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The paper describes the practical realization and characteristics of a small, totally autonomous, passive frequency standard based on the coherent population trapping (CPT) phenomenon. A description of the frequency standard, including physical characteristics, block diagrams of the optical control CPT resonance system and of the digital control electronics is given. The characteristics of the frequency standard relative to general functionality and frequency stability are given, as measured on several units.

A reliability study has been conducted on capacitors made with 100 nm of silicon nitride, in an InP HEMT MMIC fabrication process. Special wafers were fabricated, containing 1482 200 /spl mu/m/spl times/200 /spl mu/m capacitors each, and these were probed automatically. They were subject to ramped-voltage stress and the breakdown voltages recorded. On a typical wafer the vast majority of the breakdown voltages are between 50 and 90 V. In addition, I-V curves were measured on a small number of specimens from 0 V up to breakdown. This was done in two regimes: above 25 V with a conventional setup, and below 25 V with an ultra-low-current measurement system. These were done at 25/spl deg/C and 175/spl deg/C above 25 V, and at 25/spl deg/C only below 25 V. These were fitted well with a model for the conductivity, consisting of an ohmic conduction at low voltages and Frenkel-Poole conduction at high voltages. Parameters of the fits included thermal activation energies, the voltage acceleration factor in the Frenkel-Poole model, and d/sub eff/, the effective thickness of the dielectric at the thinnest point. Analysis invoked the time-dependent dielectric breakdown model, which provides the time to failure as a function of the deff, while deff can be found from the ramped-voltage measurements. From the 10 wafers that have been probed so far, the mean of the distribution of failure times (at 1.5 V, 40/spl deg/C) is above 5/spl times/10/sup 7/ hrs, and the distribution becomes insignificant below 2/spl times/10/sup 6/ hrs. Further, the probability of failure in 10 years at 1.5 V, 40/spl deg/C is much less than 1 in 14,600. This indicates that 100 nm silicon nitride capacitors in this technology have good reliability.

The paper summarizes the relative advantages and disadvantages of coherent population trapping (CPT) or intensity optical pumping (IOP) for the implementation of a passive atomic frequency standard using the isotope /sup 87/Rb. This paper outlines the basic principles common to both CPT and IOP when using laser optical pumping, and makes explicit their similarities and their differences. This paper describes experimental results obtained in the same cell on the characteristics of the CPT and IOP /sup 87/Rb-hyperfine-resonance line. The measurements showed that the signal contrast is larger in CPT than in IOP for the same resulting line width; the light shift is smaller in CPT than in IOP, and is easier to control; in principle, a passive frequency standard based on CPT has a smaller size than that based on IOP, due to the absence of a microwave cavity. Conclusions on overall expectations for the future of such frequency standards are drawn.

This paper describes the performance, reliability, and applications of a new millimeterwave technology: the indium phosphide high electron mobility transistor (InP HEMT). This advanced technology is potentially an enabling technology for a wide range of millimeterwave systems.

The authors report on the state-of-the-art power performance of InP-based HEMTs (high electron mobility transistors) at 59 GHz. Using a 448- mu m-wide HEMT with a gate length of 0.15 mu m, an output power of 155 mW with a 4.9-dB gain and a power-added efficiency of 30.1% were obtained. By power-combining two of these HEMTs, an output power of 288 mW with 3.6-dB gain and a power-added efficiency of 20.4% were achieved. This is the highest output power reported with such a high efficiency for InP-based HEMTs, and is comparable to the best results reported for AlGaAs/InGaAs on GaAs pseudomorphic HEMTs at this frequency. >

We report robust GaN MMIC LNA operating over 4 GHz-6 GHz frequency range. An FET biased in common-drain configuration is used on the second stage of the MMIC to obtain good input return loss at the optimum noise match over the entire frequency range. The measured noise figure of the MMIC is less than 2 dB over the 4.5 GHz to 16 GHz frequency range and NF has a minimum of 1.45 dB at a frequency of 6.5 GHz. The MMIC gain is more than 10 dB and the input return loss of the MMIC is less than -10 dB over the 4 GHz-15 GHz frequency range. Reported MMIC can survive 5.4 W of incident RF power without front end protection. To the authors knowledge this is the best combination of the noise figure, input return loss, RF survivability and broadband response reported to date in this frequency range using GaN technology. The noise figure of the reported GaN MMIC is 0.5 dB lower than the overall noise figure of an equivalent GaAs pHEMT module consisting of the state of the art LNA and a 5 Watt power limiter at the front end.

