A comparison of silicon and gallium arsenide large signal IMPATT diode behaviour between 10 and 100 GHz

A large-signal computer simulation of an IMPATT diode has been used to investigate the differences between gallium arsenide and silicon IMPATT diodes. The variations of efficiency with frequency, current density, series resistance, amount of punch-through and reverse saturation currents are all investigated.With no ‘parasitic’ effects the silicon diode efficiency remains almost constant between 10 and 100 GHz, whereas the efficiency of gallium arsenide diodes is higher than that of silicon diodes at 10 GHz but decreases to the silicon diode efficiency at 100 GHz. A lower residual avalanche particle current in gallium arsenide diodes results in a higher susceptibility to reverse saturation currents. In silicon diodes the higher material resistivity affects the efficiency more than in gallium arsenide diodes, the removal of series resistance by having a punched-through diode does not necessarily increase the efficiency. The difference between experimental results quoted in the literature and the theoretical calculations are considered in terms of these effects. By considering the differences in ionization coefficients and velocities between the materials the lower efficiency of silicon diodes compared to gallium arsenide diodes is explained, also the lower breakdown voltage of gallium arsenide diodes compared to silicon diodes of the same frequency, and the ‘forward-bias’ effect found at high frequencies in gallium arsenide diodes.     

Current-gain characteristics of Schottky-barrier and p-n junction electron-beam semiconductor diodes

Measured and calculated current gains are presented for silicon, gallium-arsenide, and gallium-arsenide-phosphide electron-beam-semiconductor Schottky-barrier diodes. Silicon and gallium-arsenide-phosphide (GaAs0.7P0.3) diodes, having comparable critical voltages, provided current gains of 1400 and 960, respectively, at the beam voltage of 9 kV. A gallium-arsenide diode had a gain of 2100 at 12.7 kV. It is shown that Schottky-barrier diodes provide a good diagnostic tool for measurement of energy per electron-hole pair in semiconductors. The average pair energies for silicon, gallium arsenide, and gallium arsenide phosphide, determined by use of these diodes, were 3.6, 4.6, and 5.2 eV, respectively. Expressions for static and time-dependent current gains are derived for abrupt p-n-junction EBS diodes based on measured and simplified (constant) lineal densities of secondary-electron generation. It is shown that the current gain of p-n junctions is generally lower than that of Schottky-barrier diodes and decreases with increasing density of the semiconductor. For shallow (<0.2 µmr) silicon junctions, the calculated current gain is only slightly smalle. (<8 percent) than that of comparable Schottky-barrier diodes Measurements performed on a relatively deep (0.8 µm) silicon p-n junction, which provided a current gain of 2500 at the beam voltage of 13.6 kV, are in good agreement with the theory. The gain of this junction was typically 40 percent lower than that of a comparable Schottky-barrier diode. This difference was significantly greater for gallium arsenide as a result of its higher density. Approximate expressions and calculations are presented for estimating frequency limitations of p-n-junction EBS targets.     

A theoretical assessment of low and high bandwidth gallium arsenide,germanium and silicon avalanche photodiodes for optical communication systems

A comparison is made of the relative properties of avalanche photodetectors for use in optical communication systems operating up to 1 GHz bandwidth over the wavelength range 730–1130 nm. Detectors for optical communications systems may have to operate at voltages limited by the electrical feeds to repeaters, hence the present comparison is for the specific case of diodes with a maximum operating voltage. The voltage used is generally 100V, but the analysis is also extended to 200V.The speed of the diodes is considered briefly then the main analysis compares the signal to noise performance of gallium arsenide, germanium and silicon diodes. The most recent noise theory is used incorporating the frequency dependence of multiplication and a detailed comparison is made of the results and their differences for the three materials analysed. In addition comparison is made with results using less accurate theories.The optimum diode material, for the simple uniformly doped 100V diodes considered, varies with wavelength and frequency. However the results show that there is no clear-cut choice and that, for instance, at long wavelengths (i.e. greater than 1·05 nm) germanium diodes, despite their high dark current, have comparable or better performance than silicon diodes for operation at 100V. Similarly in the conditions considered gallium arsenide photodiodes might provide an alternative detector for high frequency systems using gallium aluminium arsenide lasers.     

