InSb Surface Research Articles

Femtosecond laser-induced ultrafast electron dynamics and band gap renormalization in InSb

Studying ultrafast dynamical processes is essential for understanding light-matter coupling, which is crucial for the optoelectronic and photonic applications of semiconductor materials. Herein, we investigate the evolution of electron population near the conduction band minimum (CBM) and band gap in InSb (100) crystal under different laser fluences using time- and angle-resolved photoelectron spectra (TrARPES). In contrast to the pump-fluence-independent fast growth process (FP) of the electron population, the slow process (SP) is fluence sensitive, which is similar to the temperature-dependent behavior observed in InSb (110). In addition, we observe a band gap enlargement with increasing the photoexcitation flux. Comprehensive analysis reveals that these observed diverse results are attributed to the laser-tunable dielectric function on the surface of InSb. Our findings not only enhance the understanding of laser-semiconductor interactions but also broaden the potential applications in the field of optoelectronic and photonic devices.

Dry cleaning of InSb surfaces by hydrogen molecule exposure in ultrahigh vacuum

Cleaning semiconductor surfaces by atomic hydrogen or hydrogen plasma has gained significant interest because such a dry-cleaning method enables to reduce consumption of chemicals and pure water, and to treat challenging surfaces of three-dimensional semiconductor nanostructures. We have studied effects of mere H2 molecule exposures on (111)B and (110) surfaces of InSb with native oxides in an ultrahigh-vacuum (UHV) chamber. Without any hydrogen cracking, exposure of native-oxide covered InSb(111)B, heated simultaneously at 350 °C, to H2 with a partial pressure of 5∙10−5 mbar decreases amount of surface oxides and carbon, according to x-ray photoelectron spectroscopy, and provides (2×2) low-energy electron diffraction (LEED) pattern. Scanning tunneling microscopy indicates that this InSb(111)B(2×2) surface contains still extra Sb. When the InSb temperature increases to 400 °C during the H2 exposure, LEED changes to (3×3) pattern, which is known to arise from a less Sb-rich surface compared to InSb(111)B(2×2). When InSb(111)B(3×3) is exposed to H2 at the lowered temperature of 300 °C, LEED changes back to (2×2), which is discussed to arise from that InSb(111)B(3×3) contains still oxygen. Experiments for InSb(110) support that the found H2 exposure effects apply to different crystal faces of InSb.

Atomic structure of In2O3 films on InSb nanowire and nanosheet

Surface reactions of indium antimonide (InSb) nanowires and nanosheets, including oxidation, often result in the performance deterioration of semiconductor devices. In this study, we characterized the oxide films of InSb nanowires/nanosheets at the atomic level. The oxide film on the nanowire is composed of In2O3, which grows in islands and layers along the (1¯11) and (002) planes of the matrix. The oxide film on the lateral side of the InSb nanosheet was amorphous and thinner than the oxide film on the nanowire. In2O3 grew via the external diffusion of indium ions. The oxide films on the InSb nanowires and nanosheets are closely related to the InSb surface features.

Electronic structure of InSb (001), (110), and (111)B surfaces

The electronic structure of various (001), (110), and (111)B surfaces of n-type InSb was studied with scanning tunneling microscopy and spectroscopy. The InSb(111)B (3×1) surface reconstruction is determined to be a disordered (111)B (3×3) surface reconstruction. The surface Fermi-level of the In rich and the equal In:Sb (001), (110), and (111)B surface reconstructions was observed to be pinned near the valence band edge. This observed pinning is consistent with a charge neutrality level lying near the valence band maximum. Sb termination was observed to shift the surface Fermi-level position by up to 254±35 meV toward the conduction band on the InSb (001) surface and 60±35 meV toward the conduction band on the InSb(111)B surface. The surface Sb on the (001) can shift the surface from electron depletion to electron accumulation. We propose that the shift in the Fermi-level pinning is due to charge transfer from Sb clusters on the Sb terminated surfaces. Additionally, many subgap states were observed for the (111)B (3×1) surface, which are attributed to the disordered nature of this surface. This work demonstrates the tuning of the Fermi-level pinning position of InSb surfaces with Sb termination.

Effect of growth temperature and Sb over in flux ratio on the Bi content and the surface morphology of InSbBi grown by molecular beam epitaxy

We investigated the effect of VSb/IIIIn flux ratio and growth temperature on the Bi content of InSbBi material grown on an InSb substrate using molecular beam epitaxy. The Rutherford backscattering spectrum from a bulk InSb0.977Bi0.023 epitaxial film showed a 98.5% substitutional site incorporation of Bi atoms. We demonstrated that a kinetic model of the growth can accurately predict the Bi content by taking into account the extremely low desorption/hopping probability of Sb on the InSb surface due to its low growth temperature and weaker In-Bi bond. The model implies a Bi desorption energy barrier on the InSb surface and an activation energy for Sb to displace Bi of 1.27 eV and 0.29 eV, respectively.

