Thin InAs Layer Research Articles

X-Ray Interface Characterization of Buried InAs Layers on GaAs (001)

Ultra thin buried InAs layers on GaAs (001) crystals prepared by molecular beam epitaxy are structurally characterized using synchrotron radiation. Grazing incidence X-ray reflectivity and crystal truncation rods were utilized to determine the average layer thickness, interface roughness, and the stoichiometry of the layers. From X-ray standing wave experiments the In lattice site and vertical distribution are determined. We discuss our results in view of the structural transition of the layer system with In deposition from 1.0 to 2.1 ML.

Optical properties of near surface-InAs quantum dots and their formation processes

The morphological evolution of thin layers of InAs deposited on (0 0 1)GaAs has been investigated by photoluminescence (PL) and atomic force microscopy (AFM). We observe PL features that correspond to the transformation of the InAs wetting layer and 2D islands into quantum dots (QDs), which is supported by the AFM study. Variation in the PL spectra is also observed as a function of the thickness of the GaAs layer deposited on top of the InAs layer. Luminescence intensity from both the QDs and the wetting layer (WL) picks up at a thickness of about 10–20 monolayers. As the thickness is increased, uprise in PL intensity for both QDs and WL together with a narrowing in the WL peak is observed.

Kink-free characteristics of AlSb/InAs high electron mobility transistors with planar Si doping beneath the channel

AlSb/InAs n-channel inverted-structure high electron mobility transistors (i-HEMT's) are realized by incorporating a Si doping sheet into a thin InAs layer that is embedded within the lower AlSb barrier. i-HEMT's with a 1 /spl mu/m /spl times/25 /spl mu/m gate size exhibit kink-free operation at room temperature with high drain current, high extrinsic transconductance, and low gate leakage. Results indicate potential for use in high-speed applications.

AlSb/InAs HEMTs using modulation InAs(Si)-doping

AlSb/InAs HEMTs have been fabricated using Si-doping in a very thin (9 A) InAs layer located in the upper AlSb barrier. Quantum Hall measurements show that there is no parallel channel. Devices with a 0.5 µm gate length exhibit a drain current density of > 1 A/mm and an fTLg product of 30 GHzµm at VDS = 0.4 V after correction for the gate bonding pad capacitance.

Fabrication of p+-gate InAs-channel HEMT based on InP

We have successfully fabricated a p +-gate InGaAs/InAlAs HEMT with a thin InAs layer inserted in the InGaAs channel. An intrinsic transconductance of over 400 mS mm −1 and maximum drain current of 250 mA mm −1 were obtained in a 1 μm gate length device with relatively thick gate-to-channel barrier of 375Å. We have confirmed that the p +-gate InAs-channel HEMT operates as well as conventional Schottky gate HEMT.

InAs on InP: Intermediate alloy formation and interface vibrations

We present a detailed investigation of the vibrational modes of single thin InAs layers directly grown on InP substrate. The Raman spectra have revealed the presence of features besides the longitudinal-optical and transverse-optical modes related to InP and InAs. We have succeeded in distinctly detecting Raman modes due to the presence of an intermixed ${\mathrm{In}}_{x}{\mathrm{As}}_{1\ensuremath{-}x}\mathrm{P}$ layer resulting from an incorporation of arsenic in the InP substrate. Moreover, our Raman data show unusual intense features related to the lattice vibrations of interface bonds. The observed energies of these interface modes are in good agreement with the calculation based on a modulated dielectric model. This work clearly demonstrates that the vibrational properties of heterostructures can be sensitive to the structure of the interface and that Raman spectroscopy is a powerful tool to investigate the crystal structure of heterostructures as well as the interfacial chemistry.

High-performance double-modulation-doped InAlAs/InGaAs/InAs HFETs

We demonstrate the improvement of double-sided-doped InAlAs/InGaAs MODFETs by inserting a thin InAs layer in the center of the conventional InGaAs channel. A maximum extrinsic transconductance of 1.4 S/mm is achieved for 0.13-/spl mu/m devices. The current gain cutoff frequency of this device is as high as 265 GHz. Delay time analysis shows a significant improvement in the effective saturated velocity, from 2.4/spl times/10/sup 7/ cm/s for LM devices to 3.1/spl times/10/sup 7/ cm/s for InAs devices. We believe the superior performance of this device is primarily due to the reduction of scattering from donor layers, especially under the channel, and the interface roughness, which is achieved by inserting a 4-nm InAs layer in the channel.

