Investigation of GaAs Schottky barrier diodes in the THz range

The properties of GaAs Schottky barrier diodes as video detectors and mixing elements were investigated in the frequency range from 0.8–2.5 THz. For the most sensitive diode, the video responsivity and system noise temperature were measured as a function of incident laser power. The highest video responsivity was 2,000 V/W at 214μm and 60 V/W at 118μm. For five diodes differing in doping, capacitance, series resistance and anode diameter, the system noise temperature was measured at 214μm and 118μm. The best single sideband (SSB) values are 12,300 K and 24,200 K at 214μm and 118μm, respectively. The system noise temperature versus frequency is given over the range from 0.5–3 THz for two specific diodes demonstrating that the sharpness of the I–V characteristics is only of secondary importance for mixer perfomance at such high frequencies.     

Reliability and micro-structural properties of GaAs Schottky diodes for submillimeter-wave applications

Whisker contacted GaAs Schottky barrier diodes are the standard devices for mixing and multiplier applications in the THz frequency range. This is mainly due to their minimum parasitics and mature technology. But with the decreasing size of the anode contact, which is required for operation at high frequencies (up to approx. 3 THz), the reliability and the micro-structural understanding of the Schottky barrier becomes increasingly important. This contribution presents new results concerning the reliability of Schottky diodes and the physical properties of small-area Schottky junctions, especially at low current densities. For these purposes a number of different Schottky diodes have been fabricated with different epilayer doping concentrations and anode diameters. Measured I/V characteristics show that the diode current deviates considerably from the ideal thermionic current behavior with decreasing diode diameter. This deviation shows an exponential dependence on the diode voltage and is a function of the doping concentration of the active layer. For a given doping concentration in the epi-layer and decreasing anode diameter, this phenomenon shifts the minimum of the ideality factor towards higher current densities. An explanation is given in terms of a difference of the cyrstallinity of the polycrystalline platinum films on the GaAs for decreasing SiO₂ aperture size in connection with a reduced Pt mobility in the electrolyte. The reliability of Schottky barrier diodes under thermal and electrical stress has been investigated on different THz Schottky diode structures. The results show that the barrier height and the ideality factor of the fabricated structures are not affected by thermal stress. Electrical stress induced by large forward currents up to a current density of 10 kA/mm² even leads to a slight increase of the barrier height and a reduction of the series resistance.     

Harmonic mixing and detection with Schottky diodes up to the 5 THz range

We report results of harmonic mixing experiments between a 0.4 THz oscillator and FIR lasers at 4.2 and 5.3 THz using μ-size Schottky barrier diodes, together with rectification results in the range of 0.6-5.3 THz for different diodes and coupling methods.     

GaAs Schottky diodes with near-ideal characteristics

The I-V characteristics of some GaAs Schottky-barrier IMPATT diodes are found to be nearly ideal at operating temperatures (∼200°C). Fabricated on epitaxial n-type substrate with platinum contacts, the diodes use a truncated cone shape to avoid soft breakdown. The breakdown voltage and its temperature dependence are close to calculated values for one-sided abrupt junctions.     

Barrier height engineering on GaAs THz Schottky diodes by means ofhigh-low doping, InGaAs- and InGaP-layers

Barrier height engineering of n-GaAs-based millimeter-wave Schottky diodes using strained InGaAs/GaAs and InGaP/GaAs heterostructures and a high doping surface layer is presented. The Schottky barrier height can be varied between Φ_fb=0.52 eV and Φ_fb=1.0 eV. The use of a pseudomorphic InGaAs layer and/or a thin high doping layer at the surface significantly reduces the Schottky barrier height. This is advantageous for low-drive zero bias mixing applications, A full quantum mechanical numerical calculation is presented to simulate the influence of different high doping layer thicknesses on the diode's dc characteristic. The theoretical results are compared with experimental results, For reverse bias applications (e.g., varactors) a barrier height and breakdown voltage enhancement is realized with a lattice matched InGaP/GaAs heterostructure. The barrier height value is determined by temperature dependent dc-measurements. The epitaxial layered structures are grown by molecular beam epitaxy. The diode devices are fabricated in a fully planar technology using selective oxygen implantation for lateral isolation. The diode's cut-off frequencies are in the THz-range     

High reliability sputtered Schottky diodes on GaAs

We describe developments to improve reliability and power handling for high frequency applications in whisker-contacted Schottky barrier diode mixers, detectors and multipliers fabricated using sputtered refractory metals and silicides. The lift-off process has been used to fabricate diodes on GaAs with ideality factors of 1.18 and 1.06 for W/GaAs and TiSi_x/GaAs contacts respectively.     

