Nb/GaAs super-Schottky diode

A super-Schottky contact diode made of Nb on heavily doped p-GaAs has been fabricated by electron-beam deposition under high vacuum, resulting in a rugged device having very reliable characteristics with detector current sensitivity S ≃ 1500 V^-1and estimated NEP ≃ 1.2 × 10^-15W/√HZ at 4.2 K under the optimum bias conditions.     

Frequency measurements of optically pumped far-infrared laser lines

In this work, we report the frequency measurements of optically pumped far-infrared (FIR) laser lines. We use the heterodyne technique of mixing FIR laser radiation and microwave radiation on a metal-insulator-metal (MIM) point contact tunnel diode, to determine the FIR laser frequencies. The two FIR laser systems, consisting of CO₂ waveguide pump lasers and Fabry-Perot FIR laser cavities, and MIM diode were developed by us. To check the system, we have measured some FIR laser line frequencies previously reported in the literature. An average fractional frequency reproducibility of ±7×10^-7, between our measurements and the previous ones, permit us to use our system to measure five new FIR laser frequencies     

Development of Heterojunction Diode-Type Gamma Ray Detectors Based on Epitaxially Grown Thick CdTe on$hboxn^+$-Si Substrates

Room temperature nuclear radiation detectors with energy discrimination capability developed by growing thick cadmium telluride (CdTe) epitaxial layers directly on n⁺-Si substrates in a metal-organic vapor phase epitaxy system is reported for the first time. The CdTe/n⁺-Si heterojunction diode detector exhibited good rectification and charge collection properties. The reverse leakage currents were typically 1times10^-7 to 5times10^-7 A/cm² at 50-V bias. The detector clearly demonstrated its energy discrimination capability by resolving gamma peak from the ²⁴¹Am radioisotope during radiation detection test at room temperature     

Microwave match of low-impedance thin-film Josephson junctions

It is demonstrated how a thin-film low-impedance Josephson junction can be matched in a rectangular waveguide at 9 GHz, thus reducing the necessary power in voltage standard applications by a factor of 250. The method is also applicable to higher frequencies and to microwave devices such as detectors and mixers.     

Electrooptic effects in an InGaAs/InAlAs multiquantum wellstructure

The field-induced refractive index change of an InGaAs/InAlAs MQW waveguide is examined for various wavelengths and TE/TM modes using a MZ modulator. The quadratic EO coefficients in the MQW waveguide for both TE and TM modes due to quantum confined Stark effect (QCSE) is on the order of 10^-18 [m²/V²], which is dominant compared with the linear EO effect. An effective linear EO effect, however, is significant because of the bias field arising from the built-in potential. This effect is more than one order greater than the conventional laser EO effect, which may suggest new device applications for QCSE     

New developments in electromagnetic energy beaming

Current developments in large-aperture antennas coupled with the projected performance of high-power electron beam and solid-state devices for generation and rectification purposes, make it possible to greatly extend present capabilities of microwave/millimeter-wave beaming systems. These include greatly enhanced radar performance as well as some totally new applications of energy beaming. These extend over a large range of energy densities, all the way from 10^-10W/cm²typical of receiver sensitivities, to energy densities in excess of 10³W/cm²adequate for thermal interaction with many materials. This paper attempts to summarize some of the technology trends which support these applications, particularly in the areas of short range surveillance, space-space beaming, and some long range applications such as space based illumination. Some comparisons are also made with laser beaming, indicating the possible complementary use of both types of devices.     

All-silicon avalanche photodiode sensitive at 1.3 μm withpicosecond time resolution

The first experimental demonstration that an all-silicon photodiode can be used to measure the pulse shape of laser diodes emitting at 1.3 μm is reported. In order to allow for light absorption at these wavelengths, the bandgap narrowing phenomenon in heavily doped silicon is exploited. The device operates as a single photon detector in a time-correlated photon counting setup. The quantum efficiency of the detector (though only 10^-7), together with the very low noise (≈100 dark pulses per second) enable easy measurements on standard diode lasers. The use of standard silicon processing and the room-temperature operation are definite advantages of the device     

Sensitivity measurement of a 10.6-µm parametric upconverter

The sensitivity of a parametric upconverter for the detection of 10.6-µm radiation was measured. 10.6-µm radiation was mixed with the 1.06 µm beam of an Nd :YAG laser in properly oriented single-crystal proustite. The upconverted output at 0.967 µm was then detected by an S-1 photomultiplier tube. NEP of 1.1×10^-9W . s^½was measured.     

