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A study of the low-noise characteristics of AlSb/InAs and related high-electron mobility transistors (HEMTs) in the 6.1-A-lattice-constant material system is presented. The effect of gate bias is reported and comparisons are made to noise performance of several InAs-based HEMTs with different layer structure and channel composition.

The single-event effects response of three different III-V field-effect transistor technologies (GaAs MESFET, InAIAs/InGaAs HEMT, and AISb/InAs HEMT) is measured for MeV and GeV heavy-ion irradiation. These measurements reveal significant charge enhancement and very slow, microsecond-timescale relaxation times for the GaAs and InAIAs/InGaAs devices, with a much faster recovery from the ionizing event observed for the AISb/InAs HEMTs. Index Terms--AISb, charge collection, GaAs, HEMT, InAIAs, InAs, InGaAs, InP, MESFET, single-event transient, single-event upset.

Time-resolved charge-collection measurements performed on AISb/InAs/GaSb resonant interband tunneling diodes (RITDs) with pulsed laser excitation exhibit complex behavior as a function of the device operating point. A model considering conventional charge-collection principles in combination with transient band-bending effects is proposed to describe the experimental results. In the proposed model, a transient distortion of the band structure of the device (transient band bending) induced by holes trapped in the GaSb valence band well modulates the dc current through the RITD. The manner in which this transient modulation is manifested in the experimental observable depends sensitively on the operating point of the device, giving rise to qualitatively different temporal signatures under different dc bias conditions. Index Terms--Charge collection, high electron mobility transistor (HEMT), monostable-bistable transition logic element (MOBILE), resonant interband tunneling diode (RITD), resonant tunneling diode (RTD), single-event effects (SEEs), single-event upset (SEU), transient band bending.

Thick epitaxial layers of AlSb(Si) and AlSb (Be) were grown by molecular beam epitaxy and characterized by variable-temperature Hall/van der Pauw measurements. Results suggest Si as an acceptor in A1Sb with an energy level of 33 plusmn 4 whereas Be is also an acceptor with an energy level of 38 plusmn 4.

Research was conducted to examine the intermixing in As/Sb heterostructures through the characterization of a series of periodic (In,Ga,Al)-(As,Sb) structures wherein every ninth monolayer of Sb was substituted by As or vice versa. X-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy were used to characterize the superlattices that were developed by molecular beam epitaxy. Results indicate that Sb evaporation from the surface increases with increasing growth temperature for Sb monolayers in arsenides.

The Al(sub x)Ga(sub 1-x)Sb(sub y)As(sub 1-y)/InAs material system, where the lattice constant is near 6.1 angstroms, was used to study high efficiency mobility transistors with only InAs as the channel material. Their better InAs properties and the larger conduction band offset at the AlSb/InAs heterojunction demonstrate their potential for low-voltage, high-speed applications. The devices exhibit a transconductance of 600 mS/mm and an f(sub T) of 120 GHz at V(sub DS) = 0.6 V. With technological improvements, noise figures of 0.3 dB at 4 GHz and 0.6 dB at 10 GHz can be achieved.

A novel magnetoelectronic device for digital applications is presented, and characteristics of a Nonvolatile Random Access Memory (NRAM) cell are discussed. A prototype cell with micron dimensions and with binary output states of 0 and 80 mV has been demonstrated at room temperature. Device fabrication requires only two lithographic levels, one for a Hall cross and one for an electrically isolated, microstructured bistable ferromagnetic film. Locally strong magnetic fringe fields from the edge of the film generate a Hall voltage in the semiconductor. The sign of the fringe field, as well as the polarity of the Hall voltage, is switched by reversing the in-plane magnetization of the ferromagnet. The device is inverse scalable: output characteristics improve as dimensions shrink. A high-density, solid state NRAM with nsec read, write and access times could replace both DRAM and magnetic disk drives in most computer environments, eliminating redundancy in memory systems.

Use of a semiconductor-insulator-semiconductor (SIS) heterostructure to determine Si/Si(1-x)Ge(x) valence band discontinuity on (100) unstrained Si indicates that the bottom Si/Si(1-x)Ge(x) interface has a low valence band discontinuity when the Ge composition exceeds 10%. The application of a new data analysis method helps derive the valence band discontinuity values. An experimental evaluation of the discontinuity shows a value of 6.4x million electron volts for Ge compositions ranging between 0% and 17.5%.

The optimal epilayer thicknesses for InxGa1-xAs and InyAl1-yAs alloys were investigated using high-resolution x-ray diffraction (HRXRD). Alloy samples were epitaxially grown on Fe-doped (001) InP substrates at a temperature range of 460 to 510 degrees centigrade. The structures were then characterized by HRXRD to deternmine the layer composition and strain. Results reveal the presence of an epilayer thickness range over which a single HRXRD scan yielded the composition of InxGa1-xAs and InyAl1-yAs layers to within one percent.

Research was conducted on mismatched InGaAs/InP and InAlAs/InP epitaxial layers possessing high crystalline properties using molecular beam epiitaxy. Layer quality, compositiion and strain were determined via high-resolution x-ray diffraction. Results showed that the crystalline quality of the heterostructures was relatively high in lattice mismatches of approximately 1%.The experimental data are intended to be used for the development of high-performance mismatched InAlAs/InGaAs/InP heterostructure field-effect transistors.

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]

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.

Time-resolved charge-collection measurements are performed on AlSb/InAs HEMTs with pulsed laser excitation as a function of device bias conditions and the incident laser pulse energy. The results provide clear evidence for the presence of charge-enhancement processes that, in many ways, are analogous to those observed previously for GaAs FET technology.