InSb Films Research Articles

Weak-field magnetoresistance anomaly and Shubnikov–de Haas oscillations in Sn-doped InSb thin films on GaAs (100) substrates

Distinctive magnetoresistance (MR) effects in weak magnetic fields before the appearance of Shubnikov–de Haas (SdH) oscillations at low temperatures in Sn-doped (7×10 16 cm −3) InSb films grown on GaAs(100) substrates by MBE have been investigated with decreasing film thickness d from 1 μm . The negative MR found in weak magnetic fields for d⩾0.5 μm can be broadly divided into two regimes: T-sensitive negative MR below B c observed with anisotropy between parallel and perpendicular magnetic field and a T-insensitive parabolic one above B c observable only under in-plane magnetic fields. The latter is ascribable to the skipping orbit effect due to surface boundary scattering. In vanishing magnetic fields far below B c, the negative MR reduces with decreasing d and the different positive MR overlaps with it below 0.5 μm , eventually dominating the positive MR at d∼0.2 μm . These results have been analyzed using a two-layer model for the films, where the composition of the upper layer under the surface and the lower one adjacent to the InSb/GaAs interface is assumed. The MR data in the extremely weak magnetic fields below 100 G for each layer have been successfully fitted to the two-dimensional (2D) weak localization (WL) theory. These results explain that the crossover from the 2D WL to the weak anti-localization (WAL) occurs when the interface is approached with the increase of SO interaction in the layers caused by the increased influence of the asymmetric potential at the hetero interface (Rashba term) and the SO rate in the intrinsic InSb film due to the crystal field of the zinc-blende structure (Dresselhaus term) is as small as τ so −1⩽3×10 8 s −1 .

Heteroepitaxial growth of InSb films on a Si(0 0 1) substrate via AlSb buffer layer

AlSb is a more suitable material as buffer layers for the heteroepitaxial growth of InSb films on a Si(0 0 1) substrate than Ge. It reduces the large lattice mismatch of about 19.3% between Si and InSb to about 5.6%. The resistance of AlSb with stoichiometric composition is large enough for the measurement of electrical properties. InSb films grown on the AlSb/Si(0 0 1) substrates by the co-evaporation of elemental indium (In) and antimony (Sb) sources were characterized by Auger electron spectroscopy (AES), X-ray diffraction (XRD) and atomic force microscopy (AFM), as a function of growth temperature. The thickness of grown InSb films was about 0.8–1.0 μm. The surface morphology and the crystal quality of the grown films strongly depend on growth temperature. It is found that the optimized growth temperature is about 300 °C to obtain the InSb films with smooth surface and good crystal quality.

Low-temperature transport properties of InSb films on GaAs(1 0 0) substrates

Low-temperature magnetoresistance (MR) has been studied for undoped and Sn-doped InSb thin films grown on GaAs(1 0 0) substrates by MBE. Sn-doped films show the Shubnikov–de Haas oscillations which reflect a large g-factor ( g ∗∼−40 depending on the carrier concentration) of electrons in InSb films. In undoped films, on the other hand, almost whole carriers fall into the accumulation layer at the InSb/GaAs interface at low temperatures, resulting in the advent of positive MR arising from the two-dimensional weak anti-localization due to spin–orbit interaction.

Transport properties of Sn-doped InSb thin films and applications to Hall element

The temperature dependence of the transport properties of undoped and Sn-doped InSb single crystal thin films grown on GaAs substrates by MBE were investigated. The temperature dependence of undoped InSb thin films was large and had maximum near room temperature, whereas the Sn-doped thin films showed very small and monotonic decrease with increasing temperature. The electron mobility of the films varied significantly in the growth direction from the InSb/GaAs hetero-interface to the InSb thin film surface. This large variation of the electron mobility in the growth direction explained the observed temperature dependence of the electron mobility for these films. The large variation of the electron mobility in the growth direction was described by a simple model of two layers with a low electron mobility layer near the hetero-interface and the other with a high electron mobility. These InSb films were used to fabricate practical and highly sensitive Hall sensors with a very small temperature dependence.