Selective area etching of III–V semiconductors using TDMAAs and TDMASb in metalorganic molecular beam epitaxy chamber

Abstract Selective area etching of SiO 2 -masked GaAs using trisdimethylaminoarsenic (TDMAAs) is studied. GaAs substrates are partly masked with stripe shaped SiO 2 films along the [0 1 1] and [0 1 1] directions. Cross-sectional scanning electron microscopy observation shows that the etched shape depends on both the direction of the mask and substrate temperature, and is almost independent of the TDMAAs flow rate. At low substrate temperatures, the (1 1 1)B surface is preferentially formed and a V-shaped groove is formed for the [0 1 1] mask direction. With increasing substrate temperature, the V-groove changes to the channel with vertical side walls due to the drastic increase of the etching rate of (1 1 1)B. For the [0 1 1] mask direction, the vertical (0 1 1) plane is formed at all temperatures. It is found that etched shapes are determined by the difference of etching rates and that etching rates are influenced by the crystal structure on the surface. On the other hand, the etching rate of GaSb by TDMASb is independent of substrate surface orientation. This is because the bond strength of GaSb is weak and the etching proceeds along the direction of molecular beams. Enhanced etching rate is observed for InP by TDMAAs, which is explained by the formation of thin InAs layer on InP due to the irradiation of As released from TDMAAs.

Fabrication of p+-Gate InAs-Channel HEMT Based on InP

We have successfully fabricated a p+- n junction gate InGaAs/InAlAs high electron mobility transistor (HEMT) with a thin InAs layer inserted in the InGaAs channel. An intrinsic transconductance of over 400 mS/mm and maximum drain current of 250 mA/mm were obtained in a 1 µ m gate length device with relatively thick gate-to-channel barrier of 375 Å. We have also applied the present fabrication method to 0.25 µ m gate length device using electron beam lithography and wet chemical etching, verifying the decent dc operation with reduced gate leakage current. T-shaped gate electrode was shown to be successfully fabricated for the basic investigation of HEMT for high frequency operation.

Substitution of InP layers to InAs for strain compensation in [formula omitted] superlattices

In this study controlled substitution of P by As atoms, by exposing an InP surface to cracked arsine, is demonstrated to form thin InAs layers. All structures have been grown by chemical beam epitaxy. The effect of the exposure time has been investigated in InAs single and multiple quantum wells. Characterisation was performed by X-ray diffraction and photoluminescence spectroscopy. A two-stage substitution process is concluded. During the fast first stage the top P layer is exchanged by As. Longer exposure times lead to the complete substitution of the P layer underneath. In the mean time a three-dimensional rearrangement results in the formation of InAs islands. These thin compressed InAs layers have successfully been used for strain compensation in Ga x In 1 − x As InP superlattice structures.

Self-aggregation of quantum dots for very thin InAs layers grown on GaAs.

Low-temperature photoluminescence and transmission electron microscopy of InAs/GaAs quantum wells grown by molecular-beam epitaxy show that InAs self-aggregation of InAs quantum dots is a continuous phenomenon and that quantum dots nucleate at the well interfaces for nominal InAs layer thicknesses much smaller than commonly reported in the literature (i.e., 1.6\ifmmode\pm\else\textpm\fi{}0.1 ML). A good agreement is also found between the self-aggregated dot sizes estimated from the photoluminescence emission energies and those directly obtained from transmission electron microscopy measurements.

Phonons in single thin epitaxial layers of InAs on InP

We have used Raman spectroscopy to investigate the vibrational properties of a series of single thin layers of InAs grown on (100) InP substrate by molecular beam epitaxy with a layer thikness between 3 and 9 monolayers. Sensitivity to thin layers, down to 3 monolayers, has been successfully achieved by using incident photon energy resonant with the E 1 gap of InAs. In addition to the LO and TO modes related to InP and InAs we have observed new structures assigned to the presence of an intermixed InAs xP 1−x alloy at the interface region, and unusually intense features just below bulk optical phonon energies related to the lattice vibrations of interface bonds. We have attributed these modes to interface phonons and analyzed their frequencies by using a modulated dielectric model. This study demonstrates that Raman scattering is not only sensitive to a thin layer at the surface, but provides detailed quantitative information on the vibrational structure of complex stackings which takes place during the first stage of heteroepitaxy of semiconductors.

Epitaxial lift-off of thin InAs layers

We describe the use of the epitaxial lift-off technique to remove thin layers of InAs from the GaAs substrates on which they were grown and subsequently bonded to glass and silicon substrates. Lift-off was accomplished by taking advantage of the high etching selectivity between AlSb and InAs in an aqueous hydrofluoric acid etching solution, allowing a thin layer of AlSb to serve a sacrificial layer to facilitate the lift-off of the InAs. The InAs layers were transferred with little measurable effect on the electrical and structural properties of the films, as evidenced by Hall effect and x-ray measurements. The technique can easily be extended to transfer more-complex GaSb/AlSb/InAs structures.

Role of the substrate deoxidation process in the growth of strained InAs/InP heterostructures

We have investigated the role of the arsenic flux used during the substrate deoxidation process in the MBE (molecular beam epitaxy) growth of strained InAs/InP heterostructures. Two different experiments were performed: (i) thermal cleaning of the InP wafer under an As flux at different exposure times and (ii) the growth of very thin InAs layers (3–9 ML). The samples grown were characterized by Raman spectroscopy and selected area X-ray photoelectron spectroscopy. The results obtained demonstrated the formation of an InAs x P 1− x sublayer at the interface of the InAs/InP system. The annealing of InP under an As flux promotes not only As → P substitution on the surface, but also the subsequent diffusion of As atoms into the deeper subsurface region of InP.

