InSb Surface Research Articles

Control of the intensity of a single harmonic generated in laser plasma by varying the chirp of intense femtosecond pulses

A significant increase, as well as a decrease, in the intensity of single higher harmonics of femtosecond radiation of a Ti:sapphire laser that are generated in a weakly excited laser plasma on the surface of GaAs, Cr, InSb, In, and stainless steel is demonstrated. The intensities of some higher harmonics in different regions of their plateaulike distribution varied from a 23-fold excess over the intensity of the neighboring harmonics to the complete absence in the extreme ultraviolet spectrum. The specific features of a 200-fold increase in the intensity of the 13th harmonic generated in indium plasma are analyzed. These variations in the intensity distribution of harmonics in the plateau region are obtained by varying the chirp of laser pulses.

Quantum Hall effect at cleaved InSb surfaces and low-temperature annealing effect

The authors have performed low-temperature in-plane magnetotransport measurements on two-dimensional electron systems induced by deposition of Ag at in situ cleaved surfaces of p-type InSb. The quantum Hall effect was observed even at low magnetic fields around 2T. The surface electron density and the electron mobility exhibit strong dependence on the Ag coverage and the annealing temperature in the range of 15–40K. The annealing effect suggests that the surface morphology strongly affects the properties of the two-dimensional electron systems.

Excitation spectra of terahertz emission from semiconductor surfaces

Spectral dependences of THz radiation from laser-illuminated surfaces of InAs and InSb have been investigated experimentally at high optical fluences for laser wavelengths ranging from 0.6μm to 2μm. Efficient THz generation was discovered in the excitation range around 1.6μm. The influence of inter-valley scattering was evident. The energy position of subsidiary conduction band valleys was evaluated to be equal to 1.08eV and 0.53eV for InAs and InSb, respectively.

Adsorption of Metal-Free Phthalocyanine on InSb and InAs(001)-4 × 2/c(8 × 2) Surface

We have studied the adsorption of metal-free phthalocyanine on 4 x 2/c(8 x 2) surface reconstruction of both InSb(001) and InAs(001) surfaces, by means of low-energy electron diffraction and high-resolution electron energy loss spectroscopy. We show that the molecule-surface interaction is stronger in the case of the InAs substrate as compared to the InSb one. Indeed, we observed that at full monolayer coverage, when the molecules are adsorbed on the InAs, and only in that case, there are substantial energy shifts of both the substrate surface plasmon and the first valence exciton of the molecules. These shifts are evidence of charge transfer from the molecules toward the substrate responsible for a strong molecule-substrate interaction such as chemisorption. In spite of the difference between the two substrates, at monolayer completion, H 2 Pc on InAs and InSb adopts a common (4n x 3) surface arrangement. The same that was already reported for the nonplanar lead and tin phthalocyanines (respectively, PbPc and SnPc) adsorbed on InSb(001).

PTCDA molecules on an InSb(001) surface studied with atomic force microscopy

PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) molecular structures assembled on an InSb(001)c(8 × 2) reconstructed surface have been studied using frequency modulated atomic forcemicroscopy. The high-resolution imaging of the structures is possible through repulsiveinteractions, using the constant height scanning mode. During initial stages ofgrowth the [110] diffusion channel dominates as indicated by formation of longPTCDA molecular chains parallel to the [110] crystallographic direction on the InSbsurface. For a single monolayer coverage a wetting layer of PTCDA is formed.Finally it is shown that the PTCDA/InSb is a promising system for buildingmolecular nanostructures by manipulation of single molecules with the AFM tip.

Desorption of InSb(001) native oxide and surface smoothing induced by low temperature annealing under molecular hydrogen flow

