Balanced subharmonic mixers for retrodirective-array applications

The drawback of conventional Pon retrodirective antenna systems is the requirement of a local oscillator (LO) working at approximately twice the receive frequency. This limits the use of these systems to rather moderate frequencies where such an oscillator can be obtained. To overcome this problem, a new phase conjugate mixer topology is proposed, whereby the use of a harmonic mixer instead of the conventional fundamental type effectively halves the LO frequency requirement. Another significant problem of conventional Pon phase conjugate mixers is the small spacing in frequency, typically only a few 0.1% of the carrier frequency, between RF, IF, and LO frequency. In this paper, we have overcome this problem by introducing a double balanced structure with a novel phasing strategy. The phasing circuit automatically cancels the RF and LO signal at the system's output port, giving 36-dB RF/IF, and 34-dB LO/IF isolation for a 970-MHz IF and 990-MHz RF signal. The new mixer structure proposed here is an attractive proposition for use in retrodirective antenna arrays significantly enhancing their potential for application in the millimeter-wave frequency range     

Assessment of the resistance to diffusion destruction of AlAs/GaAs nanoscale resonant-tunneling heterostructures by IR spectral ellipsometry

A technique for assessing the quality of AlAs/GaAs nanoscale resonant-tunneling heterostructures from the viewpoint of their resistance to diffusion destruction is developed. The diffusive spreading of AlAs/GaAs heterostructure layers is revealed by infrared (IR) spectral ellipsometry and the Al and Si diffusion coefficients in GaAs are determined.     

Shot noise of a high-speed resonance-tunneling diode based on the GaAs/AlAs heterosystem

A method for the measurement of the shot noise of semiconductor diodes at low temperatures and frequencies of no less than 100 MHz is proposed. The technique is based on the Y-factor method that is modified for the measurement in which the device under study is not matched with the measurement circuit. The shot noise of high-speed resonance-tunneling diodes (RTDs) based on the GaAs/AlAs heterosystem is analyzed. It is demonstrated that an increase in the bias voltage leads to an increase in the Fano factor from about 0.5 at low bias to values of greater than unity in the range of the negative differential conductance of the RTD. When the bias voltage further increases, the Fano factor decreases and becomes close to 0.5. At all of the temperatures and bias voltages, a reliable decrease in the Fano factor to a level of less than 0.5 is not observed. We assume the sequential rather than coherent electron transport for the RTD based on the GaAs/AlAs heterosystem.     

AlAs/GaAs Schottky-collector resonant-tunnel-diodes

The Schottky-collector resonant-tunnel-diode (SRTD) is an resonant-tunnel-diode with the normal N⁺ collector layer and ohmic contact replaced by direct Schottky contact to the space-charge layer, thereby eliminating the associated parasitic series resistance Rins. By scaling the Schottky collector contact to submicron dimensions, the device periphery-to-area ratio is increased, decreasing the periphery-dependent components of the parasitic resistance, and substantially increasing the device's maximum frequency of oscillation. We report measured d.c. and microwave parameters of planar SRTDs fabricated with 1 μm-geometries in AlAs/GaAs.     

新型四次谐波混频电路

本文介绍了一种适用于高次谐波混频的电路原理图,基于空闲频率相位抵消理论,该混频电路结构可以避免复杂的空闲频率回收电路设计,同时能获得很高的端口隔离度。基于该结构,设计了新型的Ka波段四次谐波混频器,该混频器在38.4 GHz测得最小变频损耗 8.3 dB,在34-39 GHz 变频损耗小于10.3dB, LO-IF、RF-LO、 RF-IF 端口隔离度分别优于30.7 dB、 22.9dB、46.5dB。     

Low conversion-loss fourth subharmonic mixers incorporating CMRC for millimeter-wave applications

Low conversion-loss millimeter-wave fourth subharmonic (SH) mixer designs are proposed in this paper. A millimeter-wave (35 GHz) fourth SH mixer with four open/shorted stubs is designed and measured. The conversion loss is less than 15 dB within a 2.4-GHz bandwidth. The minimum loss is 11.5 dB at the center frequency. By replacing two of the shunt stubs with a dual-frequency in-line stub consisting of newly developed compact microstrip resonating cells (CMRCs), the performance of the SH mixer is improved significantly. At 35 GHz, the conversion loss of this new fourth SH mixer is as low as 6.1 dB with a 3-dB bandwidth of 6 GHz. The conversion loss in the whole Ka-band (26.5-40 GHz) is less than 16 dB. The proposed fourth SH mixer incorporating with CMRCs provides a low-cost high-performance solution for RF subsystem design.     

