Trap studies in GaInP/GaAs and AlGaAs/GaAs HEMT's by means oflow-frequency noise and transconductance dispersion characterizations

The presence of traps in GaInP/GaAs and AlGaAs/GaAs HEMT's was investigated by means of low frequency noise and frequency dispersion measurements. Low frequency noise measurements showed two deep traps (E _a1=0.58 eV, E_a2=0.27 eV) in AlGaAs/GaAs HEMT's. One of them (E_a2) is responsible for the channel current collapse at low temperature. A deep trap (E_a1'=0.52 eV) was observed in GaInP/GaAs HEMT's only at a much higher temperature (~350 K). These devices showed a transconductance dispersion of ~16% at 300 K which reduced to only ~2% at 200 K. The dispersion characteristics of AlGaAs/GaAs HEMT's were very similar at 300 K (~12%) but degraded at 200 K (~20%). The low frequency noise and the transconductance dispersion are enhanced at certain temperatures corresponding to trap level crossing by the Fermi-level. The transition frequency of 1/f noise is estimated at 180 MHz for GaInP/GaAs HEMT's and resembles that of AlGaAs/GaAs devices     

L- and S-band low-noise cryogenic GaAs FETamplifiers

The authors present the results of the construction and testing of three cryogenic low-noise GaAs FET amplifiers, based on a National Radio Astronomy Observatory design, to be used in a detector for the axion, a hypothetical particle. The amplifiers are centered on 1.1 GHz, and 2.4 GHz, have a gain of approximately 30 dB in bandwidths of 300 MHz, 225 MHz, and 310 MHz, and have minimum noise temperatures of 7.8 K, 8 K, and 15 K, respectively     

Characterization of a quasi-optical NbN superconducting HEB mixer

In this paper, the performance of a quasi-optical NbN superconducting hot-electron bolometer (HEB) mixer, cryogenically cooled by a close-cycled 4-K refrigerator, is thoroughly investigated at 300, 500, and 850 GHz. The lowest receiver noise temperatures measured at the respective three frequencies are 1400, 900, and 1350 K, which can go down to 659, 413, and 529 K, respectively, after correcting the loss and associated noise contribution of the quasi-optical system before the measured superconducting HEB mixer. The stability of the quasi-optical superconducting HEB mixer is also investigated here. The Allan variance time measured with a local oscillator pumping at 500 GHz and an IF bandwidth of 110 MHz is 1.5 s at the dc-bias voltage exhibiting the lowest noise temperature and increases to 2.5 s at a dc bias twice that voltage.     

Thermal effects in JFET and MOSFET devices at cryogenic temperatures

Various JFET and MOSFET devices have been studied at LN and LHe temperatures. Transient and steady-state heating of the devices at 4.2 K is investigated and it is found that the active part of the device typically heats to a steady-state temperature of 40-60 K. A transient and steady-state heating model of the device is constructed and the results are found to be in good agreement with the measured temperatures and heating transients. Studies of the noise at the various ambient temperatures show that different physical phenomena are responsible for the noise. Low-frequency noise in JFET's seems to be of generation-recombination type. Thermal noise is prevalent in the frequency region between 100 kHz and 1 MHz. The noise in some of the MOSFET devices increases with decreased temperature and seems to be surface state or "flicker" noise, The noise in MOSFET devices is by factor 5-100 times larger than the noise in investigated JFET devices.     

A Cryogenically Cooled Two-Channel Paramp Radiometer for 47 GHz

A field operational radiometer for 47 GHz with 18 K cooled degenerate paramps is described which has parallel channels for two ortholinear or circular polarizations. It exhibits an instantaneous RF bandwidth of 300 MHz and a tuning range up to 2 GHz. Its double-sideband system noise temperature of 100 K at midband and its minimum rms noise fluctuation of 0.16 K are several times lower than those of existing millimeter wave receivers.     

Behaviour of a low-noise microwave f.e.t. at low temperature

The values of gain and noise figure at 1000 MHz were measured against temperature (from 300 to 77K) for a GaAs f.e.t., in common-source configuration. An important decrease in noise figure from 3.2 to 1.5 dB with a 2 dB increase in gain was observed.     

Impedance and noise in the channel of a GaAs Schottky-gate field-effect transistor

The behaviour of the impedance and noise of the channel of a GaAs Schottky-gate field effect transistor is experimentally analyzed in the temperature range 77–300K and in the frequency range of 150 to 900 MHz. The channel of the transistor (source and gate being short circuited) shows a thermal noise level in good agreement with van der Ziel's theory. At 77K, the observed excess of the noise temperature is attributed to an effect of hot carriers.     

