GaAs slow-wave phase shifter characteristics at cryogenic temperatures

It has been previously demonstrated that a single elemental solid-state GaAs epitaxial device, based on slow-wave electromagnetic propagation, can provide substantial variable phase shift in the microwave frequency regime at room temperature. Further, it has been shown that the insertion loss L of the device is reduced by increasing the conductivity in the transmission line metallization. Low-temperature applications make it desirable to determine if such a device can operate at cryogenic temperatures demonstrating useful phase-shifting properties. We have developed an accurate reliable cryogenic experimental test setup and procedure capable of measuring the phase shift θ and insertion loss L of a 1.6-mm-long device embedded in a waveguide system several meters long. Measurements have been made at 4.2, 77, and 309 K over a frequency range from 2 to 18 GHz. The 300-K results agree extremely well with earlier work and substantiate that very accurate measurements in such a setup are possible. The cryogenic results at 77 K produce a differential phase shift of 155° compared to 229° at 300 K. Loss reduction is most dramatic at frequencies below about 14 GHz and becomes progressively less as 18 GHz is approached. For example, at a Schottky bias voltage of 0.5 V, L is reduced by a factor of 2.3, 2.2, and 2.4 at 2, 10, and 12 GHz, respectively. Similar loss reduction factors are found up to 14 GHz for the 0.0-V bias case. Device operation at 4.2 K produces a differential phase shift of 206° and not much change in loss values compared to 77 K.     

A hybrid phase shifter circuit based on TlCaBaCuO superconductingthin films

A superconductor-semiconductor hybrid reflection-type phase shifter circuit has been designed, fabricated, and characterized for 180° phase bit with center frequency of 4 GHz and bandwidth of 0.5 GHz for operation at 77 K. All of the passive components of the phase shifter circuit such as input/output feed lines, 3 dB Lange coupler, impedance matching networks, and transmission lines consisted of thallium based superconducting TlCaBaCuO thin films of 4000 Å thickness on lanthanum aluminate substrate. Metal-Schottky field-effect-transistors (MESFET's) on GaAs semiconductor were used as active devices for switching action (on-state and off-state) in the phase shifter circuit. The phase shift and insertion losses were investigated as a function of frequency from 3.6 to 4.6 GHz at 77 K. The circuit exhibited a fairly flat response of 180° phase shift with a maximum deviation of less than 2° and a maximum insertion loss of 2 dB for on-state and 2.2 dB for off-state conditions over 0.5 GHz bandwidth at 4 GHz. The insertion losses were also fairly flat within the bandwidth. The insertion losses were constant between 50 and 80 K, giving the circuit a large range of operation at or below 77 K. The performance of this circuit as compared to a gold microstrip-semiconductor circuit designed identically was superior by a factor of 1.5, and may be due to lower conductor losses and lower surface resistance in the superconducting microstrips     

Temperature dependence of specific contact resistivity

The temperature dependence of specific contact resistivity has been measured over the range 77-380 K for W contact to both B- and P-doped silicon. A range of surface concentrations have been investigated. In general, ρcis slightly more weakly temperature dependent than has been predicted. There appears to be no fundamental barrier to obtaining low-resistance contacts for low-temperature (<100 K) device operation. Contact resistivity to very heavily P-doped surfaces actually decreases with decreasing temperature, in agreement with predictions.     

The influence of γ-ray radiation on electrical properties of CuGaSe<Subscript>2</Subscript>

The effect of γ-ray radiation on the conductivity of low-resistivity (10²2–10⁴ Ω cm) and high-resistivity (10⁵–10⁷ Ω cm) CuGaSe₂ single crystals has been studied in the temperature range 77–330 K. It is found that the resistivity of low-resistivity samples increases as the dose of γ-ray radiation is increased, while the resistivity of high-resistivity samples is practically independent of the radiation dose. It is assumed that a decrease in the conductivity of the low-resistivity samples occurs owing to scattering of free charge carriers at defects (charged centers) formed as a result of irradiation with γ-ray photons. It is found that the dose of the γ-ray irradiation does not affect the temperature dependence of resistivity in the low- and high-resistivity samples in the temperature range 77–300 K.     

