GaAs Wafers Research Articles

Fabrication and characterization of thin film Ni–Cr resistors on MMICs

This paper investigates the design, fabrication, testing of Ni–Cr based thin film resistors (TFRs) with 80:20 ratio is fabricated on a 2 inch GaAs wafer for monolithic microwave integrated circuits (MMICs) applications. For the purpose of assessing the Ni–Cr TFRs performance in 3D MMICs, five resistors having size of 0.5, 1, 2, 4 and 8 squares and thickness of 30 nm each from five distinctive groups were measured. All the TFRs are measured with and without polyimide on top of these resistors. The TFRs with polyimide exhibits a minor increase in resistance value which is possibly due to the oxidation process during the curing of two layers of polyimides. On the other hand, great temperature solidness has been watched over the temperature examined and a greatest TCR of 60 ppm C−1 is achieved from room temperature to 150 °C.

GaAs wafers possessing facet-dependent electrical conductivity properties

Current-rectifying I–V curves have been recorded for {110}/{111} facet combination of a GaAs wafer, suggesting the fabrication of facet-controlled transistors.

Микроволновая вольт-импедансная спектроскопия полупроводников

We have tested experimentally the proposed method of microwave volt-impedance spectroscopy of semiconductors. The method allows to determine the local values of the semiconductor electrophysical parameters. The studies were performed on a homogeneous single-crystal GaAs wafer with a concentric antenna system formed on its surface. The resolution is determined by the diameter of the antenna central disk, which was amounted a = 12, 27, 57 μm. A constant bias voltage of 0 ≤ U ≤ 5 V was applied between the contact pads of the antennas. The complex impedance spectrum Z (f, U) of each antenna was measured using a Cascade Microtech probe station in the frequency range f = 0.1 - 10 GHz. The electrophysical characteristics of the semiconductor were determined from Z(f, U) spectra by the inverse problem solving. We have established the n-type for our semiconductor and determined the electrical potential difference on the metal-semiconductor interface. We have found as well the electron concentration, mobility and conductivity. Measurements of the same parameters by Hall four-probe method (giving the surface averaging) showed good mutual agreement of the results for the homogeneous sample under study.

Особенности газофазной эпитаксии GaAs на непланарных подложках

Abstract The features of the surface shape of GaAs epitaxial layers grown on grooves several micrometers wide with vertical walls and an aspect ratio close to unity are investigated. The grooves are formed on the surface of a GaAs wafer in a plasma-chemical etching installation and overgrown by organometallic vapor-phase epitaxy under reduced pressure in a reactor.

On-Chip Miniaturized Bandpass Filter Using GaAs-Based Integrated Passive Device Technology For L-Band Application.

In this work, a miniaturized bandpass filter (BPF) constructed of two spiral intertwined inductors and a central capacitor, with several interdigital structures, was designed and fabricated using integrated passive device (IPD) technology on a GaAs wafer. Five air-bridge structures were introduced to enhance the mutual inductive effect and form the differential geometry of the outer inductors. In addition, the design of the differential inductor combined with the centrally embedded capacitor results in a compact construction with the overall size of 0.037λ0 × 0.019λ0 (1537.7 × 800 μm2) where λ0 is the wavelength of the central frequency. For the accuracy evolution of the equivalent circuit, the frequency-dependent lumped elements of the proposed BPF was analyzed and modeled through the segment method, mutual inductance approach, and simulated scattering parameters (S-parameters). Afterward, the BPF was fabricated using GaAs-based IPD technology and a 16-step manufacture flow was accounted for in detail. Finally, the fabricated BPF was wire-bonded with Au wires and packaged onto a printed circuit board for radio-frequency performance measurements. The measured results indicate that the implemented BPF possesses a center frequency operating at 2 GHz with the insertion losses of 0.38 dB and the return losses of 40 dB, respectively, and an ultrawide passband was achieved with a 3-dB fraction bandwidth of 72.53%, as well. In addition, a transmission zero is located at 5.32 GHz. Moreover, the variation of the resonant frequency with different inductor turns and metal thicknesses was analyzed through the simulation results, demonstrating good controllability of the proposed BPF.

