Numerical Simulation of the Base Impedance of Long Wire Whisker Antennas

With increasing frequencies the whisker structures used to contact honeycomb Schottky diodes remain no longer thin compared to wavelength. Whereas the finite thickness and the detailed tip shape do not influence the antenna pattern very much the antenna base impedance depends on these parameters to a great extent. A good impedance matching between Schottky diode and whisker antenna is necessary to optimise mixer or detector performance and can only be achieved if the antenna impedance is known. Antenna base impedances have been simulated numerically and checked by means of scaled model measurements for several whisker shapes. The influence of further parts of the antenna environment, as for example reflectors, has also been investigated. Simulation results have been discussed and compared to theory. Simulation has been found out to be a reliable tool for the determination of base impedances of almost arbitrarily shaped whisker antennas.     

Bipolar-mode Schottky contact and applications to high-speed diodes

A Schottky contact operation combined with minority-carrier transport, a concept of bipolar-mode Schottky contacts, is proposed. There are two bipolar-mode Schottky contacts. One acts as a minority-carrier injector causing conductivity modulation without excessive carrier accumulation, while the other operates as an ideal ohmic contact to conduct minority carriers without accumulation. Applicationally, these contacts are utilized to improve conventional Schottky diodes and p-n diodes, respectively and a high-voltage Schottky diode (BSBD) and a fast-recovery p-n diode (quasi-LLD) can then be realized.     

Improvement of responsivity of high-speed infrared detector using hot carriers in semiconductors

A room temperature, high-speed and high-sensitive infrared hot carrier detector using p-type Ge has been investigated at 10.6 μm. The detector is composed of a whisker antenna and a diode contact forming an ohmic contact on p-type Ge. This detector has the merit that one can easily have impedance matching between the antenna and the diode contact without any matching section, so that high sensitivity can be obtained. A voltage sensitivity 16 dB higher than that of metal-insulator-metal (MIM) point contact diode has been observed from this detector.     

The performance of Schottky diodes as far-infrared modulators

We analyze the performance as a terahertz-frequency modulator of a small-area Schottky diode mounted in a corner-cube antenna. The analysis includes the effects of carrier inertia and dielectric relaxation as modeled by Champlin and Eisenstein (1978). It also includes the effect of the vanishing of the depletion region above the flat-band potential, as modeled by Crowe and Mattauch (1986). Our baseline calculation refers to a 1.4 μm diameter diode (Univ. of Virginia batch no. 1E12) operated at a carrier frequency of 2.52 THz and a modulation frequency of 8 GHz, as was used in the experiments of Watson, Grossman, and Phillips (1988). The effects on reflectivity modulation, and therefore on sideband-generation efficiency, of varying the diode parameters are investigated. Our conclusions are: A) For all realistic diode parameters, the phase modulation completely dominates the amplitude modulation. B) Performance is degraded well below the plasma frequency in the undepleted epilayer due to the presence of a second resonance, caused by the interaction of the barrier capacitance and the effective inductance due to carrier inertia, C) The effects of varying the antenna impedance, temperature, diode substrate size, and Schottky barrier height over realistic ranges are small. D) An improvement in single-sideband conversion efficiency of approximately 20 db may be obtained by increasing the epilayer doping and simultaneously reducing the diode radius.     

Measurement and study of the embedding impedance presented by the whisker antenna of a schottky diode corner cube mixer

A 250× scale model of a Schottky diode corner cube mixer designed for operation in the terahertz region has been built and tested. It has been successfully used to measure the embedding impedance presented to the diode at the whisker tip and also determine the impedance of the whisker antenna itself. The results have been input into a computer analysis to determine as to how the performance may be improved. With regards to improving the physical ruggedness of such mixers, a simple equivalent whisker structure has been determined and a new technique that may be used to fabricate a space qualifiable corner cube mixer intended for terahertz operation is disclosed.     

On the work mechanism of MIM point contact diodes

We have performed systematic measurements on a W-Ni MIM point contact diode at different IR, FIR, and IF frequencies in order to investigate the mechanisms responsible for the different response times observed in the diode operation. Our results led to the experimental confirmation of a second effect of thermal nature, besides tunnel effect, responsible for the diode operation. We measure the cutoff frequency of this second effect, which results in good agreement with our theoretical interpretation.     