C49 defect influence on the C49–C54 transition

The C49–C54 transformation has been studied in TiSi₂ thin films having different concentration of defects. The defect concentration in the C49 phase has been varied using different thermal processes in the 460–540 °C temperature range; in fact, the defect concentration decreases with increasing the temperature and/or the duration of the thermal process as attested by the large variation of the silicide residual resistivity at 4 K. The kinetics of the transformation at 650 °C has been followed by in situ resistivity measurements and, for each sample, the transition time decreases as the defect concentration in the metastable phase decreases.     

Electron drift velocity in GaAs using a variable frequency microwave time-of-flight technique

A modified form of microwave time-of-flight technique has been developed which uses a variable frequency microwave deflection system to modulate the electron beam. This enables electron drift velocities to be measured absoslutely over a wide range of values whereas previous microwave time-of-flight measurements have given only relative velocities and require at least one point of normalisation. This new technique has been applied to measure the drift velocity of electrons in n-type GaAs for electric fields up to 135 kV cm^?1 and over the temperature range 77–400 K. For fields above 10 kV cm^?1, excellent agreement is obtained with conventional time-of-flight measurements.     

InGaAs/InP微波双极型晶体管的研制

本文叙述双收集区NpnN型InGaAs/InP异质结双极型晶体管的实验结果.给出器件的击穿特性、开关特性.高频特性和温度特性.理论分析和实验结果表明,n型InGaAs第一收集区的厚度对晶体管的击穿特性和开关特性有重要影响.器件的击穿电压BV_(CE0)=20伏,贮存时间t_s=0.5ns(Ic=50mA,I_(B1)=10mA,回抽电流I_(B2)=0),f_T=1.2GHz(V_(CE)=6V,Ic=15mA).在77～433K范围内h_(fe)变化很小,在4K下h_(fe)≌1,并表现出强烈的俄立(Early)效应.     

Interphase interactions and the mechanism of current flow in Au-TiB x -AuGe-n-GaP ohmic contacts

Au-TiB _x -AuGe-n-GaP ohmic contacts have been investigated before and after rapid thermal annealing at T = 723, 773, and 873 K for 60 s in a hydrogen atmosphere. It is shown that the contact resistivity decreases with an increase in temperature in the range 77–232 K due to the thermionic nature of current flow in inhomogeneous ohmic contacts, while in the range 232–386 K the contact resistivity increases, which can be related to the conduction through metal shunts.     

Effect of the deposition rate on the phase transition in silver telluride thin films

Silver telluride thin films of thickness 50 nm have been deposited at different deposition rates on glass substrates at room temperature and at a pressure of 2×10⁻⁵ mbar. The electrical resistivity was measured in the temperature range 300–430 K. The temperature dependence of the electrical resistance of Ag₂Te thin films shows structural phase transition and coexistence of low temperature monoclinic phase and high temperature cubic phase. The effect of deposition rate on the phase transition and the electrical resistivity of silver telluride thin films in relation to carrier concentration and mobility are discussed.     

BILOW-simulation of low-temperature bipolar device behavior

The BILOW simulation program for investigating bipolar transistor behavior in the temperature range 77-300 K is discussed. Differences between the numerical approaches required for simulation of low-temperature behavior compared to room-temperature simulation are presented. Efficient numerical models for the physical parameters in the carrier transport equations and Poisson's equation for the temperature range of 77-300 K, including a new highly accurate numerical model for the temperature and doping concentration dependence of carrier mobility, are discussed. A temperature- and doping-concentration-dependent model for apparent bandgap narrowing is also discussed. The internal characteristics of a typical bipolar transistor are simulated over the 300-77 K range. The behavior of current gain β and the unity gain frequency f_T versus collector current density for different temperatures are calculated and discussed     