Wet etching generation of dislocation pits with clear facets in LEC-InAs single crystals

Dislocation etch pits with clear rectangular and elongated hexagonal shapes on indium arsenide (1 0 0) wafer surface have been obtained by carefully controlling the etch condition of HCl-based etchant with the addition of a surfactant. Etching activation energies of (1 0 0), (1 1 1)A and (1 1 1)B faces have been obtained by etching at different temperatures. The results suggest a chemically-controlled reaction restricted by the surfactant. Indices of the facet surfaces in the pits were analyzed with the aid of optical microscopy as well as pit side wall cross section observation by cleavage. It is similar to the etch pit facets of an In-doped GaAs wafer. Mechanism of the etching behavior of InAs has been discussed based on the results.

THE CURRENT–VOLTAGE CHARACTERISTICS OVER THE MEASUREMENT TEMPERATURE OF 60–400 K IN THE Au/Ti/n-GaAs CONTACTS WITH HIGH DIELECTRIC HfO2 INTERFACIAL LAYER

The Au/Ti/HfO2/[Formula: see text]-GaAs metal/insulating layer/semiconductor structures have been fabricated using standard thermal atomic layer deposition. We experimentally showed whether or not the HfO2 interfacial layer grown on the [Formula: see text]-GaAs wafer modifies the barrier height (BH) of the device at the room temperature. Besides, we investigated the measurement based on temperature dependence of the device parameters from the current–voltage ([Formula: see text]–[Formula: see text]) characteristics of the diode in 60–400[Formula: see text]K range with steps of 10[Formula: see text]K. The X-ray photoelectron spectroscopy (XPS) have been carried out to characterize the surfaces of both [Formula: see text]-GaAs wafer and HfO2 thin films. The series resistance value from the temperature-dependent [Formula: see text]–[Formula: see text] characteristics decreased with decreasing temperature, which is a desired positive result for the devices developed from the MOS capacitor. The BH value of 0.94[Formula: see text]eV (300[Formula: see text]K) has been obtained for the device with the HfO2 layer which is a higher value than the value of 0.77[Formula: see text]eV (300[Formula: see text]K) of the device without HfO2 layer. Therefore, we can say that the HfO2 thin layer at the metal/GaAs interface can also be used for the BH modification as a gate insulator for GaAs MOS capacitor and MOSFETs. When the temperature-dependent [Formula: see text]–[Formula: see text] characteristics at low temperatures have been considered, it has been observed that the current prefers to flow through the lowest BHs due to the BH inhomogeneities.

20-nm In0.8Ga0.2As MOSHEMT MMIC Technology on Silicon

High-gain millimeter-wave monolithic integrated circuit (MMIC) amplifiers have been developed, based on a planar metamorphic 20-nm gate length InGaAs metal–oxide–semiconductor high-electron-mobility transistor (MOSHEMT) technology on Si. Therefore, an Al2 O 3/Hf O 2 layer stack was deposited as a gate dielectric directly on top of an In0.8Ga0.2As channel by atomic layer deposition. The III–V heterostructure was epitaxial grown on a GaAs wafer and subsequently direct wafer bonded to a Si substrate, leading to a high-quality III–V channel formation on Si. The gate layout was optimized for millimeter-wave and submillimeter-wave integrated circuit applications using T-gates and wet chemical recess etching to minimize the parasitic gate capacitances. For a $2 \times 10 \,\,\mu \text{m}$ gate width transistor, a transit frequency $\text{f}_{\textrm {T}}$ of 200 GHz and a record maximum oscillation frequency $\text{f}_{\textrm {max}}$ of 640 GHz were extrapolated. A realized three-stage cascode amplifier circuit demonstrated a maximum gain of 21 dB at 278 GHz and a small-signal gain of more than 17 dB between 222 and 284 GHz. The total chip size of the millimeter-wave amplifier MMIC was only $0.5\,\,\times \,\,1.2$ mm2. To verify the RF performance of the III–V MOSHEMT on Si technology, all devices and circuits have been reproduced using an InGaAs MOSHEMT on GaAs technology, which has been processed simultaneously within the same wafer batch and achieved almost identical results.