Weak localization in InSb thin films heavily doped with lead

We study the weak localization (WL) in three-dimensional polycrystalline thin films of InSb. The films are closely compensated showing the electron concentration $n>{10}^{16} {\mathrm{cm}}^{\ensuremath{-}3}$ at the total concentration of the donor- and acceptor-type structural defects ${N}_{t}>{10}^{18} {\mathrm{cm}}^{\ensuremath{-}3}.$ Unless Pb doped, the InSb films do not show any measurable or show very small WL effect at 4.2 K. The Pb doping to the concentration of the order of ${10}^{18} {\mathrm{cm}}^{\ensuremath{-}3}$ leads to pronounced WL effects below 7 K. From the comparison of the experimental data on temperature dependence of the magnetoresistivity and sample resistance with the WL theory, the dependence of the phase destroying time ${\ensuremath{\tau}}_{\ensuremath{\varphi}}(T)$ is determined. It is concluded that the dephasing is connected to three separate processes. The first is due to the spin-orbit scatterings and is characterized by temperature-independent relaxation time ${\ensuremath{\tau}}_{\mathrm{so}}\ensuremath{\simeq}{10}^{\ensuremath{-}12} \mathrm{s}.$ The second is associated with the electron-phonon interaction $({\ensuremath{\tau}}_{i}\ensuremath{\sim}{T}^{\ensuremath{-}3}).$ The third dephasing process is characterized by temperature-independent relaxation time ${\ensuremath{\tau}}_{c}=(1--7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12} \mathrm{s},$ which is tentatively ascribed to inelastic scattering at extended structural defects. The resulting time ${\ensuremath{\tau}}_{\ensuremath{\varphi}}$ shows saturation in its temperature dependence for $\stackrel{\ensuremath{\rightarrow}}{T}0.$ The temperature dependence of the resistance can be explained by the electron-electron interaction for $T<1 \mathrm{K},$ and by the WL effect for $T>2 \mathrm{K}.$

Synthesis of InSb Films by Reduction of Metal Alkoxide-Derived InSbO4.

A new synthetic route based on a solution chemistry was developed for a compound semiconductor indium antimonide (InSb). Considering the moisture sensitive properties of metal alkoxides, indium antimonide was synthesized by reduction of InSbO4, which was prepared by hydrolysis of the corresponding metal alkoxides as starting materials. InSb-alkoxide solution was prepared by two ways: one is mixed method in which In-alkoxide solution and Sb-alkoxide solution were mixed simply, and the other is continuous method using the reaction of indium chloride with Na-alkoxide in the presence of Sb-alkoxide in ethanol. Hydrolysis products by both methods were crystallized to InSbO4 by heat-treatment at 780°C in air. InSb was obtained by heat-treatment of hydrolysis product prepared by the continuous method at 400°C in H2, but it wasn't obtained from hydrolysis product prepared by the mixed method. The primary particle size of hydrolysis products was about 8nm in diameters. The wet hydrolysis product was well mixed with ethylcellulose and terpineol by a three-roll mill to form printing paste. The paste was screen-printed on slide glass substrates, transformed to InSb film by heat treatment at 400°C in H2.

Twinned InSb molecular layer on Si([formula omitted]) substrate

We studied the formation of a twinned InSb molecular layer on Si(111) substrate (epitaxial relation InSb[112]∥Si[110]) by depositing 1-ML Sb on Si(111)–In(4×1) reconstruction at 210°C, using reflection high-energy electron diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy. Sb adsorption replaces Si–In bonds in the In(4×1) reconstruction and forms Si–Sb bonds. Codeposition of In and Sb on the Si(111)-7×7 surface results in the formation of an InSb film with no twin (epitaxial relation InSb[110]∥Si[110]). Annealing this twinned InSb layer above 350°C resulted in the formation of Si(111)–Sb(3×3) structure, and the coalescence of most of the In. However, direct Sb deposition on Si(111)-7×7 at 350°C results in only disordered phase. Softening of the Si/Sb interface by the Si–In and In–Sb reactions is proposed to be responsible for the formation of the InSb twinned layer (at 210°C) and 3×3 structure by Sb (at 350°C).

