InAs Thin Films Research Articles

Large-area epitaxial growth of InAs nanowires and thin films on hexagonal boron nitride by metal organic chemical vapor deposition

Large-area epitaxial growth of III–V nanowires and thin films on van der Waals substrates is key to developing flexible optoelectronic devices. In our study, large-area InAs nanowires and planar structures are grown on hexagonal boron nitride templates using metal organic chemical vapor deposition method without any catalyst or pre-treatments. The effect of basic growth parameters on nanowire yield and thin film morphology is investigated. Under optimised growth conditions, a high nanowire density of 2.1 109 cm−2 is achieved. A novel growth strategy to achieve uniform InAs thin film on h-BN/SiO2/Si substrate is introduced. The approach involves controlling the growth process to suppress the nucleation and growth of InAs nanowires, while promoting the radial growth of nano-islands formed on the h-BN surface. A uniform polycrystalline InAs thin film is thus obtained over a large area with a dominant zinc-blende phase. The film exhibits near-band-edge emission at room temperature and a relatively high Hall mobility of 399 cm−2/(Vs). This work suggests a promising path for the direct growth of large-area, low-temperature III–V thin films on van der Waals substrates.

Gate-controlled proximity magnetoresistance in In1−xGaxAs/(Ga,Fe)Sb bilayer heterostructures

The magnetic proximity effect (MPE), ferromagnetic coupling at the interface of magnetically dissimilar layers, attracts much attention as a promising pathway for introducing ferromagnetism into a high-mobility non-magnetic conducting channel. Recently, our group found giant proximity magnetoresistance (PMR), which is caused by MPE at an interface between a non-magnetic semiconductor InAs quantum well (QW) layer and a ferromagnetic semiconductor (Ga,Fe)Sb layer. The MPE in the non-magnetic semiconductor can be modulated by applying a gate voltage and controlling the penetration of the electron wavefunction in the InAs QW into the neighboring insulating ferromagnetic (Ga,Fe)Sb layer. However, optimal conditions to obtain strong MPE at the InAs/(Ga,Fe)Sb interface have not been clarified. In this paper, we systematically investigate the PMR properties of In1-xGaxAs (x = 0%, 5%, 7.5%, and 10%) / (Ga,Fe)Sb bilayer semiconductor heterostructures under a wide range of gate voltage. The inclusion of Ga alters the electronic structures of the InAs thin film, in particular changing the effective mass and the QW potential of electron carriers. Our experimental results and theoretical analysis of the PMR in these In1-xGaxAs/(Ga,Fe)Sb heterostructures show that the MPE depends not only on the degree of penetration of the electron wavefunction into (Ga,Fe)Sb but also on the electron density. These findings help us to unveil the microscopic mechanism of MPE in semiconductor-based non-magnetic/ferromagnetic heterojunctions.

Structural and Electronic Properties of Polycrystalline InAs Thin Films Deposited on Silicon Dioxide and Glass at Temperatures below 500 °C

Polycrystalline indium arsenide (poly InAs) thin films grown at 475 °C by metal organic vapor phase epitaxy (MOVPE) are explored as possible candidates for low-temperature-grown semiconducting materials. Structural and transport properties of the films are reported, with electron mobilities of ~100 cm2/V·s achieved at room temperature, and values reaching 155 cm2/V·s for a heterostructure including the polycrystalline InAs film. Test structures fabricated with an aluminum oxide (Al2O3) top-gate dielectric show that transistor-type behavior is possible when poly InAs films are implemented as the channel material, with maximum ION/IOFF > 250 achieved at −50 °C and ION/IOFF = 90 at room temperature. Factors limiting the ION/IOFF ratio are investigated and recommendations are made for future implementation of this material.