Field effect two-dimensional electron gases in modulation-doped InSb surface quantum wells

We report on transport characteristics of field effect two-dimensional electron gases (2DEGs) in surface indium antimonide quantum wells. The topmost 5 nm of the 30 nm wide quantum well is doped and shown to promote the formation of reliable, low resistance Ohmic contacts to surface InSb 2DEGs. High quality single-subband magnetotransport with clear quantized integer quantum Hall plateaus is observed to filling factor ν = 1 in magnetic fields of up to B = 18 T. We show that the electron density is gate-tunable, reproducible, and stable from pinch-off to 4 ×1011 cm−2, and peak mobilities exceed 24 000 cm2/V s. Large Rashba spin–orbit coefficients up to 110 meV ·Å are obtained through weak anti-localization measurements. An effective mass of 0.019me is determined from temperature-dependent magnetoresistance measurements, and a g-factor of 41 at a density of 3.6 ×1011 cm−2 is obtained from coincidence measurements in tilted magnetic fields. By comparing two heterostructures with and without a delta-doped layer beneath the quantum well, we find that the carrier density is stable with time when doping in the ternary Al0.1In0.9Sb barrier is not present. Finally, the effect of modulation doping on structural asymmetry between the two heterostructures is characterized.

Oxide desorption process from InSb surface under Sb flux

In this work, the process of oxide removal from the InSb (001) surface was studied in situ by high-energy electron diffraction in vacuum and under an antimony flux. The dependence of the oxide thickness on the annealing temperature was obtained. It has been found that the antimony flux slows down the process of oxide removal due to the oxide formation reaction. The oxide removal process was described by a system of kinetic equations, the activation energy of oxide decomposition was determined Keywords: InSb, oxide, activation energy, desorption.

Процесс десорбции оксида с поверхности InSb в потоке сурьмы

In this work, the process of oxide removal from the InSb (001) surface was studied in-situ by high-energy electron diffraction in vacuum and under an antimony flux. The dependence of the oxide thickness on the annealing temperature was obtained. It has been found that the antimony flux slows down the process of oxide removal due to the oxide formation reaction. The oxide removal process was described by a system of kinetic equations, the activation energy of oxide decomposition was determined.

Ion Irradiation Induce Surface Modifications of InSb(001)

Morphological development on InSb(001) surfaces, under ion irradiation, has been investigated by means of Atomic Force Microscopy in UHV conditions. The InSb(001) surface has been exposed to Ar+ beam with varying incident angles (from 0° to 80° off-normal) for energy 4.0 keV and fluence 4x1017 ion/cm2. Different kinds of nanostructures, depending on ion incident angle, have been observed on the irradiated surfaces such as nanocavities, or nanorings and nanodots, preferentially for close to normal incidence, and well-order ripples for the oblique incidence. The formation of ripple structures on InSb(001) surfaces as a function of the incidence angle has been observed. The orientation of the ripples has been found to be incident angle dependent and it is perpendicular, or parallel to the ion beam projection on the irradiated surface for angles of 45° and 80°, respectively.. The results have been discussed in terms of ballistic processes of sputtering and Bradley Harper theory for surface modifications.

Electronic Structure of InAs and InSb Surfaces: Density Functional Theory and Angle‐Resolved Photoemission Spectroscopy

AbstractThe electronic structure of surfaces plays a key role in the properties of quantum devices. However, surfaces are also the most challenging to simulate and engineer. Here, the electronic structure of InAs(001), InAs(111), and InSb(110) surfaces is studied using a combination of density functional theory (DFT) and angle‐resolved photoemission spectroscopy (ARPES). Large‐scale first principles simulations are enabled by using DFT calculations with a machine‐learned Hubbard U correction [npj Comput. Mater. 6, 180 (2020)]. To facilitate direct comparison with ARPES results, a “bulk unfolding” scheme is implemented by projecting the calculated band structure of a supercell surface slab model onto the bulk primitive cell. For all three surfaces, a good agreement is found between DFT calculations and ARPES. For InAs(001), the simulations clarify the effect of the surface reconstruction. Different reconstructions are found to produce distinctive surface states, which may be detected by ARPES with low photon energies. For InAs(111) and InSb(110), the simulations help elucidate the effect of oxidation. Owing to larger charge transfer from As to O than from Sb to O, oxidation of InAs(111) leads to significant band bending and produces an electron pocket, whereas oxidation of InSb(110) does not. The combined theoretical and experimental results may inform the design of quantum devices based on InAs and InSb semiconductors, for example, topological qubits utilizing the Majorana zero modes.