We report development of a novel AlGaN/GaN/AlGaN double heterojunction field effect tansistor (DHFET) with improved device performance over the conventional single heterojunction GaN FET (SHFET). The GaN DHFETs with low Al content Al/sub 0.04/Ga/sub 0.96/N buffer layer exhibit three orders of magnitude lower subthreshold drain leakage current and almost three orders of magnitude higher buffer isolation than corresponding SHFET devices (600 M/spl Omega//sq. vs. 1 M/spl Omega//sq.). In GaN DHFET's with 0.15 /spl mu/m conventional T-gates we observed 30% improvement in saturated power density and 10% improvement in PAE at 10 GHz over a corresponding SHFET device.

A W-band DHBT power amplifier chip set consisting of a cascode power amplifier and a driver amplifier fabricated in InP technology is reported. The cascode power amplifier has a total of 160 um/sub 2/ of emitter area and results in a power gain of 8.5 dB and saturated output power of more than 14.4 dBm at 94.5 GHz. The driver power amplifier provides a peak signal gain of 9.8 dB at 102 GHz and peak saturated output power of 9.5 dBm at 94.7 GHz. To the author's knowledge, this is the highest reported output power and gain above 90 GHz for an HBT amplifier.

Coherent population trapping in alkali atoms has opened a new avenue in the implementation of atomic frequency standards having promising characteristics for field use. The paper gives a short description of the phenomenon, interprets experimental observations by means of a four-level model, outlines the use of such a phenomenon in the frequency standard field, and gives an evaluation of the achievable frequency stability based on the contrast and line Q realizable in practice.

Summary form only given. It has been pointed out by Henderson (1996) and others that HBTs are vulnerable to recombination-enhanced defect reactions (REDRs), which can lead to formation of crystal defects with activation energies (E/sub a/'s) as low as 0.35 eV. It is therefore possible that when conventional lifetests with junction temperatures from 200 to 300/spl deg/C are run, other high-E/sub a/ phenomena occur first, and the tests are subsequently stopped. This may have the result that the low-E/sub a/ phenomena are never observed. Thus these lifetests may fail to characterize the mechanism that will actually occur first at the low temperature of a typical application, and may therefore greatly overestimate the real reliability. Conventional lifetests have been run on the HRL Laboratories Generation 1 AlInAs/GaInAs HBTs, on InP substrates, with good results: the beryllium base dopant appears stable, there appear to be increases in the resistances of the emitter contacts, but there is no indication of increases in base currents, that would be a sign of defect generation. So in parallel with these tests, we have been running long-term lifetests at the very low junction temperatures of 125 and 160 C, in an attempt to detect low-Ea phenomena. This experiment was reported in detail when we were at about 14,000 hrs. But it has been continuing since then, and has now reached a power-on time of over 19,000 hrs (accumulated over an elapsed time of almost 3 years). We continue to see no failures, so we can now rule out low-E/sub a/ failures with a higher confidence level. To our knowledge, this is the only lifetest on HBTs of any composition, that has been run with temperatures well below 200 C.

Coherent population trapping is studied in ${}^{87}\mathrm{Rb}$ in a buffer gas. Experimental results are reported on the contrast of the field independent hyperfine resonance line and on its linewidth. A physical model, which includes an optical pumping process that traps atoms in a Zeeman sublevel of the ground state, is developed. The model explains the general behavior of the experimental observations.