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.     

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.     

High-power generation in IMPATT devices in the 100-200-GHz range

A silicon double-drift IMPATT diode with high uniform doping levels was simulated. Simulation results show that it is possible for silicon IMPATT diodes to generate extremely high pulsed output power for frequencies above 100 GHz under high current-density operation. The highest output power matched to a 1-Ω load resistance obtained at 150 GHz is 37.7 W with a DC current density of 200 kA/cm², although the calculated power conversion efficiency is low. It is also shown that the low-power conversion efficiency limits the diode's continuous wave power operation     

Microwave mixer and detector diodes

Recent advances in microwave mixer and detector diodes are reviewed. Devices considered are germanium back diodes, silicon and gallium arsenide point-contact diodes, and Schottky-barrier diodes. Current work on low-barrier (n-type) Schottky diodes and high-burnout point-contact diodes is also described. Experimental results of CW and RF pulse burnout of these devices are summarized. Different approaches to improve the power-handling capability of Schottky diodes at S-, X-, and Ku-band frequencies are considered.     

Comparison of theoretical and experimental 60 GHz silicon IMPATT diode performance

Theoretical and experimental investigations have been carried out for V-band (50-75 GHz) silicon double drift flat profile (DD) and double low high low (DLHL) IMPATT diodes. The theoretical designs have been used for the experimental realisation of the diodes for CW operation. The epitaxial layers were grown by silicon molecular beam epitaxy which enabled the realisation of the complex DLHL profile at millimetre-wave frequencies in the silicon material system for the first time. The maximum obtained conversion efficiency is 14.3%. A comparison of theoretical and experimental results for both types of diodes shows general agreement and the superiority of the DLHL structure.<>     

Low noise wide bandgap SiC based IMPATT diodes at sub-millimeter wave frequencies and at high temperature

We have presented a comparative account of the high frequency prospective as well as noise behaviors of wide-bandgap 4H-SiC and 6H-SiC based on different structures of IMPATT diodes at sub-millimeter-wave frequencies up to 2.18 THz. The computer simulation study establishes the feasibility of the SiC based IMPATT diode as a high power density terahertz source. The most significant feature lies in the noise behavior of the SiC IMPATT diodes. It is noticed that the 6H-SiC DDR diode shows the least noise measure of 26.1 dB as compared to that of other structures. Further, it is noticed that the noise measure of the SiC IMPATT diode is less at a higher operating frequency compared to that at a lower operating frequency.     

Millimeter-wave GaAs read IMPATT diodes

We have designed, fabricated, and evaluated gallium arsenide Read IMPATT diodes for Ka-band (36-38 GHz)operation. The devices were packaged units intended for manufacturability and high yield. Oscillator output power as high as 710-mW CW was obtained at 9-percent efficiency. This paper describes design and fabrication techniques employed and discusses the potential and limitations of such devices.     

Sweep oscillation mode of GaAs IMPATT diode

Properties of the sweep oscillation mode of GaAs IMPATT diodes in the millimeter-wave region are studied in comparison with Si IMPATT diodes. In spite of their narrower depletion width, the GaAs diodes oscillate at lower frequencies than the Si devices. This can be explained by using the newly measured drift velocity of GaAs.     

Computer optimisation of double-drift-region IMPATT diodes

Design parameters for double-drift-region silicon IMPATT diodes for frequencies from 10 to 100 GHz are presented. The design is based on extensive large-signal computer simulations at one frequency of two different diode structures in a simple circuit. From these simulations, a simple design criterion was derived which permits the calculation of optimised impurity profiles for any desired frequency, with a small computer effort.     

Low-high-low profile gallium arsenide IMPATT reliability

The reliability of low-high-low gallium arsenide IMPATT diodes has been studied. The devices were fabricated from vapor phase grown epitaxial gallium arsenide using sputtered platinum Schottky junctions and plated heat sink construction. Various screening methods have been evaluated for use in burn-in, and 75°C case dc burn-in at rated power dissipation selected as the best compromise. Long-term operation tests have established a minimum MTBF at 90-percent confidence of 34 000 h. RF and storage step stress tests have revealed a potential failure mechanism involving separation of the metallization layers. An improved metallization system has been established eliminating this mechanism. Various additional tests have demonstrated the immunity of these IMPATT's to damage from on-off switching transients, load mismatch, and bias voltage transients.     