A novel voltage tuneable infrared spectrometer-detector

A novel voltage tuneable spectrometer-detector has been demonstrated whose principles are associated with the electric subbands existent at the interface between silicon and silicon dioxide. The photoresistive response of n-channel MOSFET structures to radiation resonant with energy levels in the inversion layer has been characterized and compared with existent theory. Operating at 4.2 K, typical devices have continuous tuneability from 8 MeV (∼150 µm) to 30 MeV (∼40 µm), a bandwidth of approximately 1 MeV, a response time of 2.5 × 10^-4s, and a noise equivalent power (NEP) of approximately 2.5 × 10^-10W/(Hz)^1/2limited by the available amplifiers.     

The optically pumped rubidium maser

The optically pumped rubidium maser oscillator is the most recent addition to a growing number of atomic frequency standards. It is the first atomic frequency standard which is small enough and simple enough to be considered as a replacement for crystal oscillators. These factors and the extreme phase stability which results from the maser action make this device unique among all frequency standards. The device generates a microwave output at the ground-state hyperfine frequency of Rb⁸⁷(6835 Mc/s). The maser consists of a microwave cavity filled with Rb⁸⁷vapor and nitrogen gas. Oscillation occurs when the vapor is illuminated with filtered rubidium resonance radiation. The power output of the maser is 10^-10watts, and higher powers can be expected. In this paper the physical principles and construction of the device are described. The effects of optical pumping, buffer gas, and temperature on the maser are discussed, and experimental results are given. The short-term stability for observation times of about one second is expected to be about one part in 10¹². This may be increased by an order of magnitude by increasing the powser output to 10^-8watts. The long-term stability is expected to be comparable to that obtained in the passive rubidium standard (about one part in 10¹¹per month). These slow fluctuations arise from pressure shifts, light shifts, cavity pulling, and changes in the chemical composition of the buffer gas. The long-term stability can be improved by using the rubidium maser as the flywheel for an atomic beam frequency standard. Such a combination could be expected to have both long-term and short-term stabilities as great as one part in 10¹³.     

100 GHz Binary counter based on DC SQUID's

A binary counter using bistable dc SQUID's as flip flop circuits is demonstrated. All of the functions: LOAD, COUNT, STORE, READ, and CLEAR can be performed. The use of single flux quantum logic results in high sensitivity (10^-18J input pulse energy), high speed (100 GHz count rate) and low power (10^-7W at 100 GHz count rate).     

High-speed demonstration of an output interface driver forsingle-flux quantum systems

The high-speed operation of a one-channel output interface for a single-flux quantum (SFQ) system has been demonstrated. The interface consisted of a Josephson latching driver, a room-temperature semiconductor amplifier, and a decision circuit module. The Josephson latching driver was fabricated by using a 2.5-kA/cm² standard Nb junction process and used to amplify an SFQ pulse into a 5.5-mV level signal at 10 Gb/s. The interface converted the SFQ pulse signal into a nonreturn-to-zero signal having an amplitude of 1 V at 10 Gb/s     

High-precision measurement of 2e/hthat uses cryogenic electronic components

A new determination of 2e/h is described, in which not only the Josephson junction but also the current-null detector and 100:1 ratio voltage divider are operated at 4.2 K. The results obtained with this new system are compared with previous data obtained with room-temperature components, and the agreement is found to be 0.02 (±0.05) parts in 106.     

Infrared detection by an atomic vapor quantum counter

An efficient technique for the detection of nartowband infrared radiation by up-conversion in an optically saturated atomic vapor is described. The strong transition cross sections provided by the resonance interactions combined with the narrow Doppler spectral response profile contribute to the potential to approach quantum-noise-limited performance. Experimental results confirm the model of the detection process for sodium transitions at 1.48, 2.34, and 3.42 μ. The predicted ultimate noise equivalent power (NEP) of this device is less than 10^-17W/Hz^1/2in the1.5-5-muspectral region.     

A model of the avalanche photodiode

A general model for the avalanche photodiode is presented. It is shown that the diode consists of four regions: 1) guard ring, 2) uniform avalanche region, 3) high-field absorption region and 4) zero-field absorption region. Expressions are given for the ac quantum efficiency, the dc quantum efficiency, and the transit time cutoff frequency. Material requirements are discussed. Based on an entire detector system, an expression is derived for the signal-to-noise ratio. An example is given with the result that a noise-equivalent power (NEP) of 10^-12W/Hz^1/2is obtained with an optimum avalanche gain of approximately 23.     

Low-frequency applications of superconducting quantum interference devices

The applications of Josephson junctions to the measurement of low-frequency magnetic fields and voltages are reviewed. The relevant ideas of flux quantization and Josephson tunneling are very briefly reviewed, and the various methods of making Josephson junctions mentioned. The two basic types of magnetic sensor, the dc superconducting quantum interference device (SQUID) and the RF SQUID, are described in some detail. Their theory of operation, noise limitations, and application to practical devices are discussed. The resolution of SQUID's commonly used in an analog mode is 10^-4to 10^-3Φ0/√Hz, where Φ0is the flux quantum. The basic sensor may be used in conjunction with a flux transformer to measure magnetic fields (with a resolution of 10^-14T/√Hz), magnetic-field gradients (with a resolution of 10^-12T/m/√Hz), and magnetic susceptibilities. The SQUID may also be used as a voltmeter. The resolution is limited by the Johnson noise developed in the resistance of the low-temperature circuit, provided that this resistance is not too large: the upper limit in the liquid-He⁴temperature range appears to be a few tens of ohms.     