Microwave VCO and system designers should be aware that attoFarad level changes in the dynamic performance of a varactor can correlate to changes in system settling response of fast hopping frequency synthesizers. It is theorized that a moisture/silicon interaction occurred within a packaged varactor diode due to imperfect wafer processing of the die and a flawed ceramic enclosure. The flawed ceramic allowed ambient moisture to penetrate and come in contact with exposed silicon at the surface of the die junction, causing an increase in interface (or surface) states which in turn increased the settling time constant of diode capacitance on the order of fifty microseconds. The increased time constant was correlated to an observed degradation in VCO phase settling. The increased phase transient was shown to recover with several time/temperature combinations in accordance with Arrhenius predictions.

This paper will summarize recent developments in the field of Si/SiGe HBT technology for high-speed communications applications. This technology promises to provide "III-V-like" performance in a silicon VLSI environment, and recent developments demonstrate that highly integrated mixed-signal devices can be implemented with outstanding performance and yield.

Significant advances in high-frequency, low noise amplifier (LNA) performance have been achieved. Noise figures under 2.0 dB have been demonstrated with several single-stage amplifiers incorporating devices from different wafers. These amplifiers utilized an Al/sub 0.48/In/sub 0.52/As-Ga/sub 0.47/In/sub 0.53/As lattice matched InP high-electron-mobility transistor device with a gate periphery of 50 mu m*0.2 mu m. The typical f/sub t/ of these devices is in excess of 120 GHz, with an extrinsic g/sub m/ of more than 900 mS/mm. The best result obtained for a single-stage LNA was 0.8 dB, with an associated gain of 8.7 dB at 63.5 GHz. A three-stage V-band amplifier produced a minimum noise figure of 2.6 dB, with 19.5 dB of gain at 61.0 GHz. >

Previous implementations of high-performance op amps in GaAs technology have been hindered by low transistor g/sub m/r/sub ds/, light sensitivity, and excessive backgating, which have limited gain and bandwidth. These limitations are overcome in the circuit reported here by the use of improved processing technologies and circuit design approaches. The GaAs MESFET depletion-mode n-channel technology employs 0.2- mu m e-beam defined gates, air-bridge interconnects for low capacitance, and molecular beam epitaxy (MBE) to grow the channel layers. The average threshold voltage of the resulting FETs is -0.6 V, and the extrinsic transconductance is approximately 500 mS/mm. H/sub 21/ measurements on individual devices yield an extrapolated f/sub T/ of approximately 8 GHz. The small-signal equivalent circuit model of a 50- mu m-wide device, derived from the measured S-parameters, is shown, and the resulting element values are presented. >

Low-temperature GaAs buffer technology was used to fabricate high-performance 0.2- mu m-gate-length, spike-doped GaAs MESFETs. A 400.0-nm low-temperature GaAs buffer was grown by molecular beam epitaxy (MBE) at a substrate temperature of 300 degrees C. The substrate temperature was raised to 580 degrees C for a brief in situ anneal and followed by the growth of the active spike-doped GaAs MESFET structure. The peak extrinsic transconductance, g/sub m/, was 600 mS/mm with an average pinch-off voltage, V/sub po/, of -0.6 V. An output conductance, g/sub o/, of 24 mS/mm resulted in a voltage gain of 25. The extrapolated f/sub T/ of the devices was 79 GHz. Static SCFL (source-coupled FET logic) frequency dividers fabricated in this technology exhibit a maximum clock rate of 22 GHz. Low-temperature AlInAs buffer growth has been applied to GaInAs/AlInAs HEMT (high-electron-mobility transistor) devices on InP. A 250.0-nm AlInAs buffer was grown at a substrate temperature of 150 degrees C, followed by an anneal under arsenic overpressure and a GaInAs/AlInAs superlattice prior to the HEMT structure, which is grown at T=510 degrees C. Devices fabricated with 0.2- mu m gates had g/sub m/ of 670 mS/mm and g/sub o/ of 2.55 mS/mm, giving a voltage gain of 250. >

