SI-GaAs Substrate Research Articles

Low-actuation voltage RF MEMS shunt switch with cold switching lifetime of seven billion cycles

This paper investigates the performance and lifetime of a metal-to-metal shunt RF MEMS switch fabricated on an SI-GaAs substrate. The switch is a shunt bridge design that is compatible with standard microelectronic processing techniques. The RF performance of the switch includes actuation voltages of less than 15 V, isolation better than 20 dB from 0.25 to 40 GHz, and switching speeds of less than 22 /spl mu/s. Varying the geometry of the switch affects both switching voltage and reliability, and the tradeoffs are discussed. We have developed a cold switching test method to identify the root cause of sticking as a failure mechanism. The switch structure includes separation posts that eliminate sticking failure and has demonstrated lifetimes as high as 7/spl times/10/sup 9/ cold switching cycles. These results show that good reliability is possible with a metal-to-metal RF MEMS switch operated with a low actuation voltage.

Effect of proton implantation at variable temperatures and doses on the semi-insulating GaAs

The effects of proton irradiation on the electrical properties of semi-insulating gallium arsenide (GaAs) have been investigated to establish if deleterious effects are observed within the substrate following such carrier removal implants. Proton implantation was performed with doses from 1 × 10 12 to 1 × 10 16 cm −2 at 250 keV at room temperature (RT) and 200 °C. It was found that the SI GaAs does not become appreciably conductive after proton implantation for a dose range of 1 × 10 12–1 × 10 16 cm −2 for implants carried out at either RT or 200 °C and hence the material retains its semi-insulating behavior. Hot implants show better stability and optimization of sheet resistivity values. The temperature dependence of the sheet resistivity was also studied for the as-implanted and annealed samples. The data presented in this work is useful in order to interpret the isolation measurements of devices when the peak of the damage due to protons is placed within the SI GaAs substrate below the active device region.

Wafer-scale integration of GaAs optoelectronic devices with standard Si integrated circuits using a low-temperature bonding procedure

A methodology for the heterogeneous integration of epitaxial GaAs wafers with fully processed standard bipolar complementary metal-oxide-semiconductor Si wafers is presented. The complete low-temperature wafer bonding process flow, including procedures for the Si wafer planarization and GaAs substrate removal, has been developed and evaluated. The implementation of an in-plane optical link, consisting of an edge-emitting laser diode, a waveguide and a photodiode, is demonstrated.

Hole mobility in AlxGa1−xSb grown by metalorganic chemical vapor deposition

The temperature dependence of the hole mobilities of AlxGa1−xSb films in the regime 0⩽x⩽0.25 has been examined by Van der Pauw–Hall measurements. The films have been grown by metalorganic chemical vapor deposition on Si–GaAs substrates using TMAl, TMGa, and TMSb precursors. The mobility decreases sharply when a small amount of Al in the range 0<x<0.025 is incorporated into GaSb. The temperature dependence of mobility was analyzed using a model with contributions from various scattering mechanisms. At a low-temperature (<100 K), the mobility decreased due to a contribution from ionized-impurity scattering and in a high-temperature region (>100 K), the same effect was due to lattice phonon scattering. At 300 and 77 K, the alloy scattering is the most important mechanism in AlxGa1−xSb ternaries, however the temperature dependence of alloy scattering is less pronounced as the temperature decreases.

Characterization of a two-dimensional electron gas in an InSb/InAlSb heterostructure using surface acoustic wave attenuation

We have investigated the interaction between a surface acoustic wave (SAW) and the two-dimensional electron gas formed at the interface of InSb/InAlSb heterojunctions. The samples were grown by molecular beam epitaxy on (100) SI GaAs substrates. Measurements were performed with the SAW travelling along the [110] direction, and a numerical approach was used to calculate the appropriate SAW coefficients. Along [110] a leaky SAW solution exists, with a piezoelectric coupling coefficient K2eff of 3.52 × 10−4, and velocity of 2680 m s−1. At high magnetic fields Shubnikov–de Haas-like oscillations were observed in the SAW attenuation and phase shift that reflect the oscillating magnetoresistance, and a quantitative analysis of the oscillations yields reasonable values for the electron concentrations. The best defined oscillations were observed in measurements on the sample with the lowest doping.