Measurement of flicker phase noise of 1.4 GHz MESFET amplifier at temperatures between 300 K and 1.26 K

We have measured the phase noise of a low-noise 1.4GHz MESFET amplifier at temperatures between 300K and 1.26K and for sideband frequencies between 0.15 Hz and I kHz. In our experimental configuration the phase noise between 4.2 K and 2.17 K was large and mainly caused by bubbling of the liquid helium cryogen. However, the intrinsic phase noise, observed below 2.17 K, was lower than at room temperature, in contrast to earlier reported behaviour of amplifiers operated at X-band.     

LiNbO3:Fe,Zn晶体不同温度下的扇形噪音研究

研究了双掺LiNbO3晶体（LiNbO3：0．02wt％Fe，2 mol% Zn）常温和低温下的扇形光散射噪音。结果显示，LiNbO3：Fe，Zn晶体中的扇形噪音随时间的演化过程依赖于样品温度。在300-240K，扇形噪音强度经过一定时间达到极大值后将出现不同程度的减弱，减弱程度随温度的降低而减小；而在240～100K。扇形噪音强度在达到极大后不再出现明显的减弱现象。通过全息记录实验发现，不同温度下LiNbO3：Fe，Zn晶体中的扇形噪音对全息记录效果的影响基本相同。     

Low-Noise Cooled GASFET Amplifiers

Measurements of the noise characteristics of a variety of gallium-arsenide field-effect transistors at a frequency of 5 GHz and temperatures of 300 K to 20 K are presented. For one transistor type detailed measurements of dc parameters, small-signal parameters, and all noise parameters (T/sub min/, R/sub opt/, X/sub opt/ g/sub n/) are made over this temperature range. The results are compared with the theory of Pucel, Haus and Statz modified to include the temperature variation. Several low-noise ampifiers are described including one with a noise temperature of 20 K over a 500-MHz bandwidth. A theoretical analysis of the thermal conduction at cryogenic temperatures in a typical packaged transistor is included.     

Noise effects in bipolar junction transistors at cryogenic temperatures: Part II

In Part II of this investigation, a characterization of the output noise current generator i0of modern planar bipolar junction transistors (BJT's) for common-base configuration with the input ac open circuited is developed and verified at temperatures ranging from 60 to 300 K. It is shown that at low temperatures, for those devices where recombination processes in the emitter-base space-charge region become very pronounced, the resulting noise for these processes shows less than full shot noise. This noise reduction can show up at temperatures slightly below room temperature for such devices. (Generation-recombination effects described in Part I may still become important at temperatures below 110 K.) Also, it is demonstrated that an important parameter to monitor in taking these measurements, at least at low temperatures, is the alpha cutoff frequency fα if the low-frequency theory is to be realized.     

Radiometric observations of the 752.033-GHz rotational absorption line of H2O from a laboratory jet

The intensity and lineshape of the Doppler-broadened 752.033-GHz (2₁₁ ← 2₀₂) rotational transition of H₂O has been studied passively using a high-resolution two-stage heterodyne radiometer with single-sideband system noise temperature of 45,000 K. The purpose of the experiments was to demonstrate the observability at submillimeter wavelengths of a high-altitude rocket plume simulated by a laboratory H₂O jet in a vacuum chamber. First-stage mixing was accomplished by means of a GaAs Schottky diode with first local-oscillator power supplied by a CO₂-laser pumped formic-acid laser (761.61 GHz), generating and X-band IF signal. Second localoscillator power was provided by a tunable C-band source. One-MHz resolution capability was obtained by means of a 3-GHz waveguide cavity filter with only 9-dB insertion loss. In the H₂O jet experiments, the center frequency of the line was determined to within 1 MHz of the previously reported value. A rotational temperature ～ 75 K, a linewidth ～5 MHz, and a Doppler shift ～ 3 MHz (from a 45-degree rotation of the flow direction) were measured with the line-of-sight intersecting the jet axis at a distance downstream of 30 nozzle diameters. These absorption data were ogtained against continuum background radiation sources at temperatures of 1175 and 300 K.     

DC SQUID RF amplifiers

The noise and signal parameters of several types of RF amplifiers based on different SQUIDs with integrated and hybrid input coils were studied. A new type of multiloop DC SQUID with an integrated input coil and extremely low stray capacitances was designed. The inductance of a four-loop SQUID was 100 pH, the input coil inductance 1.3 nH, and mutual inductance 300 pH. The tuned integrated four-loop amplifier at 420 MHz had a noise temperature lower 0.5 K and a power gain of nearly 20 dB in a 60-MHz bandwidth. For the noise calibration of such amplifiers, SIS junctions were used as a shot noise source, or a cooled attenuator and a room temperature semiconductor noise source were used     

180–425 GHz low noise SIS waveguide receivers employing tuned Nb/AIO x /Nb tunnel junctions