A report is presented on the development of a planar low-temperature buffer AlInAs/GaInAs on InP high-electron-mobility transistor (HEMT) technology for use in digital and analog integrated circuits. This technology is attractive for circuit applications because of the high achievable f/sub T/ and f/sub max/, low output conductance and gate leakage current, and reduced susceptibility to backgating effects. Two alternative logic families-UFL and SCFL (source-couple FET logic)-were chosen for the realization of digital circuits. Measurements on the UFL ring oscillators exhibited a minimum gate delay of 13 ps with a power dissipation of 1.1 mW/gate at room temperature. The gate delay rose to 25 ps when the power dissipation increased to 3 mW/gate. This gate delay is expected to drop significantly with reductions in diode level-shift series resistance and improvements in transistor f/sub T/. The most complex SCFL circuit tested was a divide-by-eight counter. The SCFL circuits were configured as flip-flops in the divide-by-eight mode. The circuit operated at a maximum clock rate of 12.5 GHz. >

An approach to fabricating X-band power FETs by direct implantation into MBE-grown GaAs/Si incorporating low-temperature buffer layers is described. Devices fabricated on GaAs-on-Si wafers were compared directly to GaAs ion-implanted FET wafers that were processed in the same lot. The MBE low-temperature buffer layer was adapted to GaAs-on-Si to provide a high-resistivity layer to prevent Si out-diffusion from the Si substrate and to reduce strain in the GaAs layer. Excellent DC and RF device performance was obtained from both the GaAs/Si wafers and the GaAs/GaAs wafers. The wafers were put through a standard 0.5- mu m power FET production process. The sheet resistivity, the transconductance, the I/sub dss/ channel current, and the pinch-off voltages of the GaAs/Si devices were comparable to those of the GaAs/GaAs wafers. On-wafer DC and RF testing and mapping were performed to correlate material characteristics with device RF performance. The functional RF yield from on-wafer RF probing tests was very high for both GaAs/Si and GaAs/GaAs wafers, varying between 68 and 90% for GaAs/Si wafers and 94 and 97% for GaAs/GaAs wafers. Although the DC characteristics of the GaAs/Si wafers were comparable to those of the GaAs wafers, the RF characteristics were slightly worse, showing 2 dB less maximum available gain than the GAs/GaAs wafers. >

The scaling of the vertical dimensions of 0.15- mu m-gate-length Al/sub 0.48/In/sub 0.52/As-Ga/sub 0.47/In/sub 0.53/As high-electron-mobility transistors (HEMTs) to reduce their well-known excessive gate leakage current, premature breakdown voltage, and poor output conductance is discussed. It is found that, with a proper choice of doping densities and layer thicknesses, it is possible to realize very-high-performance AlInAs-GaInAs HEMTs (f/sub T/=160 GHz, f/sub max/=300 GHz for 0.15- mu m*50- mu m devices) with low gate leakage current, high breakdown voltage (7.0 V), and very low DC output conductance (45-mS/mm). The DC output conductance exhibits a very strong dependence on the AlInAs doping-thickness product and appears to be a limiting factor in the device power gain. By reducing the doping-thickness product, it was possible to reduce the output conductance by a factor of 3 and thus increase the power gain cutoff frequency by a factor of 1.7. >

Reports on the manufacturability of state-of-the-art passivated 0.1- mu m low-noise InP HEMTs (high electron mobility transistors). These HEMTs offer an attractive, cost-effective solution to millimeter-wave satellite communications. The authors discuss their yield and reproducibility, as well as typical performance at V- and W-bands. >