How Si([formula omitted])–4×3-In reconstruction improves the epitaxial quality of InSb films grown on Si([formula omitted]) substrates

Direct growth of InSb on Si(001) substrate is difficult due to 19.3% mismatch between Si and InSb. However, we could grow high-quality InSb films on Si(001) substrates by predepositing a Si(001)–4×3-In reconstruction. The present report illustrates how the improvement in the growth is directly related to the 4×3 structure of the In reconstruction and its stability against Sb adsorption. These results clearly show that Sb adsorption does not replace the In(4×3) reconstruction below 300°C.

Growth of high-quality InSb films on Si(1 1 1) substrates without buffer layers

Molecular beam epitaxial growth of InSb on Si(1 1 1)7×7 surface is performed in the temperature range, 170–400°C. Epitaxial growth is achieved by suitably adjusting the growth rate, In/Sb flux ratio and substrate temperature. For growth temperatures up to 300°C surface morphology and the epitaxial quality of the film improve with temperature, whereas above 300°C, an increase in growth temperature deteriorates the epitaxial growth. Hall measurements reveals that the electron mobility of the film increases with growth temperature and for the film grown at 300°C it is about 2200 cm 2 V −1 s −1 at RT. Significant improvement in the electrical properties of the film is achieved using a two-step growth procedure, consists of 300 Å thick interface layer growth at 300°C followed by growth at 400°C. The electron mobility of a 1.8 μm thick two-step grown film at RT is 23 000 cm 2 V −1 s −1. Surface morphology, crystal quality and electrical properties of the grown films are discussed with respect to growth parameters.

Heteroepitaxialgrowth of high quality InSb films on Si(111) substrates using a two-step growth method

We report the molecular beam epitaxial growth of InSbon Si(111) substrates over the temperature range190-400 °C. Epitaxial growth is achieved by suitablyadjusting the growth rate, In/Sb flux ratio and substratetemperature. For growth temperatures up to 300 °C surfacemorphology and epitaxial quality of the film improve withtemperature, whereas above 300 °C, increase in growthtemperature causes deterioration in the epitaxial quality ofthe film. Hall measurements revealed that the electron mobilityof the film increases with growth temperature and for the filmgrown at 300 °C it is about 2200 cm2 V-1 s-1 at room temperature (RT). Significantimprovement in the electrical properties of the film isachieved using a two-step growth procedure, which involves a 300 Åthick interface layer growth at 300 °C followed by growthat 400 °C. Electron mobility of a 1.8 µm thick two-stepgrown film at RT is 23 000 cm2 V-1 s-1 (≈19 000 cm2 V-1 s-1 at 70 K). This is thehighest mobility value we came across for an InSb film grown ona Si(111) substrate without buffer layer. Surface morphology,crystal quality and electrical properties of the grown films arediscussed with respect to growth parameters.

Quality Improvement by Annealing for Flash-evaporated Thin InSb Films

Thin InSb films were prepared at room temperature by a rapid vacuum evaporation (flash evaporation) method using indium antimonide compound as a source material. The characteristics of the films such as microstructure and electrical properties were investigated in terms of heat treatment procedure. The as-deposited InSb films were found to have polycrystalline structure, and their stoichiometry was much better at higher deposition rates. Their characteristics were strongly influenced by successive annealing. The evaporation of Sb from the film caused by annealing led to poor electrical properties of the films. In order to avoid the evaporation of Sb from the film, an attempt was made to cap an as-deposited film with Si02 layer before annealing. The microstructures as well as the galvanomagnetic properties were improved by introducing such capped-annealing. The highest Hall mobility of 2.1 x 10 4 cm 2 /Vs was obtained in an InSb film of 1.0 μm thick, when it was prepared with a deposition rate of 10 nm/s and followed by capped-annealing at 773 K.