Temperature effects in bulk GaAs amplifiers

The microwave-gain characteristics of a bulk GaAs amplifier have been investigated experimentally as a function of temperature. The resistivity of the samples showed a strong temperature dependence, hence the results have been interpreted in terms of changing carrier concentration assuming a constant mobility. It has been found that stable amplification only occurs within a narrow range of temperature (carrier concentration). The highestn . Lproduct (carrier density × sample length) for which gain has been observed was about 5 . 10¹¹cm^-2, and this is in agreement with earlier results and theory. Amplification did not occur belown . L = 8 . 10^{10}cm^-2. The frequency band where negative conductance appears was found to be strongly dependent on temperature (carrier density) and bias field. Noise figures, measured at temperatures where gain occurred, lay between 20 and 30 dB. Noise figure appears to be nearly independent of temperature. Gain versus field measurements on a stable amplifier indicate that the peak field of the velocity-field curve is about 4000 V/cm. Gain versus frequency and noise figure have also been measured on a bulk semiconductor amplifier which was operated with a coaxial transformer to increase the gain over a broad microwave frequency range.     

Wavetilt Characteristics of EM Waves over a Homogeneous Earth Model

A theoretical analysis has been carried out to investigate the effect of resistivity, dielectric constant and angle of incidence on the amplitude and phase of the wavetilt over a homogeneous earth model over a range of frequency from very low frequency (VLF) to broadcast band (BCB). Numerical results for a wide range of above mentioned parameters are presented. Dependence of wavetilt on these factors has been discussed.     

Ferroelectric Phase Shifters for VHF and UHF

The analysis, construction, and performance of compact surface wave ferroelectric phase shifters suitable for operation in the100-to1000-MC frequency range are described. Although this ferroelectric loaded parallel-plane structure is a very low impedance structure, a satisfactory terminal impedance matching technique has been devised. Kilovolt level voltages are needed; but since the current required to maintain or rapidly shift phase is low, the over-all control power requirements are at least an order of magnitude less than those for comparable ferrite phase shifters. One of these room temperature operable phase shifters provided 348/spl deg/ of phase shift at 207 Mc. It had an insertion loss which varied from 3.7 to 2.2 db over a zero- to 4000-volt range of applied dc control voltage.     

Electrical properties of melt-grown silicon monoarsenide

Silicon monoarsenide crystallizes in the monoclinic structure and has an optical energy gap of 2·2 eV. Single crystal ingots of silicon monoarsenide have been grown by the Bridgman technique. These crystal cleaved readily along a ( 01) plane. The electrical resistivity and Hall coefficient of cleaved specimens have been measured over a wide temperature range. Silicon monoarsenide was found to exhibit very pronounced resistivity anisotropy, the resistivity along the direction perpendicular to the ( 01) being more than 500 times that along the b-axis. From the resistivity data, an acceptor level with an ionization energy of 0·135 eV was deduced, and the energy gap of silicon monoarsenide was determined to be 2·03 eV at 850°K.     

Window materials for high power gyrotron

The room temperature application of sapphire as window material at higher frequencies is not feasible since its absorption coefficient increases almost linearly with increasing frequency in the millimeter wavelength region. At cryogenic temperature the absorption coefficient value decreases only by a few factors (factor of 2 to 3) in the 90 – 200 GHz region. The earlier reported temperature squared dependence (decrease) in the absorption coefficient or the loss tangent value is totally absent in our broad band continuous wave data we are reporting here (at 6.5 K, 35K, 77K and 300K) and one we reported at conferences earlier. Our results are verified by another technique. We utilize our precision millimeter wave dispersive Fourier transform spectroscopic techniques at room temperature and at cryogenic temperatures The extra high resistivity single crystal compensated silicon is no doubt the lowest loss material available at room temperature in the entire millimeter wavelength region At higher millimeter wave frequencies an extra high resistivity silicon window or an window made with extra high resistivity silicon coated with diamond film would certainly make a better candidate in the future. A single free standing synthetic diamond window seems to have higher absorption coefficient values at millimeter wavelength region at this time although it is claimed that it possesses good mechanical strength and higher thermal conductivity characteristics. It certainly does not rule out the use of diamond film on a single crystal high resistivity silicon to improve its mechanical strength and thermal conductivity     