Unloaded Q of Single Crystal Yttrium-Iron-Garnet Resonator as a Function of Frequency (Correspondence)

The practical feasibility of constructing magnetically tunable broad-tuning range microwave filters using single crystal yttriumiron-garnet resonators was demonstrated in a recent paper. Experimental results were presented on one- and two- resonator filters which can be tuned by varying a dc magnetic field bias over a full waveguide bandwidth and greater, at the same time maintaining an insertion loss performance which is comparable to mechanically-tuned cavity filters. The crucial parameter of the resonant elements in a band-pass filter is the unloaded Q, Q/sub u/. With a spherical single crystal of yttrium-iron-garnet the Q/sub u/ decreases with frequency below X-band frequencies reaching very low values at frequencies around 2000 Mc.     

Advances in SQUID magnetometers

The operation and noise limitations of de and RF SQUID's are outlined, and recent advances in their sensitivity are discussed. A model of the dc SQUID predicts an energy noise level per hertz referred to the SQUID of approximately8 k_{B}TL/R approx 8 k_{B}T(piLC)^{1/2}, whereL, R,andCare the SQUID inductance and the shunt resistance and capacitance of each Josephson junction. Some examples of dc SQUID's are described to show that their performance is generally in reasonable agreement with the model. The noise energy has improved from about 2 × 10^-30J. Hz^-1for a device withL = 1nH and a tunnel junction area of 10⁴µm²to about 2 × 10^-33J . Hz^-1for a device withL = 0.1nH and a microbridge resistance of 40 Ω. Further improvements axe expected in the near future. The model of the RF SQUID predicts a noise energy per hertz referred to the SQUID of[(pialpha^{2}phimin{0}max{2}/2L) + 2 pi alpha k_{B}Tmin{a}max{(eff)}]/omega_{RF}, where α is the intrinsic width of the distribution of flux transitions,Tmin{a}max{(eff)}is an effective amplifier noise temperature, and ωRFis the pump frequency. With one exception, the performance of the seven types of RF SQUID listed is in reasonable agreement with the model. The noise energy ranges from about 1.5 × 10^-29J . Hz^-1for a 20-MHz toroidal SQUID to 3.5 × 10^-31J . Hz^-1for 9-GHz reentrant toroidal SQUID; a somewhat better sensitivity has been reported for a 430-MHz device, apparently in conflict with the theory. In both dc and RF SQUID's, 1/fnoise (fis frequency) is likely to extend to higher frequencies as the white-noise level is decreased.     

The silicon cryosar at microwave frequencies

Microwave and low-frequency measurements are reported onn^{+}-v-n^{+}silicon cryosars fabricated with narrow intrinsic region widths. The low-frequency measurements includeV-Idata with and without incident microwave power. The electric field required to cause impact ionization of the donors was found to be greater than 10⁵V/m. The microwave measurements include a demonstration of mixing, harmonic mixing, and harmonic generation. Small-signal impedance measurements as a function of bias are reported at 1.33 and 3.05 GHz, and the diode noise temperature was measured to be 16 000 or 3000 K depending on bias polarity. Mobile electron lifetime is 10^-10s.     

Radiation detection with the pyromagnetic effect

The dynamic pyromagnetic response of several materials with magnetic phase transitions near 300°K has been measured by a method initially described by Chynoweth [1]. The results indicate that practical broad-band pyromagnetic radiation detectors operating in a fast dynamic thermal mode are possible. The best results were obtained with gadolinium and manganese germanide crystals which have second-order magnetic phase transitions slightly below 300°K. Their responses peaked at 300°K, but remained high over fairly large temperature ranges, a 25°C interval in the case of gadolinium. The NEP of ∼ 10^-8W.Hz^-1/2(0.12 cm²active area) obtained with gadolinium is larger by a factor of 10 than that reported for 300°K pyroelectric detectors, but was limited by laboratory noise pickup in the detector coil rather than the internal Johnson noise. Improved techniques should result in lower NEPs. The pyromagnetic responses at the critical temperatures of two materials with first-order magnetic phase transitions, FeRh and MnAs, were considerably smaller than expected. They were also anomalously discontinuous compared with the measured step in the static magnetization. A third material, Fe.71Mn1.44As, with a first-order transition at 344°K, gave a much larger response, but over a very narrow temperature range.