Scanning tunneling microscopy of strained-α-Sn(0 0 1) surface grown on InSb(0 0 1) substrate

We investigated the surface structure of strained-α-Sn layers grown on InSb(001) surfaces, which have been attracting the attention of the researchers in the field of topological materials, by optimizing the surface cleaning procedures of the InSb substrate surfaces and the growth conditions of the Sn layers. Accordingly, scanning tunneling microscopy observations showed that the (2 × 2) diffraction patterns are due to the double domain (2 × 1) reconstructed surfaces rotated 90° with respect to one another, as previously suggested based on diffraction observations.

Local structure of porous InSb films: From first to third-shell EXAFS investigation

Extended x-ray absorption fine structure spectroscopy was used to investigate the neighborhood of In and Sb atoms in InSb films deposited by magnetron sputtering and subsequently irradiated with 14 MeV Au+6 ions at room temperature, with ion fluences ranging from 1 × 1013 cm−2 to 2 × 1014 cm−2. For the first nearest-neighbor shell, the structural parameters were unaffected by ion irradiation up to 1 × 1014 cm−2. However, the irradiation-induced disorder was observed for the second and third nearest-neighbor shells through decrease (increase) of the coordination number (Debye-Waller factor). Upon ion irradiation, InSb films become porous while still retaining part of their crystallinity. Using x-ray absorption near edge structure, it was observed that In K-edge and Sb K-edge positions are unchanged as a function of ion fluence in InSb, evidencing that the energy of the element-specific unoccupied local states is independent of ion fluences used in this work. For the highest irradiation fluence (2 × 1014 cm−2), part of InSb is converted to In2O3, Sb2O3, Sb2O5 and metallic Sb, representing a fraction of ~26%, ~7%, ~11%, and ~9%, respectively. This increase in antimony and indium oxides at this irradiation fluence was attributed to the combination of the high reactivity, in the presence of oxygen, of the InSb surface with the enhanced surface-area-to-volume ratio of the porous structure.

Tunable tunnel barriers in a semiconductor via ionization of individual atoms

We report scanning tunneling microscopy (STM) studies of individual adatoms deposited on an InSb(110) surface. The adatoms can be reproducibly dropped off from the STM tip by voltage pulses, and impact tunneling into the surface by up to ∼100×. The spatial extent and magnitude of the tunneling effect are widely tunable by imaging conditions such as bias voltage, set current and photoillumination. We attribute the effect to occupation of a (+/0) charge transition level, and switching of the associated adatom-induced band bending. The effect in STM topographic images is well reproduced by transport modeling of filling and emptying rates as a function of the tip position. STM atomic contrast and tunneling spectra are in good agreement with density functional theory calculations for In adatoms. The adatom ionization effect can extend to distances greater than 50 nm away, which we attribute to the low concentration and low binding energy of the residual donors in the undoped InSb crystal. These studies demonstrate how individual atoms can be used to sensitively control current flow in nanoscale devices.

Improvement the InAs, InSb, GaAs and GaSb surface state by nanoscale wet etching

Various experimental approaches of the wet nanoscale treatment have been proposed to account for features of the InAs, InSb and GaAs, GaSb semiconductor dissolution process in the (NH4)2Cr2O7–HBr–EG etching solution. Etching kinetics data showed that a crystal dissolution has diffusion-determined nature. The lowering of the solvent concentration from 80 to 0 vol.% in the solution was accompanied by a significant increase in the semiconductor etching speed. Depending on the solution composition, we have studied two types of crystal surface morphology, polished and passivated by the film, which was formed after chemical-dynamic (CDP) and/or chemical-mechanic polishing (CMP) in the solution, saturated by solvent and by oxidant, accordingly. It was found that in the polished etchants both CDP and CMP procedures lead to the formation of the mirror-like and super-smooth surface with nanoscale roughness less than 1 nm. The obtained results of surface state indicate that the (NH4)2Cr2O7–HBr–EG etchants could be used successfully for controllable CDP and CMP treatment of III–V semiconductors and formation of super-smooth surface.

Terahertz Nonreciprocal Isolator Based on Magneto-Plasmon and Destructive Interference at Room Temperature

A terahertz isolator is demonstrated for the THz nonreciprocal reflections in the magneto-optical microstructure composed of InSb and metasurface with a dielectric interlayer. In the Voigt magnetic field configuration, the reflectance of the p-polarization waves obliquely impinging on the InSb wafer exhibits high nonreciprocity, while the reflectance of the s-polarized wave is reciprocal. Based on the unique magneto-plasmonic modes on the InSb surface, the nonreciprocal reflection in this device can be enhanced by using the destructive interference between the direct reflection and the multiple reflections in the resonance cavity between the InSb and metasurface. After the optimization, the isolation power of the device exceeds 55 dB with the insertion loss of only −3.92 dB under a very weak magnetic field of 0.2 T at room temperature. More importantly, the introduction of the metasurface can reduce the operating frequency of the isolator from 2.434 THz to 2.136 THz. This low-loss, weak magnetic field, room temperature operating, and high isolation THz isolator shows its broad potential in THz application systems.

