Impact ionization wave breakdown of drift step recovery diodes

High frequency IMPATT oscillations followed under certain conditions by reversible impact ionization wave breakdown of the p ⁺-n-n ⁺ diode structure have been experimentally observed for the first time in a drift step recovery diode operating in the avalanche breakdown mode after a fast voltage restoration of the p-n junction.     

Heat flow resistance measurements of silicon p+-v-n+ diodes under forward and reverse biased conditions

A detailed study of the heat flow resistance measurements in a p⁺-v-n⁺ diode is studied in both forward and reverse biased conditions. Measurements are made by continuously switching the diode from the power dissipation state into the temperature measuring state. Safe operating power limits are identified for the diodes depending upon their mode of operation either as a microwave switch or as an IMPATT oscillator.     

Estimation of power density in IMPATT using different materials

ABSTRACT

The RF output power dissipated per unit area is calculated using Runge-Kutta method for the high-moderate-moderate-high (n⁺-n-p-p⁺) doping profile of double drift region (DDR)-based impact avalanche transit time (IMPATT) diode by taking different substrate at Ka band. Those substrates are silicon, gallium arsenide, germanium, wurtzite gallium nitride, indium phosphide and 4H-silicon carbide. A comparative study regarding power dissipation ability by the IMPATT using different material is being presented thereby modelling the DDR IMPATT diode in a one-dimensional structure. The IMPATT based on 4H-SiC element has highest power density in the order of 10¹⁰ Wm^?2 and the Si-based counterpart has lowest power density of order 10⁶ Wm^?2 throughout the Ka band. So, 4H-SiC-based IMPATT should be preferable over others for the power density preference based application. This result will be helpful to estimate the power density of the IMPATT for any doping profile and to select the proper element for the optimum design of the IMPATT as far as power density is concerned in the Ka band. Also, we have focused on variation of power density with different junction temperatures and modelled the heat sink with analysis of thermal resistances.     

Potentials of GaP as millimeter wave IMPATT diode with reference to Si, GaAs and GaN

This paper presents the simulation results of DC,small-signal and noise properties of GaP based Double Drift Region( DDR) Impact Avalanche Transit Time( IMPATT) diodes. In simulation study we have considered the flat DDR structures of IMPATT diode based on GaP,GaAs,Si and GaN( wurtzite,wz) material. The diodes are designed to operate at the millimeter window frequencies of 94 GHz and 220 GHz. The simulation results of these diodes reveal GaP is a promising material for IMPATT applications based on DDR structure with high break down voltage( V_B) as compared to Si and GaAs IMPATTs. It is also encouraging to worth note GaP base IMPATT diode shows a better output power density of 4. 9 × 10~9 W/m~2 as compared to Si and GaAs based IMPATT diode. But IMPATT diode based on GaN( wz) displays large values of break down voltage,efficiency and power density as compared to Si,GaAs and GaP IMPATTs.     

Low-Complexity Full-Melt Laser-Anneal Process for Fabrication of Low-Leakage Implanted Ultrashallow Junctions

Good-quality ultrashallow n ⁺ p junctions are formed using 5-keV amorphizing As⁺ implantations followed by a single-shot excimer laser anneal for dopant activation. By using an implant that is self-aligned to the contact windows etched in an oxide isolation layer, straightforward processing of the diodes is achieved with postimplantation processing temperatures kept below 400°C. A possible source of junction leakage at the perimeter caused by dip-etch enlargement of the contact window, also confirmed by transmission electron microscopy (TEM) analysis, is identified, and diode performance is improved by increasing the junction/contact window overlap. The optimum performance in terms of low leakage, shallow junctions, and low resistivity is achieved for 30° tilted implants and by applying a thin laser-reflective aluminum layer. This work isolates the minimum requirements for achieving low-leakage diode characteristics.     

Low-frequency high-efficiency oscillations in germanium IMPATT diodes

Pulsed operation of germanium IMPATT diodes has produced oscillations from 10 MHz to 12 GHz, with efficiencies exceeding 40 percent for frequencies between 2 and 3 GHz. Recorded waveforms show that IMPATT oscillations are required to initiate the lower frequency high-efficiency modes. The diodes are epitaxial diffused junction n-p-p⁺mesa structures, with depletion widths ∼ 5 microns and breakdown voltages ∼ 60 volts. Typical diode area is2 times 10^{-4}cm². Static I-V curves, obtained with circuit conditions which do not permit any oscillations, exhibit positive incremental resistance. The usual IMPATT mode would be expected to be between 6 and 12 GHz. Operation at frequencies below the IMPATT frequency requires circuit conditions suitable for IMPATT oscillations to be present to initiate the lower frequency, higher efficiency mode. This mode is characterized by a sudden decrease in diode voltage and a simultaneous increase in current, similar to that reported for silicon devices [1]. Reproducible current and Voltage waveforms have been recorded for four distinctly different low-frequency modes of operation which result only from changes in the ac circuit seen by the diode.     