Effect of Si Doping in Self-Assembled InAs Quantum Dots on Infrared Photodetector Properties

We investigate the characteristics of self-assembled quantum dot infrared photodetectors(QDIPs) based on doping level. Two kinds of QDIP samples are prepared using molecular beam epitaxy : n+-i(QD)-n+ QDIP with undoped quantum dot(QD) active region and n+-n−(QD)-n+ QDIP containing Si direct doped QDs. InAs QDIPs were grown on semi-insulating GaAs (100) wafers by molecular-beam epitaxy. Both top and bottom contact GaAs layer are Si doped at 2×1018/cm3. The QD layers are grown by two-monolayer of InAs deposition and capped by InGaAs layer. For the n+-n−(QD)-n+ structure, Si dopant is directly doped in InAs QD at 2×1017/cm3. Undoped and doped QDIPs show a photoresponse peak at about 8.3 μm, ranging from 6~10 μm at 10 K. The intensity of the doped QDIP photoresponse is higher than that of the undoped QDIP on same temperature. Undoped QDIP yields a photoresponse of up to 50 K, whereas doped QDIP has a response of up to 30 K only. This result suggests that the doping level of QDs should be appropriately determined by compromising between photoresponsivity and operating temperature.

Harmonic generation in the opaque region of GaAs: the role of the surface and magnetic nonlinearities.

Phase-locked second and third harmonic generation in the opaque region of a GaAs wafer is experimentally observed and analyzed both in transmission and reflection. These harmonic components, which are generated close to the surface, can propagate through an opaque material as long as the pump is tuned to a region of transparency or semitransparency and correspond to the inhomogeneous solutions of Maxwell's equations with nonlinear polarization sources. We show that measurement of the angular and polarization dependence of the observed harmonic components allows one to infer the different nonlinear mechanisms that trigger these processes, including not only the bulk nonlinearity but also the surface and magnetic Lorentz contributions, which usually are either hidden by the bulk contributions or assumed to be negligible. The experimental results are compared with a detailed numerical model that takes into account these different effects, including for the first time combined linear and nonlinear material dispersions in a nonlinear Lorentz oscillator model of the bulk nonlinearities. Our results suggest that the intensity of the second harmonic signal generated by the surface can be more intense than the signal generated by the bulk. These findings have significant repercussions and are consequential in nanoscale systems, which are usually investigated using only dispersionless bulk nonlinearities, with near-complete disregard of surface and magnetic contributions and their microscopic origins.

Understanding gaas Native Oxides By Correlating Three Liquid Contact Angle Analysis (3LCAA) and High Resolution Ion Beam Analysis (HR-IBA) to X-Ray Photoelectron Spectroscopy (XPS) as Function of Surface Processing

ABSTRACTChemical bonding in native oxides of GaAs, before and after etching, is detected by X-Ray Photoelectron Spectroscopy (XPS). It is correlated with surface energy engineering (SEE), measured via Three Liquid Contact Angle Analysis (3LCAA), and oxygen coverage, measured by High Resolution Ion Beam Analysis (HR-IBA).Before etching, GaAs native oxides are found to be hydrophobic with an average surface energy, γT, of 33 ± 1 mJ/m2, as measured by 3LCAA. After dilute NH4OH etching, GaAs becomes highly hydrophilic and its surface energy, γT, increases by a factor 2 to a reproducible value of 66 ± 1 mJ/m2. Using HR-IBA, oxygen coverage on GaAs is found to decrease from 7.2 ± 0.5 monolayers (ML) to 3.6 ± 0.5 ML. The 1.17 ratio of Ga to As, measured by HR-IBA, remains constant after etching.XPS is used to measure oxidation of Ga and As, as well as surface stoichiometry on two locations of several GaAs(100) wafers before and after etching. The relative proportions of Ga and As are unaffected by adventitious carbon contamination. The 1.16 Ga:As ratio, measured by XPS, matches HR-IBA analysis. The proportions of oxidized Ga and As do not change significantly after etching. However, the initial ratio of As2O5 to As2O3, within the oxidized As, significantly decreases after etching from approximately 3:1 to 3:2.Absolute oxygen coverage, as a function of surface processing, is determined within 0.5 ML by HR-IBA. XPS offers insight into these modifications by detecting electronic states and phase composition changes of GaAs oxides. The changes in surface chemistry are correlated to changes in hydro-affinity and surface energies measured by 3LCAA.