Low frequency characteristics of a quasioptical Schottky diode detector part II: Experimental results

A detailed experimental study of the low frequency (video) response of a quasioptical Schottky diode detector over the microwave and FIR wavelength range is presented. An optimization of the responsivity versus the bias current is proposed and a generalized curve of the saturation power versus the FIR wavelength is given. This curve defines for any antenna point-contact Schottky diode detector, suitable for FIR detection, the power range for a linear detector response. A simple method is also described to calculate the coupling efficiency of the laser radiation into the antenna reception pattern.     

Theory of Infrared and Optical Frequency Amplification in Metal-Barrier-Metal Diodes

The near-infrared and optical frequency power gain of a metal-barrier-metal (MBM) point contact diode exhibiting a negative differential resistance region in its current-voltage characteristic is derived as a function of frequency. The diode is treated as a traveling-wave amplifier. The starting point for the analysis is the known electric and magnetic field distribution of the surface waves that propagate in the oxide barrier layer between the diode whisker and substrate, assuming no tunneling current is present. Then the differential tunneling conductance is introduced, and the electric and magnetic field distribution is used to find the propagation constant of the equivalent transmission line formed by the diode structure. It is shown that if the differential tunneling conductance is negative, gain can result. It is shown theoretically that the diode amplifier can provide approximately a 6-dB gain from the CO/sub 2/ laser frequency to the He-Ne laser frequency.     

Design considerations for planar Schottky barrier diodes

The cut-off frequency of the simplest planar Schottky diode on a uniformly doped n-layer of GaAs is derived. The theoretical results are given as functions of doping concentration and layer thickness with the specific contact resistance as parameter. An improved planar diode structure is presented with several short Schottky contact fingers connected in parallel. Experimental values ranging from 100 to 300 GHz agree with the calculated values when parasitic capacitances are taken into account.     

Report on 4H–SiC JTE Schottky diodes

4H–SiC Schottky diodes with and without Junction Terminate Extension (JTE) have been fabricated using Ni for contact and boron for p+ implant. Electrical characterization showed a rectifying behaviour in the on-state. In the reverse mode, the un-terminated Schottky diode demonstrated a breakdown voltage of approximately 200 V, while the JTE structure exhibited a significant improved breakdown performance, and the blocking voltage over 450 V. Optical microscope examination revealed the surface flashover failure located at the metal contact periphery for the un-terminated Schottky diode, while the JTE structure failed in the central area of the metal contact. Both the experimental and theoretical analyses confirmed the JTE structure enhancement on the reliability for SiC Schottky diode performance in reverse mode.     

Rectified Schottky diodes based on PEDOT:PSS/InGaZnO junctions

We report the successful use of the high-work-function, high-conductivity transparent conducting polymer PEDOT:PSS as the Schottky contact to form the Schottky junction (and thus Schottky diode) with the n-type semiconductor a-IGZO. The Schottky didoes exhibited a low apparent turn-on voltage, a high rectification ratio of >10⁵ at ±1 V, and a decent ideality factor of ∼1.5–1.6. Detailed junction properties were systematically analyzed from J-V and C-V characteristics of the diodes. We also demonstrated the applications of PEDOT:PSS/a-IGZO Schottky junctions to various types of Schottky diodes, including the flexible, the transparent, and the flexible transparent PEDOT:PSS/a-IGZO Schottky diodes, by using different substrates and different counter electrodes.     

Barrier height diminution in Schottky diodes due to electrostatic screening

Electrostatic screening in the metal contact of a Schottky (metal-semiconductor) diode is shown to influence the calculated electrical characteristics of the diode. A thin space-charge layer is formed at the surface of the metal contact by capacitively induced free charges, This results in a voltage dependent diminution of the barrier height of the diode that increases in magnitude with increasing semiconductor dielectric constant and carrier concentration. Predicted values of the barrier height diminution exceed those attributed to image forces or tunneling effects for materials with dielectric constants greater than about 20. In diodes using semiconducting ferroelectric or piezoelectric materials, an additional diminution of the barrier height results from free charges induced in the metal contact by a remanent polarization field or an externally applied mechanical stress. Current-voltage characteristics of a metal-semiconductor diode are shown to be significantly influenced by the electrostatic screening effect. A soft breakdown current as opposed to saturation current is predicted for reverse biases while an exponential forward current with an η coefficient exceeding unity is predicted for forward biases. Photoemission characteristics are also affected. A voltage-dependent diminution of the threshold energy for photoresponse is predicted. Capacitance-voltage characteristics, on the other hand, differ only slightly from those of an ideal Schottky diode except in the case of a ferroelectric diode where excessively large screening effects are possible.     