基于平面肖特基二极管的毫米波固定调节式谐波混频器

基于GaAs肖特基势垒二极管,研制出了两个不同波段的谐波混频器。在场仿真软件中,二极管的非线性结采用lumped端口来模拟,通过场分析方法分析二极管各端口的阻抗。谐波混频电路被分成不同部分来单独优化设计,基于优化设计的各独立电路,建立谐波混频器的整体场仿真模型,通过提取相应的S参数文件分析混频器的变频损耗。150GHz 谐波混频器测得最低变频损耗10.7dB,在135-165GHz变频损耗典型值为12.5dB。180GHz 谐波混频器测得最低变频损耗5.8dB,在165-200GHz变频损耗典型值为13.5dB,在210-240GHz变频损耗典型值为11.5dB。     

Transient switching behavior of the resonant-tunneling diode

A quantum mechanical analysis is used to treat the transient behavior of the resonant-tunneling diode (RTD). The use of the Wigner formalism permits inclusion of the quantum mechanics inherent in the device, while offering a Boltzmann-like equation that is rather easily implemented. Self-consistent treatment of the potential introduces plasma oscillations in the distribution, which leads to the oscillatory current transient. Fourier analysis of this transient indicates that the RTD behaves inductively at frequencies under 2 THz, consistent with the ballistic nature of the carriers. At higher frequencies, the dominant mechanism is the capacitive charging and discharging of the quantum well, which leads to capacitive behavior of the device. The real part of the conductance is negative for frequencies under 1.5 THz, and positive for higher frequencies. The critical frequencies are shown to be independent of the relaxation time used to model dissipation, although the magnitude of the conductance decreases as the dissipation increases     

P—type AlAs／[GaAs／AlAs]Semiconductor／Superlattice DBR Grown by MBE

A p-type AlAs(70.2 nm)/16.5 period [GaAs(3 nm)/AlAs(0.7 nm)] semiconductor/superlatice distributed Bragg reflector (DBR) has been grown on n +-GaAs(100) substrate by V80H molecular beam epitaxy system. Experimental reflection spectrum shows that its central wavelength is 820 nm, with the peak reflectivity for 10-pair DBR of as high as 96 %, and the reflection bandwidth of as wide as 90 nm. We formed a 20×20 μm 2 square mesa to measure the series resistance using wet chemical etching. From the measurement result, the series resistance of about 50 Ω is obtained at a moderate doping (3×10 18 cm -3 ). Finally, the dependence of the resistance of the DBR on the temperature is analyzed. From the experimental result, it is found that the mechanism of the low series resistance of this kind of DBR may increase the tunneling current in the semiconductor/superlattice mirror structure, which will result in a decrease in series resistance.     

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.     

Wet Oxidation in a Square Sandwich Composite of GaAs/AlAs/GaAs

Wet oxidation in a square sandwich composite, GaAs/AlAs/GaAs, with varying thickness of the AlAs layer was investigated in a temperature range of 400°C–480°C. At a given temperature and time, the oxidation depth increases with increasing thickness of the AlAs layer. A model based on the boundary layer diffusion in a sandwich composite is used to interpret the thickness effect, and the theoretical predictions are in good agreement with the measured oxidation data. The theory also predicts a value of 0.53 eV ± 0.03 eV to be the difference in activation energies of water vapor diffusion in the central layer AlAs and the outer layers GaAs in the temperature range studied. Such a difference remains to be verified experimentally.     