Nonuniform Carrier Heating Induced Nonlinear Electron Transport Properties in Asymmetrically Necked InAs Mesa Structures

IntroductionTerahertz (THz) wave has been very attractive light for scientific and practical applications such as light source for characterizing fundamental physics on ultra-fast carrier dynamics in semiconductors and imaging applications in the submillimeter wavelength regime. Therefore, there have been studied on various kind of emitting and detecting methods on THz waves in this quarter century. So far, we also have proposed simple and low-cost THz wave source with InAs thin films grown on GaAs substrates combining with a time-domain spectroscopy system [1, 2]. In case of THz detectors, there are not so many techniques which enable to detect THz wave at room temperature with high responsivity without biasing. For example, square-law field rectifier detectors, such as Schottky diodes and InGaAs-based bow-tie diodes, respond to THz electric field at room temperature with no external power supply [3]. Nonlinear current-voltage characteristics of the latter technique is based on unique operation principle which is generated by nonuniform carrier heating in asymmetric bow-tie shaped planar structures. Since InAs possesses one of the highest electron mobility at room temperature among semiconductors, this material based thin films will be hopeful candidate for detecting THz waves by fabricating this unique nonlinear device structures on them. In this paper, we devise utilizing InAs THz wave emitter thin films to base material for asymmetrically necked bow-tie mesa structures for the THz detector. As a first step of this idea, nonlinear current-voltage characteristics of these devices are presented. We especially discuss on the curvature of current-voltage characteristic at zero-bias point which is closely related to the sensitivity on square-law detection for THz wave.ExperimentalNominally undoped InAs thin films were epitaxially grown on semi-insulating GaAs (100) substrate by molecular beam epitaxy. For improving the crystal quality of InAs channel layer, 150 nm thick InAs buffer layer was directly grown with gradually changing growth temperature from 300 to 500°C on GaAs substrate. An 1 µm think InAs channel layer was grown on this buffer layer at 450°C. This growth condition is same as that of THz emitter InAs films we have reported [2]. The patterning of asymmetric bow-tie mesa structure was carried out by photo lithography and phosphoric acid based wet chemical etching. After defining mesa structures, in order to investigate the film thickness dependence on nonlinear current properties, some samples were performed recess etching for InAs channel, which were made each thickness to be 265 nm, 435 nm, 625 nm and 835 nm. Finally, non-alloyed ohmic contact metals of Ti/Pt/Au (50/30/170 nm) were deposited by electron-beam evaporation technique and defined by lift-off. The structure of asymmetric bow-tie diode and the measurement configuration are shown in Fig. 1. Current-voltage characteristics were measured by using Keithley 4200A-SCS system at room temperature.Results and Conclusion Typical current-voltage characteristic of the investigated InAs asymmetric bow-tie diode is represented in Fig. 2, which was the result measured with the sample of 265 nm thick InAs channel. It showed clear asymmetric current-voltage characteristic depended on the polarity of applied voltage, which was considered originated from nonlinear carrier transport related to non-uniform carrier heating in asymmetric mesa structure. In order to evaluate the nonlinearity of current-voltage curve at zero-biased point, the zero-biased curvature coefficient γ was calculated, which is given by the formula written in Fig. 3. A fifth order polynomial fit was utilized to current-voltage curves in determining the curvature. As shown in Fig. 3, the zero-bias curvature clearly depended on thickness of InAs thin film. The highest zero-bias curvature of 0.12 V-1 was obtained in the thinnest sample. In addition, this value was about 2.2 times larger than that of the GaAs/AlGaAs heterostructure-based asymmetric bow-tie diode which had the same shape and size (not shown here). These results indicate that the InAs thin film for THz radiation has possibility to be applied to square-law detection device for THz wave. The details of nonlinearity which depends on mesa shape and size and comparison between InAs based structures and that of GaAs/AlGaAs will be discussed at the conference.

Nonmetallic Broadband Visible-Light Absorbers With Polarization and Incident Angle Insensitivity

We have proposed and theoretically analyzed nonmetallic broadband visible-light absorbers based on alternating SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /InAs thin films on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> substrate. Compared with the conventional absorbers, the proposed SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /InAs structure can achieve excellent absorption within a smaller volume. The average absorption can exceed 97% in the wavelength range of 300-850 nm. With a two-dimensional InAs grating atop, the device can achieve the average absorption of >92% with insensitivity to light polarization and incident angles. Due to the advantages of broadband and near-unity absorption, polarization and incident angle insensitivity, controllable and mature fabrication processes, the proposed visible-light absorbers will find wide applications in solar energy harvesting, thermal emission, and water splitting.

