectronic properties that cannot be obtained in the bulk InSb materials.     

Enhanced optical nonlinearities of superlattices within the Kronig-Penney model incorporating inherent bulk nonlinearities

Third order nonlinear optical susceptibilities χ⁽³⁾ of GaAs/Ga_1?xAlAs superlattices have been predicted which are two orders of magnitude larger than those of bulk GaAs. This enhancement is due to the band nonparabolicity arising from the additional periodicity of the superlattice. These predictions, based on a tight-binding model of the superlattice dispersion, are here extended to the more realistic Kronig-Penney (KP) model. Corrections to tight-binding are non-negligible; however, enhancements of χ⁽³⁾ are still large but reduced approximately 30%–50% over previous estimates. The KP model is also here applied to superlattices employing InSb as the quantum well material. Because of the smaller effective mass of InSb, and taking account of its bulk nonparabolicity, the minibands move to higher energy, enhancing the interwell overlap and increasing χ⁽³⁾ by about one order of magnitude over that of bulk InSb. The role of the barrier material in this case is important and is discussed. The interplay between the bulk nonparabolicity and that arising from the superlattice is also addressed.     

Quantum oscillations in a hexagonal boron nitride-supported single crystalline InSb nanosheet

A gated Hall-bar device is made from an epitaxially grown, free-standing InSb nanosheet on a hexagonal boron nitride (hBN) dielectric/graphite gate structure and the electron transport properties in the InSb nanosheet are studied by gate-transfer characteristic and magnetotransport measurements at low temperatures. The measurements show that the carriers in the InSb nanosheet are of electrons and the carrier density in the nanosheet can be highly efficiently tuned by the graphite gate. The mobility of the electrons in the InSb nanosheet is extracted from low-field magneotransport measurements and a value of the mobility exceeding $\sim 1.8\times10^4$ cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$ is found. High-field magentotransport measurements show well-defined Shubnikov-de Haas (SdH) oscillations in the longitudinal resistance of the InSb nanosheet. Temperature-dependent measurements of the SdH oscillations are carried out and key transport parameters, including the electron effective mass $m^{\ast }\sim 0.028 m_{0}$ and the quantum lifetime $\tau \sim 0.046 $ ps, in the InSb nanosheet are extracted. It is for the first time that such experimental measurements have been reported for a free-standing InSb nanosheet and the results obtained indicate that InSb nanosheet/hBN/graphite gate structures can be used to develop advanced quantum devices for novel physics studies and for quantum technology applications.     

InSb/InAsSb nanostructures for Mid-IR optoelectronics

The technique of preparation of nanostructures with InSb quantum dots in an InAs(Sb) matrix, emitting in the mid-IR range upon optical and injection pumping, by molecular beam epitaxy is considered and the structural and optical properties of these nanostructures are investigated. The characteristics of the first injection lasers based on III–V/II–VI hybrid heterostructures with InSb/InAs(Sb) quantum dots in the active region are reported.     

Spectroscopy of spin-orbit quantum bits in indium antimonide nanowires

A double quantum dot in the few-electron regime is achieved using local gating in an InSb nanowire. The spectrum of two-electron eigenstates is investigated using electric dipole spin resonance. Singlet-triplet level repulsion caused by spin-orbit interaction is observed. The size and the anisotropy of singlet-triplet repulsion are used to determine the magnitude and the orientation of the spin-orbit effective field in an InSb nanowire double dot. The obtained results are confirmed using spin blockade leakage current anisotropy and transport spectroscopy of individual quantum dots.     

Quantum efficiency and overlap integrals in InSb

The paper deals with the problem of the enhanced quantum efficiency in semiconductors. An expression is derived for the spectral dependence of quantum efficiency in InSb in the low energy region. The probabilities both of the primary absorption process and of secondary relaxation processes, i.e. impact ionization (inter-band Auger transitions) and the thermalization of hot electrons, are calculated. The behaviour of overlap integrals in InSb is discussed in connection with these processes. The calculated spectral dependence of the quantum efficiency is compared with the experimental measurements.     

Probing electron-electron interaction in quantum Hall systems with scanning tunneling spectroscopy

Using low-temperature scanning tunneling spectroscopy applied to the Cs-induced two-dimensional electron system (2DES) on p-type InSb(110), we probe electron-electron interaction effects in the quantum Hall regime. The 2DES is decoupled from bulk states and exhibits spreading resistance within the insulating quantum Hall phases. In quantitative agreement with calculations we find an exchange enhancement of the spin splitting. Moreover, we observe that both the spatially averaged as well as the local density of states feature a characteristic Coulomb gap at the Fermi level. These results show that electron-electron interaction can be probed down to a resolution below all relevant length scales.     