The preparation of InSb (001) oxygen-free surfaces by thermal annealing at relatively low temperatures under molecular hydrogen flow is reported. This process is compared with thermal oxide desorption (TOD) at 400°C under ultrahigh vacuum conditions. Molecular hydrogen cleaning (MHC) at substrate temperature of 250°C and at hydrogen pressure of 5×10−6Torr resulted in complete desorption of the native oxide layer. Furthermore, no carbon contamination was observed on the surface following this treatment. The surface morphology of the samples following this process was found to be very smooth without any droplet structure. The In:Sb surface stoichiometry was nearly 1:1 along the MHC process. In addition, annealing the sample at 400°C in vacuum after oxide removal by MHC maintains the smoothness and the stoichiometry of the surface. In contrast, TOD at 400°C of an oxidized InSb surface in vacuum does not result in complete oxide removal from the surface. Furthermore, small droplets associated with In are produced at this annealing temperature. The surface stoichiometry shows In enrichment after TOD in vacuum above 360°C. The surface composition and chemical bonding were monitored by Auger electron spectroscopy and x-ray photoelectron spectroscopy as a function of process parameters. The surface morphology was analyzed by atomic force microscopy.

Metal nanostructures assembled at semiconductor surfaces studied with high resolutionscanning probes

Dynamic force microscopy (DFM), Kelvin probe force microscopy (KPFM) andscanning tunnelling microscopy/spectroscopy (STM/STS) have been used to studyepitaxial nanostructures formed as a result of submonolayer deposition of gold onreconstructed InSb, InAs, and GaAs(001) surfaces. It has been found that bothtopography and composition of the structures are strongly dependent on the substratetemperature during evaporation. In the particular case of Au deposited on a c(8 × 2) InSb(001) surface at 300 K, the nanostructures have predominantly the form ofrectangular islands with edges oriented along [110] and [] directions. Increasing the substrate temperature up to 600 K during deposition resultsin formation of narrow, long structures (nanowires) with an average length of800 nm. The nanowires are created along the [110] direction of the reconstructedInSb(001) surface. High resolution KPFM and STS measurements indicate thatnanowires of different heights may have different chemical composition and electronicstructure.

Structure and composition of chemically prepared and vacuum annealed InSb(0 0 1) surfaces

The InSb(0 0 1) surfaces chemically treated in HCl–isopropanol solution and annealed in vacuum were studied by means of X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and electron energy-loss spectroscopy (EELS). The HCl–isopropanol treatment removes indium and antimony oxides and leaves on the surface about 3 ML of physisorbed overlayer, containing indium chlorides and small amounts of antimony, which can be thermally desorbed at 230 °C. The residual carbon contaminations were around 0.2–0.4 ML and consisted of the hydrocarbon molecules. These hydrocarbon contaminations were removed from the surface together with the indium chlorides and antimony overlayer. With increased annealing temperature, a sequence of reconstructions were identified by LEED: (1 × 1), (1 × 3), (4 × 3), and (4 × 1)/c(8 × 2), in the order of decreasing Sb/In ratio. The structural properties of chemically prepared InSb(0 0 1) surface were found to be similar to those obtained by decapping of Sb-capped epitaxial layers.

Surface reactivity of InSb studied by cyclic voltammetry coupled to XPS

The surface chemistry of InSb was modified by anodic treatment at different pH. Using a coupled approach based on electrochemical and surface analysis techniques we determined different chemical configurations for the oxidized InSb surface. Sb-rich oxidized surfaces or stoichiometric ones have been obtained.

Oxide-free InSb (100) surfaces by molecular hydrogen cleaning

We report that annealing of an oxidized InSb (100) single-crystal sample at 250°C under molecular hydrogen flow [molecular hydrogen cleaning (MHC)] results in complete desorption of the surface oxides. Following this process, the surface morphology is found to be very smooth at the nanometric scale without any droplet structure and a nearly 1:1 In:Sb stoichiometry. MHC was applied to remove the native oxide of an epi-ready InSb(100) substrate used for molecular beam epitaxy growth of InSb films. These results suggest that MHC of InSb can be used as a very effective cleaning process for epitaxial film growth.