The authors report on the state-of-the-art power performance of InP-based HEMTs (high electron mobility transistors) at 59 GHz. Using a 448- mu m-wide HEMT with a gate-length of 0.15 mu m, an output power of 155 mW with a 4.9-dB gain and a power-added efficiency of 30.1% were obtained. By power-combining two of these HEMTs, an output power of 288 mW with 3.6-dB gain and a power-added efficiency of 20.4% were achieved. This is the highest output power reported with such a high efficiency for InP-based HEMTs, and is comparable to the best results reported for AlGaAs/InGaAs on GaAs pseudomorphic HEMTs at this frequency. >

The authors have conducted a systematic effort to improve the breakdown voltage of InP-based HEMTs without compromising their high frequency performance, and have demonstrated millimeter wave circuit results that are comparable to or exceed those of the best GaAs-based PHEMTs in the critical area of power-added efficiency and output power. This improvement was accomplished by a combination of developments in material growth and device design and fabrication. >

Frequency translation circuits are key elements in communication systems. This paper presents three different frequency multipliers and a frequency mixer designed using the InP HEMT technology. These successful first iteration MMICs are highlighted by a V-band frequency quadrupler that has 14.25 dB conversion gain with +3.25 dBm output power and a V-band mixer that has 10 dB conversion loss over a 12 GHz bandwidth.

A millimeter-wave MMIC low noise amplifier chip set has been developed. Based on the InP HEMT technology, these LNAs provide state-of-the-art performance as well as excellent yield and repeatability. With greater than 50% chip yield, a three-stage Q-band LNA design achieved 26 to 31 dB of gain from 42 to 50 GHz and 1.8 dB average noise figure from 43.3 to 45.7 GHz. In addition, there are six other LNA designs including a four-stage V-band LNA with 28 dB of gain and 2.3 dB noise figure and a two-stage balanced Q-band LNA that provided 17 dB of gain and has greater than 61% yield.

InP-based heterojunction bipolar transistors (HBT) an being actively developed For integrated circuit applications requiring high-speed performance. InP HBT is also a low-power technology with a turn-on voltage lower than that of the Si bipolar transistor. The material system is also compatible for optoelectronics integration. The ultimate usefulness of this technology, however, depends on its reliability for system applications. Our extensive experimental data indicates that the reliability performance of millimeterwave InP HBT's meets stringent system requirements such as flight specifications. Another InP-based technology, high-electron mobility transistors (HEMT) have, in the past five years, moved from the research laboratories to insertion in government and commercial electronic systems. For space payload applications of these two technologies we have projected mean-time-to-failures in excess of 10/sup 10/ hours at 45/spl deg/C operating temperature with corresponding activation energies of 1.6 to 1.9 eV. The failure rates are also vanishingly small with dispersions of 0.2 to 0.5 associated with the lognormal failure distribution. >

High electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) fabricated in the AlInAs-GaInAs epitaxial material system are described. The unique material and electronic properties of these ternary semiconductors provide extreme high frequency performance. Fundamental device designs for both the HEMT and HBT are presented with performance data. The implementation of these devices in small-scale circuits, ring oscillators, and dividers is demonstrated. >

Design, construction and performance of several cryogenically-coolable millimeter-wave amplifiers for radio astronomy applications, using AlInAs/GaInAs/InP HEMTs, are presented. The examples include a 40-50 GHz amplifier with an average noise temperature of about 15 K and a 60-80 GHz amplifier yielding a laboratory receiver noise temperature of 37 K at 60 GHz and 50 K at 75 GHz. >

A MMIC chip set for millimeter-wave (mmW) communication systems has been developed. The highlights are a 3-stage Q-band LNA with 2.0 dB NF/22 dB of gain and a 2-stage V-band LNA with 2.3 dB NF/15 dB of gain. Altogether, 7 MMIC chips (2 LNAs, 2 mixers, 2 downconverters, and 1 LO amplifier) make up this effort to develop low noise mmW building block functions in the InP HEMT technology. >