Effect of growth temperature on diode parameters of n-ZnO/p-Si heterojuction diodes grown by atomic layer deposition

n-ZnO/p-Si heterojunctions were grown by atomic layer deposition (ALD) on (100) p-Si substrates at different growth temperatures in the range of ~100–250 °C. The current-voltage characterization of all the heterojunctions showed typical rectifying behavior, a true signature of a p-n junction diode. The diode grown at 100 °C were having significantly lower reverse saturation current (~21 nA) and high rectification factor (~120) compared to those grown at relatively higher temperatures such as 200 or 250 °C. From capacitance-voltage measurements, it was found that the depletion width in the ZnO side of n-ZnO/p-Si diode was maximum (~60 nm) for the diode grown at 100 °C and decreased gradually to ~3 nm for the diodes grown at high temperatures of 250 °C. The electron concentration in ZnO films was found to increase significantly on increasing the growth temperature from ~100 to 250 °C. The junction capacitance also showed an increasing trend with increase in the growth temperature. The variation of diode parameters with growth temperature has been discussed in terms of carrier concentration in ZnO films and associated growth mechanisms of the ALD. Such low temperature grown n-ZnO/p-Si diodes with lower reverse saturation current and large depletion width may be suitable for photo detection applications.     

Physical understanding and optimum design of high-powermillimeter-wave pulsed IMPATT diodes

A physical understanding of the specific mode of operation of high-power millimeter-wave pulsed IMPATT diodes is derived from a self-consistent numerical model. It is shown theoretically that there exists a uniformly avalanching p-i-n-like mode in high-current-density, pulsed silicon double-drift IMPATT diodes, as has been previously suggested. An optimum symmetrical flat doping-profile double-drift structure for 100-GHz operation is presented. It could deliver more than 40 W of available peak power with a 10% conversion efficiency accounting for circuit losses, at a safe junction temperature rise. The theoretical results allow an optimum design of the 94-GHz IMPATT structure for peak output power in excess of 50 W under low duty cycle     

Thermal runaway of IMPATT diodes

A simple one-dimensional computer model of the dc-thermal behavior of a Schottky-barrier GaAs IMPATT diode has been formulated to compute the conditions for thermal runaway in IMPATT diodes of various designs. The model has been used to determine the thermal stability conditions for three designs of GaAs IMPATT's. The computations lead to several conclusions, the most important of which are the following. a) Junction thermionic emission (leakage) current is thermally unstable, whereas avalanche multiplication is thermally stabilizing. Diode thermal stability at high junction temperature requires that the thermionic emission current be low and the avalanche multiplication be large. b) Lowering of the barrier height caused by contaminants or defects at the junction increases the likelihood of thermal runaway. c) For a given barrier height, the higher the doping of the IMPATT diode, the more resistant it will be to thermal runaway.     

Dependency of the highest harmonic oscillation frequency on junction diameter of IMPATT diodes

The effect of series resistance and junction capacitance on the high-frequency limit of IMPATT diode operation is studied with a Read-type small-signal theory, and is confirmed experimentally. Oscillation frequencies from 30 to 400 GHz have been measured with Si p⁺-n-n⁺abrupt junction diodes with a depletion layer width of 0.2 µm. The highest oscillation frequency increases as the junction diameter is decreased, owing to reduced junction capacitance and increased bias-current density. The highest oscillation frequency observed is 423 GHz, which is obtained in the fifth harmonic mode with a diode of 16-µm junction diameter. Fundamental oscillation frequency is found to depend strongly on dc bias-current density, and to be close to the avalanche frequency of the small-signal theory.     

Chaotization of Oscillations in a Single-Frequency Millimeter-Band Impact Avalanche and Transit-Time Diode Oscillator under the Influence of a Low-Frequency Harmonic Oscillation

The change in the oscillation spectrum of an oscillator based on an impact avalanche and transit-time (IMPATT) diode of the 7-mm range under the action of a low-frequency harmonic oscillation (3 MHz) in the supply circuit of the diode is studied experimentally. It is demonstrated that, if the low-frequency oscillation amplitude exceeds the trigger negative voltage and the working point in the diode volt–ampere characteristic is located either near the trigger current (trigger negative voltage) or far from it, pulsed oscillation mode is established and, consequently, oscillations are chaotized.     

MOCVD-grown InGaAs/GaAs/AlGaAs laser structures with a broad-area contact

A metal-organic chemical vapor deposition (MOCVD) technique is developed for a diode laser heterostructure in a system of InGaAs/GaAs/AlGaAs solid solutions; the optimal sizes and the doping profile of the structure are determined to minimize the internal optical losses. Mesa-strip diode lasers with a threshold density of current J _th=150–200 A/cm², internal optical loss factor α_i=1.6–1.9 cm^?1, and an internal quantum yield η_i=85–95% were fabricated. In the continuous lasing mode of a diode laser with a 100-µm-wide aperture and a wavelength of 0.98 µm, the optical power output was as high as 6.5 W and was limited by the catastrophic optical degradation of mirrors. The radiation divergence in the plane normal to the p-n junction amounts to θ_⊥. The use of wide-gap waveguide layers, which deepens the potential electron well in the active region, is shown to reduce the temperature sensitivity of the InGaAs/GaAs/AlGaAs laser heterostructures in the temperature range from 0 to 70°C.     

