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We demonstrate the detection of a ferromagnetic domain wall using a nanoscale Hall cross. A narrow permalloy wire is defined lithographically on top of a Hall cross fabricated from an InAs quantum well. The width of the Hall cross (500 nm-1 μm) is similar to the width of the ferromagnetic wire (200-500 nm), and a geometric pinning site is fabricated in the ferromagnetic wire to trap a domain wall within the area of the Hall cross. The devices provide a signal that is often the same order of magnitude as the offset Hall voltage when a domain wall is located above the Hall cross, and may be useful for memory applications. Different geometries for the Hall cross and ferromagnetic wire are tested, and radiofrequency pulses are sent into the wire to demonstrate current driven domain wall motion. Further changes to the Hall bar geometry with respect to the wire geometry are investigated by numerical computation. A large gain in signal is seen for Hall bars only slightly wider than the ferromagnetic wires as compared to those twice as wide, as well as a larger sensitivity to the exact position of the domain wall with respect to the center of the Hall cross. [ABSTRACT FROM AUTHOR]

An understanding of the growth of (110) quantum wells (QWs) is of great importance to spin systems due to the observed long spin relaxation times. In this article, we report on the metamorphic growth and characterization of high mobility undoped InAs (110) QWs on GaAs (110) substrates. A low-temperature nucleation layer reduces dislocation density, results in tilting of the subsequent buffer layer and increases the electron mobility of the QW structure. The mobility varies widely and systematically (4000-16 000 cm2/Vs at room temperature) with deposition temperature and layer thicknesses. Low-temperature transport measurements exhibit Shubnikov de-Haas oscillations and quantized plateaus in the quantum Hall regime. [ABSTRACT FROM AUTHOR]

Transistors based on III-V semiconductor materials have been used for a variety of analog and high frequency applications driven by the high electron mobilities in III-V materials. On the other hand, the hole mobility in III-V materials has always lagged compared to group-IV semiconductors such as germanium. In this paper, we explore the use of strain and heterostructure design guided by bandstructure modeling to enhance the hole mobility in III-V materials. Parameters such as strain, valence band offset, effective masses, and splitting between the light and heavy hole bands that are important for optimizing hole transport are measured quantitatively using various experimental techniques. A peak Hall mobility for the holes of 960 cm2/Vs is demonstrated and the high hole mobility is maintained even at high sheet charge. [ABSTRACT FROM AUTHOR]

InxGa1-xSb is an attractive candidate for high performance III-V p-metal-oxide-semiconductor field effect transistors (pMOSFETs) due to its high bulk hole mobility that can be further enhanced with the use of strain. We fabricate and study InxGa1-xSb-channel pMOSFETs with atomic layer deposition Al2O3 dielectric and self-aligned source/drain formed by ion implantation. The effects of strain and heterostructure design for enhancing transistor performance are studied systematically. Different amounts of biaxial compression are introduced during MBE growth, and the effect of uniaxial strain is studied using wafer-bending experiments. Both surface and buried channel MOSFET designs are investigated. Buried (surface) channel InxGa1-xSb pMOSFETs with peak hole mobility of 910 (620) cm2/Vs and subthreshold swing of 120 mV/decade are demonstrated. Pulsed I-V measurements and low-temperature I-V measurements are used to investigate the physics in transistor characteristics. [ABSTRACT FROM AUTHOR]

We have studied the surface cleaning of Sb-based compound semiconductors using HF, NH4OH, and HCl cleans and the metal-oxide-semiconductor (MOS) capacitors fabricated subsequently. GaSb, InGaSb, and AlGaSb surfaces are investigated using low-energy radiation from the synchrotron. Capacitance-voltage (C-V) and photoluminescence measurements are carried out on capacitors made with Al2O3 from atomic layer deposition and corroborated with the results from synchrotron spectroscopy. Excellent C-V characteristics with a mid-band-gap interface state density of 3 × 1011/cm2eV are obtained on samples with the HCl clean. This is consistent with the finding that only the HCl acid clean is able to remove the native oxides present on GaSb and InGaSb surfaces, and produce clean and stable surfaces suitable for MOSFET development. Complete removal of AlOx on the AlGaSb surface was not possible using chemical cleaning. Termination of AlGaSb with two monolayers of GaSb is proposed as a solution. [ABSTRACT FROM AUTHOR]