Effect of Oxygen and Fluorine Absorption on the Electronic Structure of the InSb(111) Surface

The binding energy of oxygen and fluorine on the InSb(111) surface is investigated as a function of the termination of the latter using the projector augmented-wave method. It is shown that fluorine adsorption on the In-terminated surface leads, depending on the fluorine concentration, to the complete or partial elimination of the surface states induced by oxygen adsorption from the forbidden gap. The penetration of both adsorbates into the subsurface layers leads to the breaking of In–Sb bonds and the formation of chemical bonds of fluorine and oxygen with surface substrate atoms, which is the initial stage of the formation of a fluorine-containing anodic oxide layer. On the Sb-terminated InSb(111) surface, oxygen adsorption facilitates a decrease in the surface-state density in the forbidden gap. General trends in the variation in the electronic structure of the (111) surface upon fluorine and oxygen coadsorption in III–V semiconductors are discussed.

Влияние адсорбции кислорода и фтора на электронную структуру поверхности InSb(111)

The projector augmented-wave method was used to study the energetics of oxygen and fluorine bonding on the InSb(111) surface depending on its termination. It is shown that the fluorine adsorption on the In-terminated surface depending on its concentration leads to a partial or complete removal of surface states induced by oxygen adsorption from the forbidden gap. Penetration of both adsorbates into subsurface layers results in breaking of In–Sb bonds and the formation of chemical bonds of fluorine and oxygen with subsurface atoms of the substrate. It is the initial stage of the formation of a fluorine-containing anode oxide layer. In the case of the InSb(111) surface terminated by antimony, oxygen adsorption contributes to a decrease in the density of surface states in the forbidden gap. The general trends in the changes of the electronic structure of the (111) surface during the fluorine and oxygen coadsorption are discussed in a set of III–V semiconductors.

Gallium-assisted growth of InSb nanowire

Indium antimony (InSb) nanowires have been synthesized by chemical vapor deposition and we found that adding gallium as the other evaporation resource can increase the density of nanowires and no doping pollution. For the growth of InSb nanowire, Au film was annealed to form Au nanoparticles as catalysts and explain its catalytic principle. We thought that gallium which coated on the surface of Au nanoparticles assisted nucleation and growth of InSb nanowire in the early stage. The diameter of the InSb nanowires was 60–100nm and 1-5μm in length. The grown nanowires have good crystallinity. We found that the surface of InSb was oxidized, and the main oxide was indium oxide. We discovered the tip morphologies of nanowires are different and discussed the causes of this phenomenon in detail.

Epitaxial growth and electronic properties of few-layer stanene on InSb (1 1 1)

Stanene has been theoretically predicted to be a 2D topological insulator with a large band gap, potentially hosting quantum spin Hall effect at room temperature. Here, few-layer stanene films have been epitaxially grown on Sb-terminated InSb (1 1 1) surface and their structural and electrical properties are characterized. Scanning tunneling spectrum results reveal a large bulk bandgap in single-layer stanene (over 0.2 eV). Moreover, spectroscopy evidence for a filled edge state near the steps was observed. The gap decreases dramatically with increasing number of layers, and multilayer stanene should become a Dirac semimetal in the bulk limit. The changeover may involve nontrivial topological phase transitions. Clear and reproducible Shubnikov–de Haas oscillations were observed on the single-layer stanene films that were exposed to atmospheric conditions for an extended period of time, showing the possibility for device experiments using nanofabrication and magneto-transport. Our results demonstrate that the single-layer stanene is a promising topological material for exploring fundamental physics and quantum applications.

Influence of fluorine and oxygen atom adsorption on electronic structure of InSb(111) surface

The projector augmented-wave method was applied for investigation of oxygen and fluorine atom adsorption on the InSb(111) surface depending on its termination. It was shown that oxygen adsorption leads to appearance of additional surface states in the fundamental gap in case of the In-terminated surface while the density of surface states decreases for the Sb-terminated surface. Fluorine co-adsorption results in partial or complete removal of the surface state and an unpinning of the Fermi level. The increase of fluorine concentration leads to considerable changes of the near-surface-layer structure due to the penetration of both electronegative adsorbates (O and F) into the substrate.