Accelerated lifetests have been conducted on AlInAs-GaInAs HBT devices on InP wafers. Current densities were relatively high, while junction temperatures were low enough (125 and 160/spl deg/C) to provide a check for low activation energy failures. 40 devices were tested, and about 14,000 hours have been accumulated so far. Changes similar to those found in conventional higher-temperature lifetests were observed, at times which are consistent with the activation energies of 1.1 to 1.5 eV determined in those tests. Otherwise, no significant changes were observed. Based on this, and some reasonable assumptions about acceleration factors, any failure mechanism with E/sub a/ down to 0.35 eV would not be expected to occur during use at 80/spl deg/C until a mean time of at least 2/spl times/10/sup 5/ hrs, which is more than a typical 15-year product life. Also, the rate for "freak" or "random" failures is found to be 344 FITs, with 95% confidence, again with reasonable assumptions about acceleration factors.

A single-stage 20-GHz power amplifier was developed using a double-doped AlInAs-GaInAs-on-InP HEMT. Output power of 516 mW (0.645 W/mm) with power-added efficiency of 47.1% and 7.1-dB gain were obtained from an 800- mu m-wide device. The device had a saturated output power of more than 560 mW (0.7 W/mm). This is believed to be the highest combination of output power, power density, gain, and power-added efficiency reported for an InP-based FET at this frequency. >

The first demonstration of GaN digital circuits is reported. First‐generation GaN digital technology has already shown high yields for circuits of considerable complexity. Specifically, a 31-stage ring oscillator was implemented using 217 transistors. Properties of the AlGaN/GaN material system that enable outstanding power handling capabilities of GaN heterojunction field effect transistors (HFETs), i.e. large bandgap, high breakdown field and high saturation velocity, also make it attractive for digital applications in harsh environments. Because of these unique material characteristics GaN digital control circuits have the potential to operate in high radiation environments, at elevated temperature, and directly from high voltage rails. Successful operation of GaN 31-stage ring oscillators at the highest base-plate temperature attainable by test setup of 265°C, indicates these circuits can operate at significantly higher temperatures.

GaAs has been grown by molecular‐beam epitaxy on both silicon and silicon on sapphire. The incorporation of a low temperature buffer has reduced the film stress from 3.0 to 2.2 kbar for GaAs grown on silicon. However, films stress can be completely removed for growth of GaAs with the incorporation of the low temperature buffer when grown on silicon on sapphire (SOS). The orientation dependence of GaAs grown on SOS has been investigated by growing on orientations slightly off axis from the (100) in the [011] direction by 2°, 4°, and 6°. X‐ray, mobility and photoluminescence measurements have been made, showing that growth on 6° misoriented SOS produces nearly stress free films, with materials properties similar to those of GaAs on silicon, and mobilities six times higher than those of GaAs grown on on‐axis (100) SOS. Metal–semiconductor field effect transistors (MESFETs) have been fabricated on GaAs on silicon showing device characteristics comparable to those of GaAs on GaAs.

Defect free strained layer epitaxy opens possibilities for further improvement on the quantum well two-dimensional electron gas FET (TEGFET) structures grown using the GaInAs/AlInAs on InP materials system. Increased freedom with composition allows for optimizing certain properties of the structure, such as, the conduction edge discontinuity which controls the maximum sheet concentration (ns); and the electron effective mass which influences the speed of the structure. These enhancements can be made respectively by increasing the Al concentration in the AlInAs and/or by decreasing the Ga concentration in the GaInAs. The maximum amount of strain which can be incorporated into the unrelaxed material sets an upper limit on the compositional tolerances. The tolerances will be shown to be large for the AlInAs and the active TEG GaInAs region. The compositions are obtained using the intensity oscillations observed in the reflection high energy electron diffraction (RHEED) specular beam during growth of GaAs, AlAs, and subsequently GaInAs on GaAs. X-ray rocking curves and photoluminescence (PL) are used to verify the calibrations for growths on InP. The dependency of the mobility on strain is shown. The maximum 300 K mobility obtained was 12,360 cm2/V·s with ns of 1.25×1012/cm2. The well thickness was 84 nm. The AlInAs and GaInAs were estimated to be +0.04 and +0.17 In fraction from lattice match respectively. A mobility of 11,550 cm2/V·s was obtained using a 34 nm well. Strong PL (10 K) peaks will be shown from the quantum well TEGFET structures having a full width at half maximum intensity as low as 12.5 meV. The energies are below the GaInAs bandgap energy ranging from 0.69 to 0.80 eV.