A numerical technique is developed for the spatial localization of 1/f noise sources in AlSb/InAs high-electron-mobility transistors. The technique is based on the microscopic modeling of 1/f noise using the method of Langevin random sources, in which the noise sources are introduced nonuniformly throughout the device. An efficient algorithm is proposed for the determination of the spatial distribution of these noise sources and local (mesh point) values of the Hooge parameter. The algorithm takes advantage of the linearity between the terminal noise current and the power of the noise sources and uses an optimization approach based on linear least-squares minimizations to find the distribution from the experimental noise characteristics. The density of noise sources in the InAs channel is found to be much larger near the top interface than at the bottom interface. The local values of the Hooge parameter vary from 10-2 at the top to 3×10-4 at the bottom of the channel. [ABSTRACT FROM AUTHOR]

Photoreflectance (PR), a contactless form of electromodulation, is used in a study of the In[sub 1-x]Ga[sub x]Sb alloy series. The samples consist of epilayers of In[sub 1-x]Ga[sub x]Sb (0.780≤x≤0.900) grown by molecular beam epitaxy onto (100) GaSb substrates, resulting in percent mismatches between the substrate and layers ranging from 0.62% to 1.36%. These relatively small mismatches result in the epilayers being under a considerable amount of compressive stress. The effects of this strain field on the optical properties are seen through shifts and splittings of the PR spectra. These are exploited to determine the relative changes in the electronic band structure of the material. It is found that the shifting of the heavy-hole and spin orbit split off valence bands correspond well with the theory, while the light hole bands do not. A possible explanation for this is given. Results of a study of the compositional dependence of the In[sub 1-x]Ga[sub x]Sb energy gaps are also presented. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which grown epitaxial layers of some types of semiconductors by molecular beam epitaxy. Results and discussion; Summary.

Presents information on a study which investigated intermixing in arsenic/antimony heterostructures by characterizing a series of periodic structures. Experimental procedure; Results; Discussion.

Presents a study on optimal epilayer thickness for In[subx]Ga[sub1-x] and In[suby]Al[sub1-y]As compostion measurement by high-resolution x-ray diffraction. Introduction to high-resolution x-ray diffraction; Experimental design; Results and discussion.

Examines the impact of lattice mismatch on the structural properties of InGaAs and InAlAs epitaxial layers using high-resolution x-ray diffraction. Parameters that describe the mismatch between an epilayer and its substrate; Discussion on crystalline quality; Observations on the measurement of the epitaxial layer peak width.

Deals with a study which examined the photoreflectance of indium gallium arsenic and indium aluminum arsenic molecular beam epitaxy grown layers. Characteristics of the system; Experimental details; Results and discussions; Conclusions.

In this report, the authors investigate the use of H2/Ar-plasma exposure as a means for achieving high-quality electrical interfaces between p-type GaSb and atomic-layer-deposited Al2O3 dielectric films. Dry in-situ plasma treatments are shown to reduce the estimated density of interface states by over two orders of magnitude compared to a standard wet HCl-treatment, without increasing gate leakage. The chemical compositions of the natively oxidized and treated GaSb surfaces are analyzed via x-ray photoemission spectroscopy (XPS). XPS spectra indicate that the native GaSb oxide is segregated, with Sb-oxide compounds localized at the air interface. Effective H2/Ar-plasma treatments act to remove the Sb-oxide, resulting in a surface Ga-oxide layer enriched in Ga2O3. [ABSTRACT FROM AUTHOR]

In this letter we report the efficacy of a hydrogen plasma pretreatment for integrating atomic layer deposited (ALD) high-k dielectric stacks with device-quality p-type GaSb(001) epitaxial layers. Molecular beam eptiaxy-grown GaSb surfaces were subjected to a 30 minute H2/Ar plasma treatment and subsequently removed to air. Highk HfO2 and Al2O3/HfO2 bilayer insulating films were then deposited via ALD and samples were processed into standard metal-oxide-semiconductor (MOS) capacitors. The quality of the semiconductor/dielectric interface was probed by current-voltage and variable-frequency admittance measurements. Measurement results indicate that the H2-plamsa pretreatment leads to a low density of interface states nearly independent of the deposited dielectric material, suggesting that pre-deposition H2-plasma exposure, coupled with ALD of high-k dielectrics, may provide an effective means for achieving high-quality GaSb MOS structures for advanced Sb-based digital and analog electronics. [ABSTRACT FROM AUTHOR]