MOCVD Growth and Characterization of InNAs/GaAs Quantum Wells

ABSTRACTInNAs/GaAs multiple-quantum-wells were grown by MOCVD on (100) SI-GaAs substrates using trimethylindium, tertiarybutylarsine, and 95–97.5% of dimethylhydrazine (DMHy) in the vapor phase. The crystalline quality and solid phase composition were evaluated using highresolution x-ray diffraction analysis. Nitrogen content in InNAs wells was determined to be 28%. Electron energy loss spectroscopy was used to confirm the presence of nitrogen in quantum wells. Surface morphology was investigated by atomic force microscopy (AFM) and field emission microscopy (FEM).

Piezoelectric photothermal study of AlxGa1−xAs epitaxial layer (x=0.22, 0.28, and 0.5) grown on semi-insulating GaAs substrate

Piezoelectric photothermal measurements of an AlxGa1−xAs (x=0.22, 0.28, and 0.5) epitaxial layer grown on a GaAs substrate were carried out in the temperature range of 297 to 80 K. In addition to the band gap signal of the GaAs substrate, the direct transition gaps of AlGaAs were clearly observed in the higher photon energy region. It was experimentally confirmed that the temperature coefficient of the direct transition gap of AlxGa1−xAs alloy decreases with increasing Al mole fraction. By conducting the quenching light illumination measurements at 80 K we concluded that the photoexcited electrons in the AlGaAs epitaxial layer drifted under the influence of an electric field present at the AlGaAs/GaAs interface. The drifted electrons eventually recombined with the ionized EL2 centers in the SI GaAs substrate.

Ion bombardment in surface passivation of GaAs

The electrical properties of SI GaAs substrates after oxygen ion bombardment have been investigated in the temperature range of 150–373K. It was found that the oxygen ion bombardment of poor substrates stabilised their surface electrical properties in the sense of increase of the breakdown voltage. Because of leakage current which increased when the ion dose was increased only ion bombardment for the dose range from 1012 to 5×1012cm−2 may have a practical significance. However, the dose of ion bombardment of 1012cm−2 seems to be optimal. In this case the breakdown voltages were about 50V for a 20μm electrode separation (i.e. 25kV/cm) and leakage sheet current densities were from 3×10−9 to 5×10−8A/mm at the temperature range from 293 to 373K.

High performance 0.35 /spl mu/m gate-length monolithic enhancement/depletion-mode metamorphic In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As HEMTs on GaAs substrates

Monolithic integration of enhancement (E)- and depletion (D)-mode metamorphic In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As/GaAs HEMTs with 0.35 /spl mu/m gate-length is presented for the first time. Epilayers are grown on 3-inch SI GaAs substrates using molecular beam epitaxy. A mobility of 9550 cm/sup 2//V-s and a sheet density of 1.12/spl times/10/sup 12/ /sup -2/ are achieved at room temperature. Buried Pt-gate was employed for E-mode devices to achieve a positive shift in the threshold voltage. Excellent characteristics are achieved with threshold voltage, maximum drain current, and extrinsic transconductance of 100 mV, 370 mA/mm and 660 mS/mm, respectively for E-mode devices, and -550 mV, 390 mA/mm and 510 mS/mm, respectively for D-mode devices. The unity current gain cutoff frequencies of 75 GHz for E-mode and 80 GHz for D-mode are reported.

Study of As precipitates in LEC SI–GaAs wafer by Raman probe

As precipitates in the subsurface layer of LEC SI–GaAs substrates are characterized by Raman microprobe with a spatial resolution of 2 μm. We find that the LO line of GaAs at the As precipitate broadens asymmetrically because As precipitates and dislocations introduce disorder in the crystal. The compressive strain introduced by As precipitates results in the central frequency of LO line shifting to the blue.