Evidence for the existence of an unusual structure in the nanorods of InSb

Motivated by the recent prediction that InSb nanometer-diameter filaments can exhibit exotic physical properties, we have synthesized this material and have characterized the filaments. In this report, we describe the finding of an unusual phase of InSb. This new phase occurs when an InSb filament has a diameter of less than 100 nm. High-resolution X-ray-diffraction studies of InSb filaments, having radii ≅33.0 nm, indicate the InSb crystal lattice to be tetragonal, S.G. I4/mmm, with a unit-cell volume 12 times larger than that of the β-tin phase observed in bulk InSb above 2.0 GPa. The density of an InSb nanorod, as calculated from X-ray-diffraction data, is ∼22% more than that of the zinc-blende phase of InSb at ambient conditions, implying that the nanorod experiences a pressure of ∼2 GPa. In contrast, InSb nanorods with radii ≥50.0 nm are observed to show zinc-blende structure and densities nearly the same as that of the bulk. Received: 6 February 2002 / Accepted: 26 March 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-202/767-5301; E-mail: yousuf@seas.gwu.edu     

A double quantum dot defined by top gates in a single crystalline InSb nanosheet

We report on the transport study of a double quantum dot (DQD) device made from a freestanding, single crystalline InSb nanosheet. The freestanding nanosheet is grown by molecular beam epitaxy and the DQD is defined by the top gate technique. Through the transport measurements, we demonstrate how a single quantum dot (QD) and a DQD can be defined in an InSb nanosheet by tuning voltages applied to the top gates. We also measure the charge stability diagrams of the DQD and show that the charge states and the inter-dot coupling between the two individual QDs in the DQD can be efficiently regulated by the top gates. Numerical simulations for the potential profile and charge density distribution in the DQD have been performed and the results support the experimental findings and provide a better understanding of fabrication and transport characteristics of the DQD in the InSb nanosheet. The achieved DQD in the two-dimensional InSb nanosheet possesses pronounced benefits in lateral scaling and can thus serve as a new building block for the developments of quantum computation and quantum simulation technologies.     

InSb纳米晶体的生长和吸收光谱的研究

采用在惰性气体中蒸发的方法获得了沉积在ZnS基片上的InSb纳米晶体,其平均尺寸随惰性气体的压强增加而增大.从实验测量的室温吸收谱上看到,当纳米晶体的平均直径从27.9 nm减小到24.2nm再到21.4 nm时,其吸收边分别向高能方向移动了0.0151 eV和0.0145 eV.用有效质量近似模型计算了半导体纳米晶体的吸收边相对其体材料的移动,将理论计算与实验结果进行了比较.     

Anisotropic growth of indium antimonide nanostructures

InSb nanostructures have been synthesized by the use of gas aggregation process. Nanoparticles with different shapes are obtained by controlling the growth and deposition temperature of the InSb nanoclusters. Triangular nanocrystals are commonly observed when the clusters are extracted from the condensation chamber of the source and deposited on the room temperature substrate at high vacuum. When the deposition is performed inside the condensation chamber at high temperature near the melting point of bulk InSb, nanoparticles formed on the substrate surface show several kinds of 3-dimensional morphologies, such as triangular or rectangular prisms, as well as hexagonal tablets. Keeping the same conditions for the cluster source operation and deposition, after long time growth, nanorods with hexagonal and quadrangular cross sections are formed through vapor-liquid-solid (VLS) process. The origin of the difference on the morphologies and shapes of the nanostructures is attributed to the anisotropic growth of InSb, which is temperature dependent.     

Transient magnetoresponse of photoexcited electrons: Negative cyclotron absorption and evolution of Faraday angle

The transient magnetooptical response of electrons with partly inverted initial distribution produced by an ultrashort optical pulse near the optical phonon energy is studied theoretically. Transient cyclotron absorption and Faraday rotation of polarization plane are considered for bulk semiconductors (GaAs, InAs, and InSb) as well as for a GaAs-based quantum well. Damping of the response due to electron momentum relaxation associated with elastic scattering from acoustic phonons is taken into account in calculations, as well as the evolution of the electron distribution due to quasi-elastic energy relaxation at acoustic phonons and effective inelastic transitions accompanied by spontaneous emission of optical phonons. Nonstationary negative absorption in the cyclotron resonance conditions and peculiarities of Faraday rotation of the polarization plane associated with partial inversion of the initial distribution are considered. The possibility of transient enhancement of the probe field under cyclotron resonance conditions is indicated.     