Cryogenic GaAs FET amplifier

An extremely low noise, cryogenic, gallium arsenide field-effect-transistor amplifier has been developed for the frequency range 3.7 to 4.2 GHz. The amplifier has an average noise temperature of 25 K, with an associated gain of 21 dB, when cooled to a physical temperature of 77 K.     

400 MHz-bandwidth all-fiber phase modulators with ZnO coating on standard telecommunication fiber

Miniature all-fiber phase modulators with a radially symmetrical piezoelectric ZnO jacket have been characterized over a wide frequency range up to 1 GHz. Multiple radial resonances with phase shift values as high as 0.82 rad were observed in the frequency region between 20-400 MHz. A linear dependence of the phase shift on the square root of the driving power is observed up to 125 mW with a phase shift efficiency of 0.21 and 0.175 rad//spl radic/mW per centimeter fiber length at 196.5 and 399.5 MHz, respectively. The dependence of the phase shift efficiency on the modulation length is demonstrated.     

Operation of poly bipolar transistors near liquid-heliumtemperatures (9 K)

Operation of bipolar transistors with poly emitters with current gain β>25 at 77 K and β>3 at 9 K has been demonstrated. In the temperature range of 300 K to 9 K, the plot of β vs. temperature (T) exhibits a minimum at T equal to 40 K: decreasing monotonically from 300 K to 40 K, remaining unchanged between 40 K to 30 K, and increasing slightly from 30 K to 9 K. This behavior is attributed to freezeout of acceptor impurities in the base for T<40 K     

Temperature behavior of spiral inductors on high resistivity substrate in SOI CMOS technology

This paper reviews and analyzes a compact model for integrated planar spiral inductors on standard and high resistivity substrates in silicon-on-insulator (SOI) technology. The inductors have been characterized over a temperature range from 25 to 200 °C. The temperature variation of each model parameter has been investigated. It demonstrates that only the variations of the metallic losses versus temperature have to be taken into account to model properly the high frequency behavior over a wide temperature range of a spiral inductor integrated on silicon high resistivity substrate. Based on these experimental and characterization results, guidelines for practical inductor designs in RFICs for high-temperature applications are drawn.     

High purity and chrome-doped GaAs buffer layers grown by liquid phase epitaxy for mesfet application

High purity GaAs buffer layers of carrier concentration in the low (l-5)×l0^l4/cm³ range with 77K electron mobility over 100,000 cm²/V-sec and 300K mobility around 8000 cm?/ V-sec have been grown by liquid phase epitaxy on Cr-doped GaAs substrates using the graphite sliding boat method. The high purity has been achieved with systematic and concurrent long term bake-outs (24 hrs) of both LPE melt and substrate, both exposed to the H₂ ambient gas stream at 775?C, prior to epitaxial growth at 700?C. Substrate surface degradation was reduced by using Ga:GaAs etch melts that were undersaturated at 700?C by 5? to 40?C. Best buffer layer morphologies with regard to surface planarity were obtained using etch melts that were saturated by near 85% of weight of GaAs at 700°C. The importance of substrate preconditioning in order to achieve the low ( 1 -2)×l0¹⁴ was examined and found to be critical. Melt and substrate bake outs at 800?C, and use of a 40?C undersaturated etch melt prior to epitaxial growth at 800?C resulted in a p-type layer of carrier concentration, 1 .9×l0^l2/cm³ and resistivity 1×10⁵ ohm-cm. Chromium doping at 700?C resulted in buffer layers with sheet resistivities greater than 10 ohms/sq and low pinhole densities.