Ion-Implanted Photoresist Stripping by Using Organic Solvents

Various organic solvent-based mixture solutions were used to remove the ion-implanted photoresist on trench-patterned GaAs wafers. The mixture of acetonitrile (AcN) and dimethyl sulfoxide (DMSO) could remove bulk photoresist and crust but left a small amount of photoresist residue. However, the combination of AcN and DMSO with a small amount of HF completely removed high-dose ion-implanted photoresist even at 30 °C (ion-implantation dose of 5×1015 ions/cm2 and the energy of 70 keV). Moreover, there was no material loss of GaAs wafer observed in AcN+DMSO+HF solution during the removal of ion-implanted photoresist.

GaAs Q-switched Nd:CNGG lasers: operating at 4F3/2 → 2I11/2 and 4F3/2 → 2I13/2 transitions.

The nonlinear absorption properties of GaAs were measured at 1.06 and 1.34 µm by the open aperture Z-scan technique in this paper. Based on a neodymium doped calcium niobium gallium garnet (Nd:CNGG) disordered crystal grown by the Czochralski method, passively Q-switched lasers with the conventional GaAs wafer as the saturable absorber were demonstrated, operating on the transitions of 4F3/2 → 2I11/2 and 4F3/2 → 2I13/2. For the 4F3/2 → 2I11/2 transition, the laser operated at 1063 nm with a pulse duration of 546 ns and a repetition rate of 98.5 kHz. While for the 4F3/2 → 2I13/2 transition operating at 1340 nm, the minimum pulse width was 499.6 ns with the pulse repetition rate of 110.7 kHz.

Removal of high-dose P+ ion-implanted photoresist on GaAs in the mixture of dimethyl sulfoxide and acetonitrile

The mixture of dimethyl sulfoxide and acetonitrile removed the P+ ion-implanted photoresist on the GaAs wafer but left photoresist residues in the GaAs trench structures. When 1 vol% of HF was added to the solution, the ion-implanted photoresist on the trench-patterned GaAs prepared with the implantation dose of 5 × 1015 ions/cm2 at the implantation energy of 70 keV was completely removed, even at 30 °C. The enhancement of the ion-implanted photoresist removal efficiency is attributed to the increased interaction energy between the implanted photoresist and the solution that results from their similarities in the dispersive-to-polar component ratios.

Laser-driven semiconductor switch for generating nanosecond pulses from a megawatt gyrotron

A laser-driven semiconductor switch (LDSS) employing silicon (Si) and gallium arsenide (GaAs) wafers has been used to produce nanosecond-scale pulses from a 3 μs, 110 GHz gyrotron at the megawatt power level. Photoconductivity was induced in the wafers using a 532 nm laser, which produced 6 ns, 230 mJ pulses. Irradiation of a single Si wafer by the laser produced 110 GHz RF pulses with a 9 ns width and >70% reflectance. Under the same conditions, a single GaAs wafer yielded 24 ns 110 GHz RF pulses with >78% reflectance. For both semiconductor materials, a higher value of reflectance was observed with increasing 110 GHz beam intensity. Using two active wafers, pulses of variable length down to 3 ns duration were created. The switch was tested at incident 110 GHz RF power levels up to 600 kW. A 1-D model is presented that agrees well with the experimentally observed temporal pulse shapes obtained with a single Si wafer. The LDSS has many potential uses in high power millimeter-wave research, including testing of high-gradient accelerator structures.

Pump dependent carrier lifetimes in InAs/GaAs quantum dot photoconductive terahertz antenna structures

In this paper, we study the behavior of photoexcited carriers in GaAs wafers containing self-assembled InAs quantum dots (QDs). These samples were designed and grown to be employed as photoconductive antennae for terahertz (THz) generation. The implanted QDs serve to shorten the overall carrier lifetime and enable pumping with lasers operating at wavelengths between 1μm and 1.3μm. Optical pump-THz probe measurements reveal carrier lifetime shortening for higher pump powers in the unbiased antennae due to increased carrier capture via Auger relaxation. This phenomenon significantly broadens the THz spectra from QD-based PCAs and explains the increased THz intensity at higher frequencies presented earlier.