New methods for the characterization of surface states density and substrate/epilayer interface states in pseudomorphic AlGaAs/InGaAs/GaAs heterostructures

Two new methods are presented for the characterization of the upper (dielectrics/semiconductor) and lower (epilayer/substrate) boundary conditions for devices using planar conduction in epilayers grown on SI-GaAs substrates. They make use of the same pseudomorphic AlGaAs/InGaAs/GaAs Hall heterostructures as test devices. They are used to investigate the electronic behavior of standard cleaned and ozone cleaned epilayer/substrate interfaces, and the density of states of surface states as well as their dynamic behavior.

Semi-insulating GaAs-based Schottky contacts in the role of detectors of ionising radiation: An effect of the interface treatment

Abstract It is generally agreed that the substrate material quality plays a key role in the performance of back-to-back detectors of ionising radiation based on semi-insulating (SI) material. The aim of this paper is to evaluate usually overlooked problem, namely the influence of the Schottky contact preparation on detector performance. We report on different approaches to modify and control the quality of the metal/SI GaAs interface via a treatment of the SI-GaAs surface by means of low-temperature hydrogen plasma and wet etching. The measured electrical and detecting properties of such structures display a strong dependence on the history and the way the GaAs surface is treated prior to the metal evaporation. We point out, therefore, that the semiconductor surface treatment before the Schottky metallization plays a role of comparable importance to the influence of the SI-GaAs substrate properties on detector performances.

Acoustic waves in finite superlattices: Influence of buffer layers

The influence of buffer layers on acoustic waves of shear horizontal polarization in finite superlattices is investigated here theoretically. Using a Green's-function method, we have obtained closed-form expressions of local and total densities of states as a function of the frequency \ensuremath{\omega} and the wave vector ${\mathbf{k}}_{\ensuremath{\parallel}}$ parallel to the layers. The expressions of the phonon trapping times are also derived and compared to the density of states. Due to the substrate/buffer layer/superlattice interaction, different kinds of localized and resonant discrete modes are found and their properties are investigated. In particular, we show the possibility of finding well-defined guided modes in the buffer layer or in the superlattice depending on whether the velocity of the transverse acoustic waves in the buffer is lower or higher than those in the superlattice and the substrate, respectively. These modes appear as well-defined peaks of the density of states and trapping times. Specific applications of our analytical results are given in this paper for a GaAs (Si) buffer layer embedded between a Si (GaAs) substrate and a finite GaAs-AlAs superlattice.

Surface and interface of [formula omitted] structures investigated by photoreflectance spectroscopy

Epitaxial layers of GaAs were grown by MOCVD technique on SI-GaAs substrates. Photoreflectance (PR) spectra were measured at room temperature for energies in the vicinity of the E 0 critical point for p-type as well as n-type doped GaAs SI-GaAs structures. Two experimental methods for the further investigation of the obtained PR spectra were proposed. The first method was based on the gradual chemical etching of the doped epilayer, the second on the PR measurements carried out for different wavelengths of the laser pump beam. Depending on the doping concentration, the existence of two PR subsignals was observed: the first arises from the surface space charge region, the second from the interface region. In the computational analysis of measured PR spectra Kramers-Kronig analysis of the complex photoreflectance function was applied.

A comparative study of Si and GaAs metal-semiconductor-metal photodetectors

In this paper we present a comparative study of the optical DC and transient properties of the Si- and GaAs-metal-semiconductor-metal photodetectors (MSM-PD's). The interdigitated metal fingers for the detectors were fabricated on n-type Si and semi-insulating GaAs substrates by using optical lithography and lift-off technique. The width and spacing of the interdigitated metal fingers varied between 1 and 2 μm, and the detector area varied between 100 × 100 μm2 and 500 × 500 μm2. For Si-MSM-PD's we used 150 nm thick aluminum and for GaAs-MSM-PD's 280 nm thick Ti/Pt/Au multilayer metallization for the Schottky barrier formation. The Schottky diode capacitance vs. bias voltage as well as dark and illuminated I-V characteristics as a function of optical power have been measured. Also the photoresponsivity vs. wavelength has been measured for various bias voltages. The speed of the detectors was studied by using a colliding pulse mode-locked laser. The experimental results show that the leakage currents in GaAs-MSM detectors are much smaller than in Si detectors, but still a reasonable photoresponsivity can be achieved also in Si detectors. The speed of the Si detectors could be improved by fabricating them on an epitaxial n+ - n− -structure, which results in a fast impulse response 625 ps (FWHM), 292 ps (fall time).