The status of lattice-matched high-electron-mobility transistors (HEMTs) and pseudomorphic AlInAs-GaInAs grown on In substrates is reviewed. The best lattice-matched devices with 0.1- mu m gate length had a transconductance g/sub m/=1080 mS/mm and a unity current gain cutoff frequency f/sub T/=178 GHz, whereas similar pseudomorphic HEMTs had g/sub m/=1160 mS/mm and f/sub T/=210 GHz. Single-stage V-band amplifiers demonstrated 1.3- and 1.5-dB noise figures and 9.5- and 8.0-dB associated gains for the lattice-matched and pseudomorphic HEMTs, respectively. The best performance achieved was a minimum noise figure of F/sub min/=0.8 dB with a small-signal gain of G/sub a/=8.7 dB. >

The Raman spectra of superionic conductors AgI and RbAg4I5 have been measured in both cation disordered and normal phases. Similarities in the observed spectra of these two materials are discussed. The frequency dependent conductivity is obtained from the spectra and compared to infrared results. Several possible interpretations of the observed spectra are considered.

This paper compares Inconel 625, titanium 6242S, and 316 stainless steel as candidate plasma chamber first wall structural materials. Factors which have a significant effect on plasma chamber design are identified. Results are based on studies conducted for the Power Generating Fusion Reactor (PGFR) having a peak plasma power of 650 MW. The analyses use unirradiated material properties. Properties important in the design are discussed. The effect of material properties and load conditions on life of the plasma chamber is also addressed.

The Raman spectrum of a superionic conductor, α-AgI, is compared with the spectra of the melt of AgC l and AgBr, in order to determine the responsible Raman processes. We conclude that because of the strong anharmonicity and high translational disorder in superionic conductors, spectra analyses based on the concept of harmonic lattice are unsuitable. A dynamical picture of ions similar to that of liquids appears to be more useful than the phonon concepts.

The quality of GaInAs‐AlInAs epitaxial layers is found to be critically dependent on the degree of (100)‐InP substrate misorientation. The alloy quality of both materials is improved when the substrate is misoriented 4° off the (100). The heterojunction interface quality as determined by the full width at half‐maximum of quantum‐well photoluminescence is also improved when a substrate misoriented by 4° is used. A degradation of both alloy and interface quality as compared to material on (100) InP is observed when the misorientation is 2°. These effects are also observed for strained quantum‐well structures.

A wide-bandwidth GaAs MESFET operational amplifier is reported, with a 65-dB DC gain and a 20-GHz gain-bandwidth product at 500 MHz. The circuit uses a variety of local feedback techniques to enhance the overall gain. The use of an undoped GaAs buffer, grown at a relatively low temperature ( approximately=300 degrees C), eliminates backgating and light sensitivity. The circuit was fabricated in an 80-GHz f/sub T/ MESFET process, with 0.2- mu m electron-beam defined gates. The high levels of 1/f noise, MESFET frequency-dependent output conductance, and large offset voltage standard deviation limit the application of the circuit to moderate precision applications. >

Investigations of the distributions of two acid dyes within a dyed polyamide 6 substrate have been performed using the rolled-film method. The diffusion coefficients of the dyes increased with increase in the dye concentration in the dyebath and in the polymer. The more hydrophobic dye exhibited anomalous behavior which has been attributed to diffusion of small dye aggregates. Diffusion behavior of this dye in the presence of a nonionic surfactant has been explained in terms of the interaction equilibria between dye and surfactant species in solution.