Evolution of structural and electronic properties of highly mismatched InSb films

We have investigated the evolution of structural and electronic properties of highly mismatched InSb films, with thicknesses ranging from 0.1 to 1.5 μm. Atomic force microscopy, cross-sectional transmission electron microscopy, and high-resolution x-ray diffraction show that the 0.1 μm films are nearly fully relaxed and consist of partially coalesced islands, which apparently contain threading dislocations at their boundaries. As the film thickness increases beyond 0.2 μm, the island coalescence is complete and the residual strain is reduced. Although the epilayers have relaxed equally in the 〈110〉 in-plane directions, the epilayer rotation about an in-plane axis (epilayer tilt) is not equal in both 〈110〉 in-plane directions. Interestingly, the island-like surface features tend to be preferentially elongated along the axis of epilayer tilt. Furthermore, epilayer tilt which increases the substrate offcut (reverse tilt) is evident in the [110] direction. High-resolution transmission electron microscopy indicates that both pure-edge and 60° misfit dislocations contribute to the relaxation of strain. In addition, as the film thickness increases, the threading dislocation density decreases, while the corresponding room-temperature electron mobility increases. The other structural features, including the residual strain, and the surface and interface roughness, do not appear to impact the electron mobility in these InSb films. Together, these results suggest that free-carrier scattering from the threading dislocations is the primary room-temperature mobility-limiting mechanism in highly mismatched InSb films. Finally, we show quantitatively that free-carrier scattering from the lattice dilation associated with threading dislocations, rather than scattering from a depletion potential surrounding the dislocations, is the dominant factor limiting the electron mobility.

Detection of terahertz radiation from longitudinal optical phonon–plasmon coupling modes in InSb film using an ultrabroadband photoconductive antenna

Terahertz radiation from longitudinal optical (LO) phonon–plasmon coupling modes in InSb films is observed using an ultrafast photoconductive antenna detector. We demonstrate a response frequency of up to 7 THz for a low-temperature-grown GaAs-based photoconductive antenna gated with 25 fs laser pulses. It is found that the emission frequencies of the coupling modes are dependent only on the residual carrier density, not on the excitation carrier density. It is also found that the LO phonon–plasmon oscillations in semiconductors can serve as an efficient THz source.

Optical characterization and transport behaviors of LPMOCVD-grown InSb epitaxial films

InSb films were grown on GaAs substrates by low-pressure metalorganic chemical vapor deposition (LPMOCVD). Far-infrared (FIR) reflectance spectroscopy and Raman scattering has been used to study the lattice vibration behavior of these samples and the effects of III–V source ratios on the films crystalline quality to optimize the growth parameters. Lattice vibration modes were characterized. Film thickness, composition, stoichiometry and depth profiles were studied. The carrier concentration, mobility, effective mass as well as the dielectric behavior of these films are fitted by a model of dielectric response.

Effect of current flow direction on the heteroepitaxial growth of InSb films on Ge/Si(001) substrate heated by direct current

Germanium is a suitable material as the buffer layer for the heteroepitaxial growth of InSb films on a Si(001) substrate. It reduces the large lattice mismatch of about 19.3% between Si and InSb to about 14.5%. InSb films grown on the islanded Ge buffer layers on a Si(001) substrate at elevated temperature are strongly oriented in 〈001〉 direction. The bias for heating the substrate was changed in both directions; usual and reverse. Two-step growth procedure is effective to improve the crystal quality and the surface morphology of the InSb films. However, the surface morphology of the films was divided into two regions; the first region is smooth, whereas the second region consists of the colligated crystals. The smooth surface appears near the positive electrode in the usual bias condition. On the contrary, in the reverse bias condition, the smooth surface appears near the reverse electrode. The similar results were obtained for the growth of InSb on Ge(001) substrate. These results may not be due to the thermal gradient of the substrate.