Specific contact resistance of the Ni/AuGe/nGaP system

This work studies the specific contact resistance for Ni/Au-Ge/nGaP system at the rectifying regime, i.e. for which the heat-treatment temperature is below 400°C and the I–V characteristics exhibit a rectifying behavior. The specific contact resistance is first computed by using the generalized majority carrier transport theory derived by Chang and Sze [1]. The computed theoretical results are then used to interpret the experimental data which are obtained by measuring the specific contact resistance, at zero bias, as a function of the temperature for as-deposited and heat-treated Ni/Au-Ge/nGaP Schottky diodes. Au/nGaP Schottky diodes are also fabricated to verify the theoretical results. It is found that the barrier height for the Ni/Au-Ge/nGaP system rises from the as-deposited value, 1.10±0.04 eV, to the value of the Ni/nGaP system, 1.27?0.02 eV, as the contact is heat-treated at various temperatures up to 360°C, the eutectic point of the Au-Ge system, and drops rapidly as the contact is heat-treated above 360°C. The barrier height rise is believed to be caused by the Ni in-diffusion toward the Au-Ge/nGaP interface during the heat-treatment. The smaller temperature dependence of the specific contact resistance for Schottky diode samples heat-treated above 360°C indicates that after heat-treatment above this temperature, an n⁺ layer is formed on the GaP surface. The theoretically computed results are used to fit the experimentally measured data to obtain the effective n⁺ doping concentrations and barrier heights.     

Forward transients in point contact diodes

This paper discusses some of the factors which have to be taken into account in the evaluation of point contact diodes for computer work in view of the forward transients which may be present. Oscillograms of forward transients are shown and comparisons of various diodes and operating conditions made. Material is presented to acquaint the engineer with the forward transients attributed to the spreading resistance of point contact diodes, and illustrate why they should be considered by designers of high speed pulse circuits.     

RF burnout dependence on variation in barrier capacitance of mixer diodes

A novel scheme to measure the VSWR and the "phase variation" of mixer diodes at high RF power levels is described. This experimental test system provides a nondestructive way of determining the power-handling capability of a mixer diode and also serves as an important tool in improving the burnout performance of point contact and Schottky barrier diodes.     

Fabrication and characterization of single ZnO microwire Schottky light emitting diodes

ZnO microwires were grown using noncatalytic chemical vapor deposition method. The average diameter of the ZnO microwires were about 30 μm with length of up to 1–1.5 cm. Single ZnO microwire Schottky light emitting diode was fabricated using Au as Schottky contact electrode and using Al as ohmic contact electrode. The current–voltage (I–V) characteristics of Schottky diodes reveal good rectifying behavior. The Schottky barrier height and ideality factor were calculated to be 0.78 eV and 4.3, respectively. Furthermore, distinct electroluminescence with ultraviolet and visible emissions was detected from this device at room temperature.     

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.     

太赫兹肖特基二极管技术研究进展

太赫兹肖特基二极管是太赫兹应用领域中非常重要的一种器件,它可以实现高频信号的混频和倍频,研制发展太赫兹肖特基二极管对于太赫兹技术有重要意义。本文首先介绍了太赫兹肖特基二极管的种类及性能表征,接着介绍国内外主要研究机构在太赫兹肖特基二极管方面的研制成果和进展,最后总结出研制太赫兹肖特基二极管的关键技术和发展方向。     

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.     

A 2-dimensional fully analytical model for design of high voltage junction barrier Schottky (JBS) diodes

A physics-based closed form analytical model for the reverse leakage current of a high voltage junction barrier Schottky (JBS) diode is developed and shown to agree with experimental results. Maximum electric field “seen” by the Schottky contact is calculated from first principles by a 2-dimensional method as a function of JBS diode design parameters and confirmed by numerical simulations. Considering thermionic emission under image force barrier lowering and quantum mechanical tunneling, electric field at the Schottky contact is then related to reverse current. In combination with previously reported forward current and resistance models, this gives a complete I-V relationship for the JBS diode. A layout of interdigitated stripes of P-N and Schottky contacts at the anode is compared theoretically with a honeycomb layout and the 2-D model is extended to the 3-D honeycomb structure. Although simulation and experimental results from 4H-Silicon Carbide (SiC) diodes are used to validate it, the model itself is applicable to all JBS diodes.