InAs nano-ridges and thin films grown on (001) silicon substrates

Monolithic integration of InAs related devices on (001) Si platforms offers potential to extend integrated Si photonics to the mid-infrared (MIR). Here, we systematically studied the hetero-epitaxial growth of in-plane InAs nano-ridges and coalesced thin films on CMOS-standard (001) Si wafers. We started with the growth and optimization of in-plane InAs nano-ridges inside nano-scale Si trenches and developed a three-step growth procedure with a reduced growth rate to obtain uniform InAs nano-ridges with excellent crystalline qualities. We then developed a coalescence process for the optimized InAs nano-ridges to evolve into high quality continuous thin films. In the parametric growth study, we found that a low coalescence rate results in the formation of large InAs islands, while a high coalescence rate promotes the creation of uniform InAs thin films. These InAs/Si templates could serve as virtual substrates for the growth of light emitters and detectors in MIR Si photonics.

Scaling study of molecular beam epitaxy grown InAs/Al2O3 films using atomic force microscopy

Scaling study of polycrystalline InAs thin films grown by molecular beam epitaxy on c-plane sapphire (001) substrate has been presented using atomic force microscopy, corresponding height-height correlation function and two-dimensional fast Fourier transform profiles. Height-height correlation function profiles exhibit oscillations at larger lateral distances along with ring-like features in the respective two-dimensional fast Fourier transform scans and clearly indicate mound-like surface morphology. Scaling parameters, interface width and lateral correlation length were extracted and their dependence on the growth temperatures were investigated. The growth mechanism has been well explained in terms of diffusion effects and the obtained parameters qualitatively agrees with the parameters obtained for the growth of InAs films grown on Si(100) substrate under identical growth conditions. Our study suggests that molecular beam epitaxy grown InAs thin films on lattice mismatched substrates (c-plane sapphire(001) and Si(100) substrate) follows the same growth behavior under identical growth conditions.

Transport Properties in InAs Thin Films with Different Degrees of Disorder Near the Metal–Insulator Transition

Transport properties of Indium Arsenide (InAs) films deposited at different working pressures are investigated in the temperature interval of T ∼ 2–250 K. Electrical transport of InAs films is related to the degree of disorder, which increases as working pressure increases. Activated conductivity models satisfactorily describe conduction in the localized band-tails at high temperatures, while conductivity shows metallic characteristic at low temperatures for μc-InAs samples. The critical conductivity exponent of μc-InAs is close to 1, which indicates that μc-InAs samples exhibit a close proximity to the metal–insulator transition. The product of aB and n1/3 for samples S1 and S2 is 0.236 and 0.207, respectively, which is roughly consistent with the Mott criterion. But for α-InAs samples in the high temperature region, electron transport is described by conduction in extended states and in localized states near the Fermi level. Furthermore, a crossover from Mott variable range hopping (VRH) to the Efros–Shklovskii VRH mechanism is observed in α-InAs thin films at low temperatures.

The hopping variable range conduction in amorphous InAs thin films

This paper studies the influence of temperature on electrical resistivity in α-InAs thin films between 30 K-2K based on the analysis of Mott VRH model and ES VRH model. The effect of the interactions between electrons at lower temperature must be considered, therefore, ES VRH conduction will dominate mechanism, and the crossover from Mott to ES VRH conduction is observed about 7 K. Based on available experiment data and VRH conduction model, the parameters of VRH conduction are determined. And the calculated values of TC are consistent with the experimental results. In addition, RM/ξ, ΔM/kT, RES/ξ and ΔES/kT are satisfied with the validity of Mott and ES models. Furthermore, the temperature dependence of resistivity at low temperature obeys a universal scaling law, which well describes the overall temperature range of VRH conduction. However, the values of T’M from the universal function are two order of magnitudes lower than TM deduced from fitting experiment.

Qualitative analysis of growth mechanism of polycrystalline InAs thin films grown by molecular beam epitaxy

The mechanism of surfaces/interfaces and precise control of growth morphology is a key parameter for any specific device application. Herein, we report on a qualitative growth study of molecular beam epitaxy-grown polycrystalline InAs thin films on a lattice-mismatched Si(1 0 0) substrate using atomic force microscopy. The height-height correlation function (HHCF) and power spectral density function (PSDF) were employed to analyze the surface structures. Clear oscillatory behavior in the HHCF for sufficiently larger lateral distances suggests a mound-like morphology, which was confirmed by the existence of a characteristic frequency peak in the PSDF. The growth mechanism is described qualitatively by the Schwoebel barrier (roughening) effect coupled with the Mullins diffusion model (smoothing effect).