Negative differential conductance in GaAs/AlAs superlattices

Negative differential conductance has been characterised on a series of n-doped GaAs/AlAs superlattices due to Esaki's negative effective mass mechanism. High electron peak velocities (up to 10/sup 7/ cm/s) were obtained together with high current densities (up to 150 kA/cm/sup 2/). These preliminary results are promising for microwave applications.<>     

Experimental study of microwave reflection gain of AlAs/GaAs/AlAs quantum well structures

Reports on microwave reflection gain measurements on single quantum well AlAs/GaAs/AlAs resonant tunnelling structures. Reflection gain against frequency measurements in the 0.050-26.5 GHz range were performed. The equivalent negative high-frequency resistance and capacitance as a function of frequency were determined for a diode of area 49 mu m/sup 2/. The point at which the reflection gain exceeds unity (0 dB) is noted to be the onset of possible oscillations, and thus yields a negative resistance.<>     

A combined model of a resonant-tunneling diode

A combined model of a resonant-tunneling diode is suggested. This model is based on the semiclassical and quantum-mechanical (the wave-function formalism) approaches. In addition to certain factors, important properties of the device heteroboundaries, in particular, the shape of the energy-band offset and the surface charge, are taken into account in the model. It is shown that the model can be used to obtain satisfactory agreement with experimental data when calculating the current-voltage characteristics of the diode. It is important that the peak voltages are determined with a good accuracy only if the resistances of extended passive regions and the surface charge of the heteroboundaries are taken into account.     

GaAs/Si/AlAs异质结的DLTS实验研究

利用深能级瞬态谱(DLTS)技术研究了Si夹层和GaAs层不同生长温度对GaAs/AlAs异质结晶体品质的影响.发现Si夹层的引入并没有引起明显深能级缺陷,而不同温度下生长的GaAs/Si/AlAs异质结随着温度的降低,深能级缺陷明显增加,并进行了分析,得到深能级是由Ga空位引起的,在600℃时生长的晶体质量最佳.     

A monolithic integrated schottky diode for microwave mixers

A new type of planar microwave mixer diode was produced on GaAs by a self-aligned process, resulting in high precision and yield. Up to now only planar diodes made by the highly sophisticated process of double selective epitaxy met the requirements of mixer operation at X-band. The new design requires only one epitaxial layer. It takes advantage of the inherent doping profile of the epitaxial layer instead of using two different layers. Microwave measurements showed that parasitic elements in the equivalent circuit can be neglected. This is due to the monolithic integration of the diode into a microstrip line which makes packaging superfluous. A cutoff frequency of 220 GHz was achieved.     

Ka-band monolithic GaAs balanced mixers

Monolithic integrated circuits have been developed on semi-insulating GaAs substrates for millimeter-wave balanced mixers. The GaAs chip is used as a suspended stripline in a cross-bar mixer circuit. A double sideband noise figure of 4.5 dB has been achieved with a monolithic GaAs balanced mixer filter chip over a 30- to 32-GHz frequency range. A monolithic GaAs balanced mixer chip has also been optimized and combined with a hybrid MIC IF preamplifier in a planar package with significant improvement in RF bandwidth and reduction in chip size. A double sideband noise figure of less than 6 dB has been achieved over a 31- to 39-GHz frequency range with a GaAs chip size of only 0.5 × 0.43 in. This includes the contribution of a 1.5-dB noise figure due to IF preamplifier (5-500 MHz).     

Self-passivated GaAs/W mixer diode

GaAs/tungsten Schottky barrier mixer diodes have been fabricated in a self-passivated, grown guard layer configuration. These devices have exhibited 0.64 eV barrier voltages together with the ability to withstand nanosecond RF pulses in excess of 8 ergs with no resulting deterioration in noise figure performance. Such high burnout resistance properties are attributed to the absence of any significant metallurgical interaction between the GaAs and tungsten at temperatures as high as 600°C. The somewhat high noise figures exhibited by these devices are attributed to interface states, possibly arising from strain.     

GaAs/AlAs超晶格中的TO声子限制模

本文报道在室温和非共振散射条件下,GaAs/AlAs 超晶格结构中TO声子限制模的拉曼散射测量结果.超晶格样品用MBE方法生长在<001>晶向的GaAs衬底上.在背散射条件下,具有E对称性的TO 声子是拉曼禁戒的.但是利用近布儒斯特角入射和大孔径的散射光收集透镜,我们观测到分别限制在GaAs和AlAs层中的TO声子模.其中,限制在AlAs层中的TO模是首次报道.从测量的TO声子限制模频率得到的声子色散曲线与GaAs和AlAs体材料的TO声子色散曲线进行比较,二者符合良好.进一步证明,超晶格结构的拉曼散射测量是测定晶体声子色散曲线的有效的实验方法.