Molecular beam epitaxy and morphological studies of homoepitaxial layers on chemical mechanical polished InSb(100) and InSb(111)B substrates

Noncontact atomic force microscopy (AFM) has been used to assess the surface morphology and structure of InSb homoepitaxial layers grown on chemical mechanical polished (CMP) InSb(100) and InSb(111)B surfaces. Although it is difficult to grow epilayers on highly conducting InSb substrates, this work demonstrates the ability to grow layers with an average roughness (Ra) of 5.7Å on 2×1018 n-type InSb(100) surfaces. Furthermore on 7×1014 n-type InSb(111)B surfaces, extremely flat layers with Ra’s of approximately 1.7Å were grown. Thermal x-ray photoelectron spectroscopy was implemented to analyze surface oxide desorption on the CMP prepared “epiready” wafers. Sb to In flux ratio and substrate deposition temperature are critical in obtaining high quality epitaxial material. For the InSb(100) surfaces, an Sb∕In flux ratio of 1.5:1, a substrate temperature of 380°C, and a background pressure of 1×10−10Torr produced smooth surfaces. For InSb(111)B surfaces, a ratio of 7:1 and a substrate temperature of 380°C at a similar background pressure produced smooth surfaces. Higher flux ratios resulted in atomically rough surfaces. The homoepitaxy formation of an ordered step terrace surface was confirmed with AFM on both epiready CMP prepared InSb crystal surfaces.

Electron States and Elementary Excitations at Semiconductor Surfaces Controlled by Adsorption

Adsorption on a doped semiconductor surface often induces a gradual formation of a carrier-depletion or carrier-accumulation layer at the surface, which has a great influence on the surface electronic excitations often coupled with surface optical phonons in compound semiconductors. Firstly, we give a brief survey of formation of depletion layers at n-type GaAs and InSb surfaces and of accumulation layers at n-type InAs surfaces. Secondly, we describe how the subband structure varies in an accumulation-layer formation process at an n-type InAs(110) surface, with special emphasis on the growing influence of nonparabolicity of the conduction-band dispersion. Finally, we elucidate the evolution of surface elementary excitations, namely, two coupled plasmon-phonon modes at the surface and a surface optical-phonon mode involving screening charges, in a depletion-layer formation process at an n-type GaAs(110) surface. Our systematic analysis provides a clear explanation of the change in the electron energy-loss spectrum.

Cleaning InSb wafers for manufacturing InSb detectors

Three chemical cleaning procedures for InSb(111) wafers were studied. X-ray photoelectric spectroscopy, and scan electron microscope were used to assess their credibility for use in manufacturing the InSb detectors. It is shown, a suitable thermal treatment can remove In oxide and Sb oxide and therefore, all procedures approach to similar results from this point of view. But undulation and peel-like features has been observed on InSb(111) surface etched by all etchants except a modified CP4A etchant (HNO 3 :CH 3 COOH:HF:H 2 O at 2:1:1:10). Also control the etch rate and etching process can be done better in CP4A than the others. The XPS results show different spectra for SbO x and InO x when, InSb(111) is compared with InSb(100) and it means that, for different crystal orientation and different etchant there are different cleaning method for removing SbO x and InO x . Finally the effect of etchants on the performance of InSb detectors was shown.

Spectral dependencies of terahertz emission from InAs and InSb

Spectral dependences of the THz radiation from the laser-illuminated surfaces of InAs and InSb have been investigated experimentally at high optical fluences for the laser wavelengths ranging from 0.6 to 2μm. Efficient THz generation was discovered in the excitation range around 1.6μm. The influence of the intervalley scattering was clearly evidenced. The energy position of the subsidiary conduction band valleys was evaluated from this study to be equal 1.08 and 0.53 eV for InAs and InSb, respectively. It has been concluded that THz emission at high excitation fluencies is dominated by the shift current effect.

Self-assembled monolayer of tin-phthalocyanine on InSb(0 0 1)-(4 × 2)/c(8 × 2)

We have herein studied the adsorption of tin-phthalocyanine on the indium rich 4 × 2/c(8 × 2) reconstruction of the InSb(0 0 1) surface, using scanning tunneling microscopy, low-energy electron diffraction and high-resolution electron energy loss spectroscopy. The tin-phthalocyanine molecules form a stable monolayer with a characteristic long-range one-dimensional order, imposed by the twofold symmetry of the substrate surface reconstruction. High-resolution electron energy loss studies of both the vibrational and the electronic eigenmodes of the molecules show that phthalocyanines lie flat on the surface. In that, they behave the same way as lead phthalocyanines, which leads us to suggest that a common adsorption configuration may be adopted by non-planar phthalocyanines on the InSb(0 0 1)-4 × 2/c(8 × 2) surface.