Low temperature growth and physical properties of InAs thin films grown on Si, GaAs and In0.53Ga0.47As template

Integration of III-V semiconductors on a Si platform is interesting for both nanoelectronic and optoelectronic devices. Among the different challenges, the formation of low resistive contacts remains essential. In this paper, the growth by metalorganic chemical vapor deposition of thin InAs film as intermediate layer between the III-V materials and the metal has been studied on different templates: Si(100), GaAs/Si(100) and In0.53Ga0.47As/InP/GaAs/Si(100). We have shown that the formation of a continuous layer with low surface roughness is obtained at a growth temperature below 500°C with a two steps growth mode. The influence of the substrate on which the InAs is deposited, is investigated through morphological and structural properties. We observed an evolution of the InAs surface morphology versus the templates used. The surface roughness value obtained is 2.5nm, 0.9nm and 2nm respectively for a 30nm InAs layer grown on Si(100), GaAs/Si(100) and In0.53Ga0.47As/InP/GaAs/Si(100). Structural characterization shows that InAs crystal quality is better when GaAs/Si(100) are used as templates compared to growth on Si(100) and In0.53Ga0.47As/InP/GaAs/Si(100). The n-type doping using silicon as impurity allows a doping level of 5×1019cm−3 for all InAs layers, which favors the formation of low resistance contacts. Moreover we measured aa minimum resistivity of 6×10−4Ω·cm−1 for InAs on Si(100) and 10−4Ω·cm−1 for InAs on GaAs/Si(100) and In0.53Ga0.47As/InP/GaAs/Si(100).

Study for Enhancement of Terahertz Radiation Using GaSb/InAs Heterostructures

GaSb/InAs heterostructures were investigated for the enhancement of terahertz (THz) radiation from an InAs thin film excited by a femtosecond laser. Taking advantage of the large conduction band discontinuity between GaSb and InAs, electrons excited in the GaSb layer gain a large excess energy when injected into the InAs radiation layer. Enhancement of the THz radiation by a factor of approximately two was observed when the surface pinning position was controlled to reduce the surface electric field by the introduction of a thin InAs cap layer.

High accuracy magnetic field sensors with wide operation temperature range

n+InAs(Si) epitaxial thin films heavily doped by silicon and Hall effect magnetic field sensors based on this structures have been fabricated and studied. We have demonstrated the successful formation of highly doped InAs thin films (∼100 nm) with the different intermediate layer arrangement and appropriate electron mobility values. Hall sensors performance parameters have been measured in wide temperature range. Obtained sensitivity varied from 1 to 40 Ω/T, while the best linearity and lower temperature coefficient have been found in the higher doped samples with lower electron mobility. We attribute this to the electron system degeneracy and decreased phonon contribution to electron mobility and resistance.

Non-destructive carrier concentration determination in InAs thin films for THz radiation generating devices using fast differential reflectance spectroscopy

We present a fast and robust optical method of determining carrier concentrations in heavily doped layered structures. We discuss several advantages of the technique as compared to other, more commonly applied methods using as an example InAs based devices used for THz radiation generation. Our approach leads to a more accurate estimation of doping levels in the investigated structures and aids the standard Hall measurements in precise predictions of radiative efficacy in the THz region. Predicted enhancement factors reproduce THz-Time Domain Spectroscopy (TDS) experiment results within a 2 % accuracy.

Preparing and characterization of indium arsenide (InAs) thin films by chemical spray pyrolysis (CSP) technique

In this research, InAs thin films were prepared by chemical spray pyrolysis method at different substrate temperatures (250°C, 280°C, 310°C), with fixing the molarity of solution to 0.035M and the deposition time to 30min. X-ray diffraction shows that the structure of InAs films were polycrystalline and the most intensity planes approximately 25°.2′ and 29°.1′ corresponding to (111) and (200) orientation respectively. Surface analysis by atomic force microscopy (AFM) showed that the morphology of the deposited films is nanostructured. Optical measurements were characterized by UV–vis spectroscopy showed that the transmittance and the energy gap of InAs films decreased with increasing the substrate temperature due to the decreasing in the density of state by quantum confinement. Electrical characteristics showed that InAs film has been a negative Hall coefficient (RH) value which confirm that InAs is n-type semiconductor and has carrier’s concentration about 1.67×1011cm−3.