Cyclotron resonance of inversion electrons on InSb in tilted magnetic fields

Cyclotron resonance (CR) of inversion electrons on InSb is studied in magnetic fields tilted away from the surface normal. Particularly, a pronounced splitting of the CR signals into two distinct resonances is observed. When the magnetic field is parallel to the inversion layer one of the two resonances vanishes and the other evolves into a bulk like CR at sufficiently low electron densities and in sufficiently high resonance magnetic fields. The different absorption modes are explained by a strong coupling of the electric and magnetic quantization on InSb in tilted magnetic fields.     

Electronic structure of ideal and relaxed InSb(110) surfaces

We report electronic structure calculations for the ideal and relaxed InSb (110) surfaces which were carried out using the tight binding scattering theoretic method. The bulk material is described by a realistic ETBM Hamiltonian and spin-orbit coupling has been taken into account explicitly. Our results show, that the spin-orbit interaction has only small influence on the surface electronic structure of InSb(110). Our results are discussed in terms of surface band structures, wavevector-resolved layer densities of states and angular-resolved weighted layer densities of states.     

熔体旋甩工艺对n型InSb化合物的微结构及热电性能的影响

采用新颖的熔体旋甩结合放电等离子烧结技术制备了单相InSb化合物,研究了熔体旋甩工艺对其微结构以及热电性能的影响. 结果表明,熔体旋甩得到的薄带自由面主要由300 nm—2 μm的小柱状晶组成,薄带接触面为非晶或精细纳米晶,薄带经烧结后得到了具有大量层状精细纳米结构的致密块体,尺寸约为40 nm. 与熔融+放电等离子体烧结制备样品相比,在测试温度范围内（300—700 K）,试样的电导率略有下降,但Seebeck系数显著增加,热导率和晶格热导率显著降低,室温下晶格热导率降低幅度约为106%,700 K下晶格热导率的降低幅度达1664%,熔融+熔体旋甩+放电等离子体烧结制备的InSb化合物试样在700 K时其最大ZT值达到049,与熔融+放电等离子体烧结试样相比提高了29%. 关键词： 熔体旋甩 n型InSb化合物 微结构 热电性能     

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.     

Thermal conductivity of ultrathin InSb semiconductor nanowires with properties of the Luttinger liquid

The thermal conductivity of ultrathin (～5 nm in diameter) and long (10 mm) InSb semiconductor quantum nanowires embedded in nanochannels of a dielectric chrysotile asbestos matrix is measured in the temperature range 5–300 K. The possible manifestation of the spin-charge separation of current carriers in these nanowires is discussed, which would provide an additional argument for the InSb nanowires possessing properties of the Luttinger liquid.     

Ballistic transport and quantum interference in InSb nanowire devices

An experimental realization of a ballistic superconductor proximitized semiconductor nanowire device is a necessary step towards engineering topological quantum electronics. Here, we report on ballistic transport in In Sb nanowires grown by molecular-beam epitaxy contacted by superconductor electrodes. At an elevated temperature, clear conductance plateaus are observed at zero magnetic field and in agreement with calculations based on the Landauer formula. At lower temperature, we have observed characteristic Fabry–Pérot patterns which confirm the ballistic nature of charge transport.Furthermore, the magnetoconductance measurements in the ballistic regime reveal a periodic variation related to the Fabry–Pérot oscillations. The result can be reasonably explained by taking into account the impact of magnetic field on the phase of ballistic electron's wave function, which is further verified by our simulation. Our results pave the way for better understanding of the quantum interference effects on the transport properties of In Sb nanowires in the ballistic regime as well as developing of novel device for topological quantum computations.     

Stimulated Emission at a Wavelength of 2.86 μm from In(Sb,As)/In(Ga,Al)As/GaAs Metamorphic Quantum Wells under Optical Pumping

JETP Letters - Metamorphic laser heterostructures In(Sb, As)/In0.81Ga0.19As/In0.75Al0.25As with InSb/InAs/InGaAs composite quantum wells based on submonolayer InSb insertions in a 10-nm InAs layer...