We investigate in-situ cleaning of GaSb surfaces and its effect on the electrical performance of p-type GaSb metal-oxide-semiconductor capacitor (MOSCAP) using a remote hydrogen plasma. Ultrathin HfO2 films grown by atomic layer deposition were used as a high permittivity gate dielectric. Compared to conventional ex-situ chemical cleaning methods, the in-situ GaSb surface treatment resulted in a drastic improvement in the impedance characteristics of the MOSCAPs, directly evidencing a much lower interface trap density and enhanced Fermi level movement efficiency. We demonstrate that by using a combination of ex-situ and in-situ surface cleaning steps, aggressively scaled HfO2/p-GaSb MOSCAP structures with a low equivalent oxide thickness of 0.8 nm and efficient gate modulation of the surface potential are achieved, allowing to push the Fermi level far away from the valence band edge high up into the band gap of GaSb. [ABSTRACT FROM AUTHOR]

Performance degradation due to interfacial traps is generally considered as one of the main challenges for III-V metal-oxide-semiconductor field-effect-transistors (MOSFETs). In this work, we have investigated the suppression of interface state response using band engineering in III-V quantum well MOSFETs and experimentally verified the concept in the antimonide materials system using a gate-stack consisting of Al2O3/GaSb/InAlSb. It is shown that if the thickness of the interfacial layer of GaSb is scaled down to a few monolayers, the effective bandgap of the interfacial layer increases dramatically due to quantum confinement, which leads to the suppression of interface-trap response. [ABSTRACT FROM AUTHOR]

The impact of <110> uniaxial strain on the characteristics of p-channel In0.41Ga0.59Sb quantum-well field-effect transistors (QW-FETs) is studied through chip-bending experiments. Uniaxial strain is found to affect the linear-regime drain current and the threshold voltage of the FET through the modulation of the hole mobility of the two-dimensional hole gas (2DHG) in the QW-FET. The piezoresistance coefficients of the 2DHG have been determined to be π∥<110>=1.17×10-10 cm2/dyn and π⊥<110>=-1.9×10-11 cm2/dyn. The value of π∥<110> is 1.5 times that of holes in Si metal-oxide-semiconductor (MOS) field-effect transistors and establishes InGaSb as a promising material system for a future III-V complementary MOS (CMOS) technology. [ABSTRACT FROM AUTHOR]

Quantum wells of InGaSb clad by AlGaSb were grown by molecular beam epitaxy. The InGaSb is in compressive strain, resulting in a splitting of the heavy- and light-hole valence bands and an enhancement of the mobility. The mobility was found to increase with increasing InSb mole fraction for values of strain up to 2%. Room-temperature mobilities as high as 1500 cm2/V s were reached for 7.5 nm channels of In0.40Ga0.60Sb. These results are an important step toward the goal of high-performance p-channel field-effect transistors for complementary circuits operating at extremely low power. [ABSTRACT FROM AUTHOR]

Deep level transient spectroscopy (DLTS) measurements have been made on GaAs n[sup +]p diodes containing GaSb self-assembled quantum dots and control junctions without dots. The self-assembled dots were formed by molecular beam epitaxy using the Stranski-Krastanov growth mode. The dots are located in the depletion region on the p side of the junction where they act as a potential well that may capture and emit holes. Spectra recorded for temperatures between 77 and 440 K reveal several peaks in diodes containing dots. A control sample with a GaSb wetting layer was found to contain a single broad high temperature peak that is similar to a line found in the GaSb quantum dot samples. No lines were found in the spectra of a control sample prepared without GaSb. DLTS profiling procedures indicate that one of the peaks is due to a quantum-confined energy level associated with the GaSb dots while the others are due to defects in the GaAs around the dots. The peak identified as a quantum-confined energy level shifts to higher temperatures and its intensity decreases on increasing the reverse bias. The activation energy for the quantum-confined level increases from 400 meV when measured at a low reverse bias to 550 meV for a large reverse bias. Lines with activation energies of 400, 640, and 840 meV are associated with defects in the GaAs based on the bias dependence of their peak positions and amplitudes. [ABSTRACT FROM AUTHOR]

Develops a magnetoelectronic device with microstructured ferromagnetic films. Production of Hall voltage in thin film semiconducting Hall bars; Impact of reversing the magnetization of ferromagnet on fringe field and output Hall voltage signs; Use of magnetoelectronic device as magnetic field sensor and logic gate.