A single-source precursor approach to solution processed indium arsenide thin films.

This paper reports the synthesis of the novel single-source precursor, [{(MeInAs t Bu)3}2(Me2InAs( t Bu)H)2] and the subsequent first report of aerosol-assisted chemical vapour deposition of InAs thin films. Owing to the use of the single-source precursor, highly crystalline and stoichiometric films were grown at a relatively low deposition temperature of 450 °C. Core level XPS depth profiling studies showed some partial oxidation of the film surface, however this was self-limiting and disappeared on etch profiles. Valence band XPS analysis matched well with the simulated density of state spectrum. Hall effect measurements performed on the films showed that the films were n-type with promising resistivity (3.6 × 10-3 Ω cm) and carrier mobility (410 cm2 V-1 s-1) values despite growth on amorphous glass substrates.

Reflection Layer Mediated Enhancement of Terahertz Radiation Utilizing Heavily-Doped InAs Thin Films

We present the result of incorporating a heavily Si-doped InAs reflection layer into a terahertz emitting, InAs thin film based, structure. We demonstrate the increase of the radiated electric field intensity relative to a typical, n-type InAs bulk reference crystal using terahertz time domain spectroscopy (THz-TDS). With our approach more than a 2 fold increase in the electric field can be obtained. We compare our experimental findings with values obtained from calculations in the Drude model to obtain good agreement.

Direct growth of a 40 nm InAs thin film on a GaAs/Ge heterostructure by metalorganic chemical vapor deposition

In this paper, the authors directly grew an InAs thin film (40 nm) by metalorganic chemical vapor deposition on GaAs/Ge substrates by using flow-rate modulation epitaxy with an appropriate V/III ratio. The growth of a high-quality InAs thin film with periodic 90° misfit dislocations was related to a uniform monolayer In atom distribution at the InAs/GaAs interface. The In monolayer effectively minimized the difference between surface energy and strain energy, producing a stable interface during material growth. The authors also found that a tightly controlled V/III ratio can improve the quality of the InAs islands on the GaAs/Ge heterostructures, though it is not the key factor in InAs thin-film growth.

Electrochemically Gated Alloy Formation of Crystalline InAs Thin Films at Room Temperature in Aqueous Electrolytes

Crystalline InAs films have been prepared directly at room temperature through a new electrochemically induced alloying method by controllably reducing As2O3 dissolved in an alkaline aqueous solution at an indium (In) foil electrode. Steady-state Raman spectra, transmission electron microscopy, and selected area electron diffraction indicated that the as-prepared films crystallize in the zincblende phase with no further thermal treatments. Cyclic voltammetry measurements, optical images, and steady-state Raman spectra confirmed that a clean oxide-free interface is critical for the successful formation of the binary InAs phase. The salient feature of this work is the use of simple aqueous electrochemistry to simultaneously remove passive metal oxides from the In(s) metal surface while controllably reducing dissolved arsenic oxide at the interface to drive the In–As alloying reaction. Raman spectral mapping data illustrate that the resulting film coverage and homogeneity are a strong function of the formal ...

Growth Parameters for Thin Film InBi Grown by Molecular Beam Epitaxy

The alloying of bismuth with III–V semiconductors, in particular GaAs and InAs thin films grown by molecular beam epitaxy (MBE), has attracted considerable interest due to the accompanying changes in band structure and lattice constant. Specifically, bismuth incorporation in these compounds results in both a reduction in band gap (through shifting of the valence band) and an increase in the lattice constant of the alloy. To fully understand the composition of these alloys, a better understanding of the binary endpoints is needed. At present, a limited amount of literature exists on the III-Bi family of materials, most of which is theoretical work based on density functional theory calculations. The only III-Bi material known to exist (in bulk crystal form) is InBi, but its electrical properties have not been sufficiently studied and, to date, the material has not been fabricated as a thin film. We have successfully deposited crystalline InBi on (100) GaAs substrates using MBE. Wetting of the substrate is poor, and regions of varying composition exist across the substrate. To obtain InBi, the growth temperature had to be below 100 °C. It was found that film crystallinity improved with reduced Bi flux, into an In-rich regime. Additionally, attempts were made to grow AlBi and GaBi.