Electrical characteristics of GaAs MIS Schottky diodes

The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of GaAs metal-insulator-semiconductor (MIS) Schottky barrier diodes are investigated over a wide temperature range and compared with MS diodes. The effects of the insulating layer on barrier height and carrier transport are delineated by an activation energy analysis. Excess currents observed at low forward and reverse bias have also been analyzed and their cause identified. A capacitance anomaly consistently noticed in MIS Schottky barriers is resolved by stipulating a non-uniform interfacial layer, and a self-consistent model of the GaAs MIS Schottky barrier is developed by analyzing I-V and C-V data of both MIS and MS diodes.     

Fabrication and analysis of GaAs Schottky barrier diodes fabricated on thin membranes for terahertz applications

The GaAs Schottky diode is predominantly used as the critical mixer element in heterodyne receivers in the frequency range from 300 GHz to several THz[1]. At operating frequencies above one THz the skin effect adds significant parasitic resistance to the diode which degrades the receiver sensitivity. A novel diode structure called the Schottky barrier membrane diode is proposed to decrease the skin effect resistance by reducing the current path between the Schottky and ohmic contacts. This is accomplished by fabricating the diode on a very thin membrane of GaAs (about 1 μm thickness). A theoretical analysis has shown that this will reduce the substrate resistance by 60% at 3 THz. This reduction in resistance corresponds to a better frequency response which will improve the device's performance as a mixer element.     

Numerical analysis of GaAs epitaxial-layer Schottky diodes

A computer simulation of GaAs epitaxial-layer Schottky-barrier diodes has been carried out. The present work extends previous drift-diffusion equation (DDE) Schottky-barrier diode simulations to very thin epilayers of GaAs as well as to higher forward bias voltages. Diodes having epitaxial layers of 0.12 and 1.0 µm were modeled with an emphasis on comparison with experiment. To achieve better agreement with experimental data an interfacial layer was included in the model, resulting in a voltage-dependent barrier height. The bias voltage at which the I-V characteristic becomes strongly nonideal is predicted to depend more on the potential drop across the interfacial layer than on the series resistances present in the devices studied. The separate contributions of the dynamic resistance of the junction and of the series resistances of the epitaxial and bulk regions to the total resistance were examined for forward biases up to 1.1 V.     

Traps in fast-neutron irradiated GaAs Schottky diodes

GaAs Schottky diodes were irradiated with an essentially gamma-free beam of 5 MeV neutrons and the resultant trap (and defect) structure analyzed. The trap structure is shown to consist of energetically discrete levels, but the levels are found not to operate independently. A new defect model is proposed based on coupled-trap levels and is shown to be in good agreement with the observations. On the basis of this model, the following values for discrete trap levels were determined: 175, 220, 325, 380 and 460 mV below the construction band.     

Design and fabrication of 0.5 micron GaAs Schottky barrier diodes for low-noise terahertz receiver applications

Recent technological advances have made possible the development of heterodyne receivers with high sensitivity and high spectral resolution for frequencies in the range 1,000–3,000 GHz (1–3 THz). These receivers rely on GaAs Schottky barrier mixer diodes to translate the high-frequency signal to a lower frequency where amplification and signal processing are possible. At these frequencies, the diode quality is a major limitation to the performance of the receiver. The design, fabrication and DC evaluation of a diode for this frequency range is presented. A figure-of-merit cut-off frequency of over 10 THz is achieved with a record low zero biased capacitance of 0.5 fF. Results from RF tests are also given.     

Local-oscillator-induced noise in GaAs Schottky mixer diodes

Increased noise temperature induced by local-oscillator power has been measured in Schottky-diode millimetre-wave mixers at 250 MHz and 4.75 GHz. Electric-field calculations indicate a portion of this noise is due to intervalley scattering in the undepleted epitaxial layer directly adjacent to the Schottky-diode anode. A noise-temperature equation is presented, which accounts for both shot and thermal noise, where the thermal portion includes the intervalley scaltering component.     