Growth temperature effect on the heteroepitaxy of InSb on Si(111)

Direct growth of InSb on Si(111) substrate is achieved by suitably adjusting the growth rate and substrate temperature. In this report, we detail the role of stoichiometry and growth temperature in the evolution of reflection high-energy electron diffraction (RHEED) patterns, surface morphology and the crystal quality. InSb is grown on Si(111)-(7×7) surface by evaporating In and Sb simultaneously. Results indicate that smooth heteroepitaxial InSb films could be grown up to 300°C, and above this temperature, severe degradation in the epitaxial quality of the films is observed. Properties of the Sb-rich films are compared with those of In-rich films and the importance of stoichiometry in the crystal quality is discussed.

Development of High-Efficiency Strip-Coupled Surface Acoustic Wave Convolver Using GaSb/InSb/AlGaAsSb/LiNbO3 Structures

We have fabricated a strip-coupled surface acoustic wave [SAW] convolver using GaSb/InSb/AlGaAsSb heterostructures grown on a LiNbO3 substrate. An InSb thin film with an AlGaAsSb buffer layer was grown on a 128° Y-X LiNbO3 substrate by molecular beam epitaxy; a very high electron mobility of 7000 cm2/(V·s) in 200-nm-thick InSb films was achieved. We have fabricated a strip-coupled SAW convolver as a new device and have achieved a very high output efficiency (F value) of -14 dBm for modified semiconductor and electrode structures.

Doping of InSb thin films with lead

The incorporation of lead into polycrystalline InSb thin films is investigated. Several experimental methods are used to determine the distribution and solubility limit of lead in the InSb films. Considering the electrical neutrality of Pb in InSb films and difficulties in distinguishing between the lead incorporated into the lattice and lead in the metallic inclusions, the solubility of Pb in InSb is not determined in detail. The results show that the solubility should be well below 0.2at.%, which is considerably smaller than that of about 0.5at.% found in the earlier investigations. This behaviour of Pb is explained on the assumption that it substitutes in Pb–Pb pairs for the nearest-neighbour In–Sb pairs. The only clear manifestation of the presence of Pb in the InSb lattice is the weak localisation effect at temperatures below 7K. The magnitude of the effect and the temperature range of its observation are appreciably higher than those found previously in InSb.

Two-dimensional growth of InSb thin films on GaAs(111)A substrates

Heteroepitaxy of high-quality InSb films was performed directly on GaAs surfaces by using molecular beam epitaxy. Despite the 14.6% lattice mismatch, two-dimensionally grown InSb on GaAs(111)A substrates were obtained from the initial stage, but not on (001) substrates. A conductive layer was formed from the early stage of the growth on the (111)A surface, and the mobilities and carrier concentrations of InSb on (111)A substrates suggested a low defect density due to confinement of the dislocations to the interface.

Morphological Evolution in Highly Strained InSb/InAs(001)

ABSTRACTWe investigated the morphological evolution of InSb grown on InAs (001) substrates (lattice mismatch = 6.9%) as a function of film thickness. Due to the very large lattice mismatch, growth proceeded via the Volmer-Weber mode. The morphological evolution of highly strained InSb films proceeds through several regimes as a function of thickness. The films initially nucleate isolated 3D islands even in the earliest stages of growth. The islands then coarsen and coalesce at slightly higher thicknesses, with some evidence of cooperative nucleation, or the sequential nucleation of islands and pits. Once the islands coalesce, the morphology evolves into long ridges aligned along the [110], however, those films are still discontinuous. At a thickness =100nm, the films finally become completely continuous and 2D growth proceeds via step flow of growth spirals present on the surface.