Improving the characteristics of an [formula omitted] inverted HEMT by inserting an InAs layer into the InGaAs channel

A novel InAlAs InGaAs inverted HEMT with a thin InAs layer inserted into the InGaAs channel (InAs-inserted-channel i-HEMT) is proposed and its electron transport properties and device performances are investigated. By optimizing the thickness of the InAs layer and its distance from the underlying InAlAs spacer layer, a maximum mobility of 13,600 cm 2/Vs at 300 K and 63,500 cm 2/Vs at 77 K were attained. The inverted HEMT structure resulted in an extremely high voltage gain, over 60 in a 0.7 μm gate-length device, and a gate-to-drain breakdown voltage as high as 9 V. This voltage gain resulted in a maximum oscillation frequency for a 0.7 μm gate-length device of 81 GHz, 14% higher than that of an InAs-inserted-channel normal HEMT.

InAlAs/InP heterostructures: Influence of a thin InAs layer at the interface

InAlAs lattice matched on InP heterostructures with a thin InAs layer of variable thickness intentionally added at the interface has been grown by molecular-beam epitaxy and characterized by photoluminescence. Radiative transitions, the position of which is correlated with the InAs thickness, are systematically observed, even in samples without any added InAs layer. This shows that, even in the latter case, type-I transitions are observed at the interface. Following this result, it is proposed that a transition around 1.2 eV, previously assigned to type-II transitions, results in fact from type-I recombinations in a quantum well at the interface. The spatially indirect type-II transitions would occur at ≊1.3 eV, and could be observed up to now only for reverse interfaces (InP grown on InAlAs).

Dynamics of island formation in the growth of InAs/InP quantum wells

A thin InAs layer grown in a quasi-two-dimensional film over InP reorganizes into islands if left to anneal under arsine. This surface transformation is inhibited at lower arsine fluxes. With increasing temperature, the surface transformation is activated as long as the effective arsine coverage is sufficient.

Magnetotransport in lateral periodic potentials formed by surface-layer-induced modulation in InAs-AlSb quantum wells

We report the realization of strong lateral superlattice potentials in not-intentionally doped InAs-AlSb quantum wells. By spatially alternating the surface layer between thin layers of InAs and GaSb, which shift the pinning position of the Fermi level at the surface, we induce a lateral density modulation of 4×1011 cm−2, equivalent to a potential modulation of 30 meV inside quantum wells 20 nm away from the surface. Both one- and two-dimensional lateral potentials were fabricated and studied by magnetotransport measurements. Strong commensurability oscillations are observed.

Electron beam-enhanced etching of InAs in Cl2 gas and novel in situ patterning of GaAs with an InAs mask layer

We propose and demonstrate a novel in situ patterning process of GaAs and GaAs/AlGaAs heterostructures in which a thin InAs layer is used as an electron-beam resist layer for Cl2 gas etching in ultrahigh vacuum environment. It has been found that the etch rate of InAs by Cl2 gas is far lower (by a factor of 500) than that of GaAs but this etch rate can be enhanced by electron beam irradiation by a factor of 20, allowing the pattern formation in the InAs mask layer. By delineating a stripe pattern in the InAs resist and subsequently etching in situ the GaAs underneath, we have successfully formed a fine V groove. Since this process is clean and damage free, it is suited for the fabrication of quantum structures in which high-quality etch/regrowth interfaces are required.

Narrow-gap semiconductor magnetic-field sensors and applications

Narrow-gap semiconductors have been used for decades in the fabrication of magnetic field sensors, such as magnetoresistors and Hall sensors. Magnetic field sensors are, in turn, used in conjunction with permanent magnets to make contactless potentiometers and rotary encoders. This sensing technology offers the most reliable way to convert a mechanical movement into an electrical signal, and is widespread in automotive applications. Recent developments in the growth of thin epitaxial layers of InAs and InSb on semiinsulating GaAs or InP substrates have resulted in the development of magnetoresistors with excellent sensitivity and operating temperatures up to 285 degrees C. Magnetoresistors and Hall sensors require a very thin active semiconductor region, a high carrier density and a high room-temperature mobility. The best materials are narrow-gap III-V compounds. 2DEG layers in InSb and InAs would be ideally suited for these devices. The accumulation layer at the surface of InAs has been used to make magnetoresistors, Hall sensors and magnetotransistors. n-type doped thin InSb films are used to make magnetoresistors that outperform Si-based Hall sensors, even with integrated amplification. The authors describe device design criteria, materials requirements and a direct comparison of the three types of galvanomagnetic devices, magnetoresistors, Hall sensors and magnetotransistors, made from the same material. They compare the output of different magnetic field sensing technologies, such as Si and GaAs Hall sensors, and NiFe-based magnetoresistors, with InSb magnetoresistors.