Schottky diodes for analogue phase shifters in GaAs MMICs

A simple Schottky diode structure, which is easily implemented in a foundry gallium arsenide (GaAs) process, is described. This structure occupies very much less area than the usual technique of realising Schottky diodes, using standard FET structures. Two variations of the diode have been characterized and modeled using a standard equivalent circuit. This has been used to design a simple analogue phase shifter based on a loaded-line configuration. The phase shifter was manufactured using a standard foundry process and has shown excellent results in terms of phase shift linearity with tuning voltage, combined with low insertion loss, over the range 2-8 GHz     

面向太赫兹应用的InP基肖特基二极管

Based on characteristics such as low barrier and high electron mobility of lattice matched In_0.53Ga_0.47 As layer,InP-based Schottky barrier diodes（SBDs） exhibit the superiorities in achieving a lower turn-on voltage and series resistance in comparison with GaAs ones.Planar InP-based SBDs have been developed in this paper.Measurements show that a low forward turn-on voltage of less than 0.2 V and a cutoff frequency of up to 3.4 THz have been achieved.The key factors of the diode such as series resistance and the zero-biased junction capacitance are measured to be 3.32Ωand 9.1 fF,respectively.They are highly consistent with the calculated values.The performances of the InP-based SBDs in this work,such as low noise and low loss,are promising for applications in the terahertz mixer,multiplier and detector circuits.     

Utilisation de diodes Schottky comme détecteurs et mélangeurs à 30 THz (Using a Schottky diode in detecting and mixing at 30 THz)

La note décrit les résultats préliminaires obtenus avec des diodes Schottky utilisées comme mélangeuses dans la région des 10.6 ?m. Le battement entre deux lasers à CO2 a été observé ainsi que des effets de directivité et l'influence de la polarisation de la diode. à 10.6 ?m une sensibilité de la détection de 1 V/W a été obtenue. The letter describes preliminary results on Schottky diode mixers at 10.6 ?m. We observed the beat note between two CO2 radiation lasers. The detection dependence is reported with respect to the directivity and the d.c.bias. A sensitivity of 1 V/W was obtained at 10.6 ?m.     

A behavioral circuit simulation model for high-power GaAs Schottky diodes

This paper proposes a physically based behavioral circuit simulation model for high-power GaAs Schottky diodes which is valid over all regions of operation. No conditional statements are needed to define the regions of operation. A new and more accurate method of obtaining depletion capacitance model parameters from the measured capacitance values is proposed. A simple current- and temperature-dependent resistance model is used to model the nonlinear diode resistance as well as contact and packaging resistances. The validity of the model is demonstrated under various DC and transient switching conditions. Simulation results are compared with the experimental data obtained from a 200 V GaAs Schottky diode. The diode model is tested at various temperatures in different test circuits and the simulation results are shown to be in excellent agreement with the measured data under static and dynamic switching conditions. The model can be easily implemented in other circuit simulators.<>     

Computer study on GaAs Schottky barrier IMPATT diodes

Oscillation characteristics of GaAs Schottky barrier IMPATT diodes are studied by computer simulation. For a Schottky barrier-n-n⁺ structure, the Read condition and the just-punch-through condition are found to be optimum with respect to the efficiency and power at 30 GHz. In order to improve the efficiency, a superabrupt doping profile is proposed and a high efficiency of 32 per cent is predicted. Calculation of the frequency dependence of the efficiency shows that GaAs IMPATT diodes still have the potentiality of high efficiency oscillator at 100 GHz and they are a promising microwave source in mm-wave region.     

4H-silicon carbide Schottky barrier diodes for microwave applications

In this paper, physical models for vertical 4H-silicon carbide (4H-SiC) Schottky diodes are used to develop a design method, where a maximum cutoff frequency for a given punch-through is achieved. The models presented are also used to extract microwave simulator computer-aided design (CAD) models for the devices. A device process was developed and Schottky diodes were fabricated in-house. Characterization of the devices was performed and compared to the theoretical models with good agreement. A demonstrator singly balanced diode mixer was simulated using the developed models. The mixer was fabricated using the in-house developed diodes, and measurements on the mixer show good agreement with the CAD simulations. A conversion loss of 5.2 dB was achieved at 850 MHz, and an excellent IIP/sub 3/ of 31 dBm at 850-MHz RF was measured, at 30-dBm P/sub LO/. These results verify the enhanced properties of the SiC Schottky diode compared to other nonwide bandgap diodes.     

T形阳极太赫兹GaAs肖特基二极管的设计与制备

通过对平面形太赫兹肖特基二极管的结构与寄生参数的分析优化,设计并研制了适用于太赫兹频段的不同阳极直径的管芯。管芯为小尺寸设计,采用双层胶电子束直写技术制作T形阳极,阳极剥离后采用100nm的SiO_2介质进行钝化保护,比传统工艺约500nm的SiO_2介质大幅降低,有效降低了器件寄生电容,研制出截止频率f_T(C_(j0))8THz、f_T(C_(total))3.9THz的管芯。通过直流I-V测试和小信号S参数测试提取管芯参数,并分析对比了不同阳极直径管芯的性能参数。