We report recent results on a 20% reduced height 270–425 GHz SIS waveguide receiver employing a 0.49 µm² Nb/AlO _x /Nb tunnel junction. A 50% operating bandwidth is achieved by using a RF compensated junction mounted in a two-tuner reduced height waveguide mixer block. The junction uses an “end-loaded” tuning stub with two quarter-wave transformer sections. We demonstrate that the receiver can be tuned to give 0–2 dB of conversion gain and 50–80% quantum efficiency over parts of it's operating range. The measured instantaneous bandwidth of the receiver is ≈ 25 GHz which ensures virtually perfect double sideband mixer response. Best noise temperatures are typically obtained with a mixer conversion loss of 0.5 to 1.5 dB giving uncorrected receiver and mixer noise temperatures of 50K and 42K respectively at 300 and 400 GHz. The measured double sideband receiver noise temperature is less than 100K from 270 GHz to 425 GHz with a best value of 48K at 376 GHz, within a factor of five of the quantum limit. The 270–425 GHz receiver has a full 1 GHz IF passband and has been successfully installed at the Caltech Submillimeter Observatory in Hawaii. Preliminary tests of a similar junction design in a full height 230 GHz mixer block indicate large conversion gain and receiver noise temperatures below 50K DSB from 200–300 GHz. Best operation is again achieved with the mixer tuned for 0.5–1.5 dB conversion loss which at 258 GHz resulted in receiver and mixer noise temperature of 34K and 27K respectively.     

Conduction Mechanisms and Low-Frequency Electrical Noise Studies in pin InGaAs/InAlAs Strained MQW Photodiodes

The current–voltage (I–V) characteristics as a function of temperature of different strained multiple-quantum-well pin InGaAs/InAlAs photodiodes were investigated in the dark from 15 K to 300 K. Analysis of the slope variation of the I–V curves as a function of temperature, under forward bias, indicate a conduction mechanism by tunneling effect assisted by recombination centers. For temperatures below around 100 K, as the voltage increases, a negative resistance appears, followed by oscillations suggesting a sequential resonant tunneling between electronic states of the quantum wells. Low frequency electrical noise measurements performed at 300 K between 1 and$10^5$Hz confirm the existence of recombination centers.     

Noise parameters and light sensitivity of low-noise high-electron-mobility transistors at 300 and 12.5 K

The four noise parameters of cryogenically cooled HEMT's have been investigated. Two different HEMT structures, with and without spacer layer were tested. The noise parameters of both structures were similar at the room temperature, while they were dramatically different at cryogenic temperatures. The minimum noise temperatures measured at 8.4 GHz were 75 ± 5 K at the room temperature and 8.5 ± 1.5 K at the temperature of 12.5 K. The cryogenic performance is the best ever observed for field-effect transistors.     

Terahertz detection by GaN/AlGaN transistors

Detection of subterahertz and terahertz radiation by high electron mobility GaN/AlGaN transistors in the 0.2-2.5 THz frequency range (much higher than the cutoff frequency of the transistors) is reported. Experiments were performed in the temperature range 4-300 K. For the lowest temperatures, a resonant response was observed. The resonances were interpreted as plasma wave excitations in gated two-dimensional electron gas. Non-resonant detection was observed at temperatures above 100 K. Estimates for noise equivalent power show that these transistors can be used as efficient detectors of terahertz radiation at cryogenic and room temperatures     

Low noise GaAs varactor and mixer diodes prepared by molecular beam epitaxy

Schottky-barrier varactor and mixer diodes have been made from Ge-doped GaAs layers grown by molecular beam epitaxy. A microstrip parametric amplifier circuit incorporating a hyperabrupt varactor diode has given a noise temperature of 120 K and bandwidth of 180 MHz at 15 dB gain when pumped at 34 GHz, and a mixer diode mounted in a cryogenic receiver circuit had an s.s.b. noise temperature of 180 K at 90 GHz.     

125–170 GHz SIS-receiver with closed cycle refrigeration system

A mechanically tunable SIS receiver covering the frequency range from 125 to 170 GHz is described. For cooling at 2.8 K, a closed cycle refrigeration system has been developed that has a cooling power of 350 mW at 2.8 K. The IF is centered at 1.4 GHz with a bandwidth of 600 MHz. For preamplification, a cryogenic 2-stage HEMT amplifier has been developed that has a noise temperature of about 7 K. The best narrow-band spot noise temperature of the receiver is 28 K (DSB) at 133 GHz. Typical broadband (600MHz) values are between 50 and 200 K depending on the frequency. The receiver is used for radioastronomical measurements at the Cologne 3-m radiotelescope.     

Noise temperature variation with mount style

Noise temperatures in argon discharges at 1-20 torr in 0.63-cm inner radius tubes are presented. The noise temperatures measured at 147 MHz were dependent upon the noise-extracting electrode arrangements; this dependence resulted from a radial noise temperature variation within the discharges. The radial variation is expected to cause a frequency dependence in the microwave region.