The fabrication of high-performance digital integrated circuits with low-temperature buffer (LTB) GaAs MESFET technology is presented. Individual 0.2- mu m-gate-length transistors show a g/sub m/ of 600 mS/mm and an extrapolated f/sub T/ of 80 GHz. Backgating and light sensitivity are eliminated with the LTB technology. Static source-coupled FET logic frequency dividers exhibit a maximum clock rate of 22 GHz. >

Low-temperature AlInAs buffer layers incorporated in AlInAs-GaInAs HEMT epitaxial layers grown by MBE are discussed. A growth temperature of 150 degrees C followed by a short anneal is shown to eliminate kinks in the device I-V characteristic and sidegating and to reduce the output conductance dramatically. >

The performance of long (1.3- mu m) and short (0.3- mu m) gate-length Al/sub 0.48/In/sub 0.52/ As-Ga/sub 0.47/In/sub 0.53/ high-electron-mobility transistors (HEMTs) is reported. Transconductances of 465 and 650 mS/mm, respectively, were achieved. The 0.3- mu m-long gate-length device exhibited an f/sub t/>80 GHz. These results are attributed to the excellent electronic properties of the AlInAs-GaInAs modulation-doped system. >

The millimeter-wave performance is reported for Al/sub 0.48/In/sub 0.52/As-Ga/sub 0.47/In/sub 0.53/As high-electron-mobility transistors (HEMTs) with 0.2- mu m and 0.1- mu m-long gates on material grown by molecular-beam epitaxy on semi-insulating InP substrates. Devices of 50- mu m width exhibited extrinsic transconductances of 800 and 1080 mS/mm, respectively. External f/sub T/ (maximum frequency of oscillation) of 120 and 135 GHz, respectively, were measured. A maximum f/sub T/ of 170 GHz was obtained from a 0.1*200- mu m/sup 2/ device. A minimum noise figure of 0.8 dB and associated gain of 8.7 dB were obtained from a single-stage amplifier at frequencies near 63 GHz. >

A dual, phased array ZnO transducer has been developed for wideband acousto-optic Bragg cell operation. The two-phased array transducers a re mounted adjacently on the beveled face of a LiNbOg delay line in such a manner that the a coustic beams are colinear and in phase at the transfer frequency. A low loss diplexer is employed to split the input signal and eliminate i nterference between the two transducers. The angular steering of the dual lobe acoustic beam with frequency from the phased array transducer is employed to track the Bragg angle and minimize momentum mismatch loss. A bandwidth of Af = 1.3 GHz is obtained operating in the f requency range from 1.3-2.6 GHz. The dual transducer configuration was chosen to opt-mize the Bragg cell efficiency. Operating at 8300 8, a 5 percent p er RF watt diffraction efficiency is projected.

This paper describe the design, fabrication, and testing of high-speed GaAs static divider circuits that operate up to 17.9 GHz at room temperature. The dividers were implemented in both buffered FET logic (BFL) and capacitively enhanced logic (CEL), and were fabricated with 0.2 µm gate length MESFETs, active channels grown with molecular beam epitaxy (MBE), and airbridge interconnects.

High-performance digital integrated circuits have been fabricated with low-temperature buffer GaAs MESFET technology. The materials structure eliminates side-gating and light sensitivity, and improves FET performance. Individual transistors with a 0.2-mm gate length have a transconductance g m of 600 mS/mm and an extrapolated cutoff frequency f T of 80 GHz. Static SCFL frequency dividers fabricated in this technology exhibit a maximum clock rate of 22 GHz

The Raman spectrum of a superionic conductor, α-AgI, is compared with the spectra of the melt of AgC£ and AgBr, in order to determine the responsible Raman processes. We conclude that because of the strong anharmonicity and high translational disorder in superionic conductors, spectra analyses based on the concept of harmonic lattice are unsuitable. A dynamical picture of ions similar to that of liquids appears to be more useful than the phonon concepts.