Arrival timing diagnostics at a soft X-ray free-electron laser beamline of SACLA BL1.

An arrival timing monitor for the soft X-ray free-electron laser (XFEL) beamline of SACLA BL1 has been developed. A small portion of the soft XFEL pulse is branched using the wavefront-splitting method. The branched FEL pulse is one-dimensionally focused onto a GaAs wafer to induce a transient reflectivity change. The beam branching method enables the simultaneous operation of the arrival timing diagnostics and experiments. The temporal resolution evaluated from the imaging system is ∼22 fs in full width at half-maximum, which is sufficient considering the temporal durations of the soft XFEL and the optical laser pulses.

The Growth of InAsxSb1 –x Solid Solutions on Misoriented GaAs(001) Substrates by Molecular-Beam Epitaxy

The effect of a substrate misorientation degree from a singular face on the composition and morphology of layers of InAsxSb1 –x solid solutions obtained by molecular-beam epitaxy on a GaAs surface has been investigated. The substrates of GaAs wafers with the orientation (100) misoriented in the direction [110] by 0°, 1°, 2°, and 5° are used. The heterostructures are grown at temperatures of 310°C and 380°C (respectively, the lower and upper boundaries of the temperature range in which structurally perfect InAsxSb1 –x films form). The effect of the molecular form of arsenic (As2 or As4) on the composition of the layers is studied. The composition and structural properties are investigated using high-resolution X-ray diffractometry (HRXRD) and atomic-force microscopy (AFM). It is established that, in the series of misorientation angles 0° → 5°, the arsenic fraction x increases consecutively when using fluxes of both As2 and As4 molecules. With the As2 molecular flux, the fraction x increases only a little (1.05 times) with increasing degree of misorientation, while, when using the As4 flux, the increase in x is 1.75 times. An increase in the growth temperature leads to growth in the arsenic fraction in the solid solution. The surface morphology improves with an increasing degree of misorientation at a low growth temperature and degrades at a high temperature.

Cross-section measurements and production of 72Se with medium to high energy protons using arsenic containing targets

Abstract Experiments were performed to evaluate production of 72Se, parent radionuclide of the positron emitter 72As, at high energy at the Brookhaven Linac Isotope Producer (BLIP). Excitation functions for 75As(p, xn)72/75Se in the 52-105 MeV energy range were measured by irradiating thin gallium arsenide (GaAs) wafers. Maximum cross section value for the natAs(p, 4n)72Se reaction in the energy range was 103±9 mb at 52±1 MeV. Production size GaAs and arsenic metal (As°) targets were irradiated with 136 μA and 165 μA beam current possessing an initial Linac energy of 117 MeV. A total of 3.77±0.1 GBq (102±3 mCi) of 72Se was produced from a GaAs target at a calculated target entrance energy of 105.4 MeV, and 13.8±0.3 GBq (373±8 mCi) of 72Se from an As° target at a calculated incident energy of 49.5 MeV irradiated for 116.5 h and 68.9 h, respectively.

Wet-chemical etching of GaAs(211)B wafers for controlling the surface properties

Substrate surface plays an important role to achieve high performance infrared devices and high-quality film layers. GaAs (211)B wafers were intensively used in infrared detector applications. Despite 'epiready' wafers can easily be found on the market, most of them have defects and contaminations due to their fabrication processes. The defects and contaminations on wafers may have deleterious effects on thin film growth and detector applications. To overcome such problems, various chemical treatments should be implemented prior to thin film growth. In this study, to understand the effect of wet chemical cleaning process on epiready (211)B GaAs wafers, piranha solution-based wet chemical etching was performed. After these treatments, the surfaces of GaAs wafers were investigated by atomic force microscopy and scanning electron microscopy. Energy dispersive X-ray spectroscopy was used to assess the chemical composition of the surface. The vibrational modes and two-dimensional maps were observed by a Raman spectroscopy.