M/A-COM & the GaAs industry maturing together

M/A-COM has been servicing customers in the GaAs industry since 1979. For 17 years, it has been devoted to the growth and prosperity of the entire GaAs community. M/A-COM focuses solely on the supply of Semi-Insulating Gallium Arsenide (Si-GaAs) Substrates for integrated circuit applications. This article describes the history of M/A-COM as a substrate supplier, their facilities, technology, recent successes in the areas of crystal growth and surface properties and basic business philosophy.

Experimental study by “in situ” resistivity measurements of swift heavy ion induced defects in GaAs crystals

Gallium arsenide thin crystals were irradiated at GANIL with swift ions (oxygen, magnesium, argon, zinc, krypton, xenon) at various energies (0.13–5.7 GeV). From the DLTS spectrum, the introduced defects are shown to be point defects, similar to those obtained by fast electron and neutron irradiation. This study is concerned with extended results obtained from “in situ” resistivity measurements during 300 and 77 K irradiation. The investigated materials are LEC grown (Si-doped n-type and Zn-doped p-type) thinned crystals (6–300 μm thick) and, for the first time, epitaxial MOCVD n-type GaAs grown on SI GaAs substrates. Comparison of the various resistivity-fluence curves obtained for different ions and different energies shows a small dispersion for epitaxial material but a large one for LEC GaAs. The variations seem to be correlated with the electronic stopping power Se (in the range 1–20 MeV/μm) and suggest a slight defect annealing by electronic excitation.

S-Doped GaInAs Grown By Chemical Beam Epitaxy: Electrical And Structural Characterization

AbstractWe report on the electrical and structural characterization of sulfur (S) doped Ga0.73In0.27As layers, grown on SI (001) GaAs substrates by chemical beam epitaxy. The room temperature free electron concentration is 2×1017cm−3 while the corresponding value of mobility is 3400 cm2V−1 s−1. The epilayer is characterized by a deep trap, which could be attributed to the electrical activity of dislocations, with an activation energy of 0.59 eV and a capture cross section 6×10−15 cm2. TEM analysis shows that the GaInAs/GaAs interface is characterized by dislocation lines and loop-like configurations which could be attributed to climb movement by point defect absorption or emission. Annealing at 420°C (Ar ambient for 5 min) does not alter the carrier concentration (n) and mobility (μ) significantly. The invariance of n and μ, even though the temperature should be high enough to dissociate any Satomic hydrogen complexes, indicates that the number of hydrogen-S donor complexes in the as-grown material is small compared with the donor concentration. Finally, the effect of intentional atomic hydrogen diffusion is discussed.

A [formula omitted] structure in semi-insulating GaAs substrate by high energy implantation

A structure that consists of a semi-insulating layer over a buried n + layer ( SI n + ) has been obtained by MeV Si + implantation into SI-GaAs substrate and subsequently tailored by a very low dose O + implantation. This novel structure has been studied by measurements of current-voltage characteristics, electrochemical CV profiling and Hall effects. The results indicate that this structure is suitable for the provision of isolation, the fabrication of active devices and internal interconnections.

Generation of ultrashort electrical pulses with variable pulse widths

Electrical pulses from 450 fs to 3 ps are generated using coplanar strip lines and coplanar waveguides on SI GaAs substrate. We use two optical pump beams to generate two steplike electrical transients with opposite sign and then superimpose the signals resulting in rectangular shaped pulses. By varying the delay between the two pump beams the pulse width can be adjusted.