Epitaxial nanostructures assembled on InSb(0 0 1) by submonolayer deposition of gold

Nanostructures formed during submonolayer deposition of gold on clean c(8 × 2)InSb(0 0 1) surface in ultrahigh vacuum have been investigated with dynamic force microscopy (DFM) and Kelvin probe force microscopy (KPFM). It is found that gold structures have predominantly the form of rectangular islands with edges oriented along 〈1 1 0〉 and 〈1 −1 0〉 directions and their average size is dependent on the substrate temperature during evaporation. Upon annealing the initial rectangular shape of the islands is preserved but their average size is almost doubled. Furthermore, KPFM chemical imaging of the islands evidences that their composition is different from the composition of the homogeneous substrate. In addition, the change of the low energy electron diffraction pattern from c(8 × 2) to c(4 × 4) strongly suggests that the substrate surface between the islands has been converted from In-rich to Sb-rich, most likely due to alloying of the surface indium with gold in the islands.

Transport properties of InSb and InAs thin films on GaAs substrates

The heterointerfaces in InAs and InSb thin films grown on GaAs were found to affect the temperature dependence of the film's electrical properties such as electron mobility, electron density, and resistivity. The InAs and InSb surfaces of the films, which act as heterointerfaces with air, were found to similarly affect the electrical properties. It was found that the electron mobility of both InAs and InSb films grown on GaAs substrates has a three-layer structure.

Reflected electron energy loss microscopy (REELM) studies of metals, semiconductors and insulators

The potential of reflected electron energy loss microscopy (REELM) are tested in surface and interface studies of metals, semiconductors and insulators. We present spectroscopic analyses of loss signals occurring at ∼5–30 eV of the elastic peak, and microscopic analyses based on the same signals performed via spot mode, as well as via linescanning and imaging modes. Materials investigated include a UHV cleaved InSb surface, InP/SiO 2 and GaAs/Au systems, W tips for use in an STM microscope, a ZrO 2 single crystal, and an archaeological bronze covered with a thick patina. Advantages and shortcomings of REELM are outlined against the diagnostic value of parallel results obtained by scanning Auger microscopy (SAM) techniques. Although comparatively poor focussing powers preclude the attainment of high spatial resolution, and spectral interference problems may hinder the chemical characterization of multi-phase materials, REELM features unique capabilities. Among others, these include a chemical contrast that is much superior to that of SAM, the possibility of characterizing the coverage distribution of adlayer surface species, as well as of investigating the microchemistry of insulators’ surfaces. The first application of REELM in the analysis of archaeological materials is presented.

Spin-orbit effects on reflectance anisotropy spectroscopy

We study the effects of the spin-orbit coupling on the reflectance anisotropy spectroscopy of semiconductor surfaces. A microscopic formulation based on a semi-empirical tight binding approach which includes spin-orbit interaction is used and theoretical results are obtained for clean $(110)1\ifmmode\times\else\texttimes\fi{}1$ surfaces of GaAs, InAs, and InSb. We show that the changes due to the spin-orbit coupling on the reflectance anisotropy gives spectra that compares rather well with the experimental results.

Growth monitoring of GaAsSb:C/InP heterostructures with reflectance anisotropy spectroscopy

Using time-resolved reflectance anisotropy spectroscopy (RAS) we studied in situ the dynamics of surface processes of Sb-covered GaAs(1 0 0) and InP(1 0 0) under metalorganic vapour-phase epitaxy conditions. Both Sb removal during a hydride purge and Sb incorporation during GaAs and InP overgrowth were monitored enabling the investigation of group V exchange reactions. Sb surface layers are found to be much more stable during purge with PH 3 as compared to AsH 3. Estimated activation energies are 2.5 eV for the Sb–P exchange processes and 1.1 eV for the Sb–As exchange reactions. These values reflect the low volatility of Sb compared to other group V adsorbates. During InP overgrowth Sb is rapidly buried at temperatures of 510 °C and below while it is rather persistent on the surface at temperatures of 550 °C and above. This transition indicates the existence of a highly mobile quasi-liquid InSb surface layer at temperatures above its melting point (∼525 °C).