Design Consideration for Frequency-Stabilized MIC IMPATT Oscillators in the 26-GHz Band

A 26-GHz frequency-stalbilized MIC IMPATT oscillator using a dielectric resonator has been developed. In designing such an oscillator in the high-frequency range, many parameters affecting frequency stability should be considered. This paper discusses oscillation frequency variations caused by deviations in the resonant frequency of dielectric resonators, in diode reactance, and in the electrical length between the diode and resonator, all of which are due to temperature variation. Design criteria for a highly frequency-stabilized oscillator are also presented. With these techniques, we have obtained an MIC IMPATT oscillator with frequency stability of less than +-5.0x10/sup -5/, output power deviation of less thau +-2.0 dB, and output power of more than 23 dBm over the temperature range of 0°C to 50°C.     

The Traveling-Wave IMPATT Mode

The small-signal analysis of a distributed IMPATT diode ifdicates the existence of a traveling-wave mode. The severe power-frequency limitation as well as the associated low impedance level of the discrete diode appear avoidable. No external resonant circuitry is needed. It is shown that the TEM parallel-plate waveguide mode of the junction is modified by the injection of electrons at the p+ -n junction (or Schottky contact). The transverse electric field takes on a traveling-wave nature in the transverse direction tracking the injected electrons, and a small longitudinal electric field will also be present. In previous papers on IMPATT traveling-wave structures, the IMPATT effect was lumped into an effective complex permittivity in a composite layer model or into an effective shunt admittance in a transmission line model. The current work attempts to incorporate the IMPATT mechanism into the wave model and considers the actual carrier field interaction. The srnall-signal analysis yields an analytic field solution and a characteristic equation for the complex propagation constant. Solutions are found and documented for various frequencies and bias current densities. For the particular structure considered, at 12 GHz with a bias current density of 1000 A/cm/sup 2/ a gain of 72 dB/cm was found.     

Photoelectrical Characteristics of a C/CNx Multiwalled Nanotube

A nanotube diode fabricated from a single C/CN_x multiwalled nanotube exhibits a large photocurrent and a large photovoltage under illumination. The current–voltage (I–V) characteristics of the diode indicate a clear rectification effect. By comparing the I–V characteristics of C, CN_x, and C/CN_x nanotube diodes, we show that the rectifying characteristics of the C/CN_x diode arises from the molecular junction formed at the C/CN_x interface where the C and CN_x segments are chemically bonded. External radiation photochemically generates electrons and holes in the C/CN_x nanotube, producing a large photocurrent because of the influence of the strong electric field in the vicinity of the C/CN_x junction. These unique photoresponsive characteristics of C/CN_x nanotube junction diodes points to potential applications such as photovoltaic devices and photodiodes.     

Thermally Stable Hole‐Transporting Materials Based upon a Fluorene Core

We report a new class of diamine hole‐transporting materials (HTMs) based upon a fluorene core. Using a fluorene core, rather than a biphenyl group, leads to enhanced thermal stability, as evidenced by glass‐transition (T_g) temperatures as high as 161 °C for N,N′‐iminostilbenyl‐4,4′‐fluorene (ISF). The fluorene‐based HTMs have lower ionization potentials (I_p) than their biphenyl analogs, which leads to more efficient injection of holes from the indium tin oxide (ITO) anode, and higher quantum efficiencies. Devices prepared with fluorene‐based HTMs were operated under thermal stress. The failure of an organic light‐emitting diode (OLED) under thermal stress has a direct correlation with the thermal stability of the HTM that is in contact with the ITO anode. OLEDs based on ISF are stable to over 140 °C.     

Polyarylene Networks via Bergman Cyclopolymerization of Bis‐ortho‐diynyl Arenes

Bis‐ortho‐diynylarene (BODA) monomers, prepared from common bisphenols in three high yielding steps, undergo free‐radical‐mediated thermal polymerization via an initial Bergman cyclo‐rearrangement. Polymerization is carried out at 210 °C in solution or neat with large pre‐vitrification melt windows (4–5 h) to form branched oligomers containing reactive pendant and terminal aryldiynes. Melt‐ and solution‐processable oligomers with weight‐average molecular weight M_w = 3000–24 000 g mol^–1 can be coated as a thin film or molded using soft lithography techniques. Subsequent curing to 450 °C affords network polymers with no detectable glass transition temperatures below 400 °C and thermal stability ranging from 0.5–1.5 % h^–1 isothermal weight loss measured at 450 °C under nitrogen. Heating to 900–1000 °C gives semiconductive glassy carbon in high yield. BODA monomer synthesis, network characterization and kinetics, processability, thin‐film photoluminescence, and thermal properties are described.     

200-Megabit-pulsed avalanche oscillation with Ge silver- bonded diode in 50-GHz region

Some experimental results with an IMPATT diode operating in the 50-GHz region are presented, including 200-megabit- pulsed avalanche oscillation, injection locking, frequency spectra of the free running oscillation and the locked oscillation, and the noise spectra around the avalanche oscillation.