Examines the phonons in quantum dots of InSb, GaSb and AlSb grown on gallium arsenide substrates by molecular beam epitaxy. Use of atomic force microscopy and Raman spectroscopy; Correlation between quantum dot and phonon mode; Attribution of two-mode behavior to the segregation of gallium into AlSb.

Examines the formation of nanometer-scale dots of indium antimonide, gallium antimonide, and aluminum antimonide on gallium arsenide substrates. Treatment of surface morphology as a function of growth temperature and monolayer coverage; Use of atomic force microscopy; Formation of a temperature window near congruent sublimation temperature.

Examines the interface control in indium arsenide/aluminum antimonide (InAs/AlSb) superlattices. Technique used in growing InAs/Alsb superlattices; Measurement of the interfacial control using X-ray diffraction and Raman spectroscopy; Role of growth temperature in achieving high-quality superlattices with AlAs bonds.

Examines the thermal stability of indium (In)-gallium-arsenic (As) and In-aluminum-As on In-phosphorus strained layers. Analysis on epilayer and interface quality as a function of annealing cycle; Use of high-resolution x-ray diffraction and electron mobility measurements; High crystalline quality retention of pseudomorphic heterostructures.

Examines the interface stoichiometry in indium arsenide/gallium antimonide superlattices grown by molecular beam epitaxy. Use of migration enhanced epitaxial techniques to prepare superlattices with indium antimonide and gallium arsenide-like interfaces; Factors allowing the use of x-ray diffraction and Raman spectroscopy to probe the structures.

Studies the epitaxial layers of In[sub x]Ga[sub 1-x]As grown on (001)InP by double-crystal x-ray diffraction. Use of variable azimuthal angle ellipsometry in the study; Optical anisotropy discovered in many samples.

In this report, we study the effectiveness of hydrogen plasma surface treatments for improving the electrical properties of GaSb/Al2O3 interfaces. Prior to atomic layer deposition of an Al2O3 dielectric, p-GaSb surfaces were exposed to hydrogen plasmas in situ, with varying plasma powers, exposure times, and substrate temperatures. Good electrical interfaces, as indicated by capacitance-voltage measurements, were obtained using higher plasma powers, longer exposure times, and increasing substrate temperatures up to 250 °C. X-ray photoelectron spectroscopy reveals that the most effective treatments result in decreased SbOx, decreased Sb, and increased GaOx content at the interface. This in situ hydrogen plasma surface preparation improves the semiconductor/insulator electrical interface without the use of wet chemical pretreatments and is a promising approach for enhancing the performance of Sb-based devices. [ABSTRACT FROM AUTHOR]

Lattice strain relaxation in InAs/GaSb heterostructures was investigated by x-ray diffraction. Two types of structures, grown by molecular beam epitaxy, are compared. In the first, GaSb buffer layers were grown on GaAs substrates, followed by 0.05–1.0 μm thick InAs layers. In the second, InAs layers were grown directly on GaSb substrates. For a given thickness, the InAs layers retain significantly more strain when grown on GaSb substrates, reflecting the lower threading dislocation density in the GaSb substrates relative to the GaSb buffer layers grown on GaAs. [ABSTRACT FROM AUTHOR]

Sheet carrier concentrations in quantum wells of InAs clad by AlSb were enhanced by modulation doping with very thin (9–12 Å) remote InAs(Si) donor layers. The growth temperature of the donor layers was a key parameter, with relatively low temperatures required to minimize Si segregation into the AlSb. Sheet carrier concentrations as high as 3.2×10[sup 12]/cm[sup 2] and 5.6×10[sup 12]/cm[sup 2] were achieved by single- and double-sided modulation doping, respectively. High electron mobility transistors fabricated using the modulation doped structure exhibited a unity current gain cut-off frequency of 60 GHz for a 0.5 μm gate length at a source-drain voltage of 0.5 V. [ABSTRACT FROM AUTHOR]