Tunneling-assisted IMPATT operation

The influence of tunneling on the efficiency of millimeter-wave IMPATT diodes is investigated. For a reliable estimation of this influence, the tunnel generation rate coefficients are measured from silicon p-i-n diodes. The Read equation is solved taking a time-dependent tunnel current into account. The phase distortion, which is responsible for the efficiency degradation caused by tunneling, is calculated analytically and numerically. It is shown that for an exact solution the injected current density should be calculated numerically. The results suggest that for efficient silicon IMPATT diode operation, the maximum electric field should be below 1×10⁶ V/cm. Due to the current and field dependent representation of the injection phase, there are direct consequences on the design of millimeter- and submillimeter-wave transit time diodes for high power generation as well as for low-noise operation     

High-efficiency continuous oscillations in silicon IMPATT diodes below the transit-time frequency

C.W. room-temperature operation of silicon IMPATT diodes at the first subharmonic of the transit-time frequency has been observed in a high-efficiency mode. Efficiencies as high as 8.8% at 5GHz with 1.2 Wc.w. have been achieved with current densities no more than 1480A/cm2.     

Influence of the operating temperature on the design andutilization of 94-GHz pulsed silicon IMPATT diodes

The RF and thermal behavior of 94-GHz P⁺PNN⁺ double drift flat doping profile silicon impact ionization avalanche transit time (IMPATT) diodes for high-power pulsed operation is investigated by means of time domain electrical oscillator models. It is demonstrated that these diodes have a limited optimum temperature range of operation, associated to specific matching and bias conditions, to achieve a stable and high power operation. This restriction necessitates a thermal control when the oscillator must operate over a wide ambient temperature range. Highly doped, short active zone length diodes appear to have the best potential for high power performance     

Current tuning and the concept of avalanche resonance in IMPATT diodes under large signal operating conditions

The concept of current tuning, i.e. the increase of optimum frequency with current density, is well-known in IMPATT diodes. An explanation of the phenomenon by postulating an avalanche resonance frequency was derived by Gilden and Hines from small-signal theory. Difficulties arise however when the small-signal theory is extrapolated to large signal operation. This paper provides a coherent explanation of the zero conductance and susceptance frequencies (which can be related to the avalanche resonance concept in an idealised diode model) and current tuning by utilizing a modified approach to Gilden and Hines theory which can then be extrapolated to large signal behaviour. Large signal computer simulation of diodes is used to verify the conclusions on the zero conductance and susceptance frequencies and current tuning under large signal conditions with varying frequency, drive level and current density. By examining the waveforms of the simulated diodes the cause of the zero conductance frequency (avalanche resonance at small signal levels) and current tuning can be shown to be due to the perturbation of the avalanche region electric field by the space charge of the drifting charge bunch.     

IMPATT operation below the avalanche frequency

Very high output powers are obtained with double drift IMPATT diodes at current densities which shift the avalanche frequency above the oscillation frequency: 30-40 W pulsed around 90 GHz. This operation mode cannot be explained in terms of the conventional READ theory. A numerical large signal simulation shows that avalanche multiplication over the whole diode takes place. At high current densities the double drift device behaves like a pin diode without the unfavourable breakdown of the ionisation process in the centre of the diode.<>     

Millimeter-Wave CW IMPATT Diodes and Oscillators

This paper summarizes the current state of the art of silicon CW millimeter-wave IMPATT diodes and oscillators in the frequency range from 30 to 250 GHz. Design procedures, fabrication, and packaging technology are reviewed, and the current performance of diode oscillators is reported. A brief account of present device reliability is also presented. The contrast between maturing device technology below 100 GHz and largely laboratory-based technology at higher frequencies is discussed. Finally, a prognosis of future developments is offered.     

Efficiency limitation by transverse instability in Si IMPATT diodes

Measurements of large-signal impedance, ac voltage and dc voltage V0versus dc current I0on Si p-n-n⁺IMPATT diodes in pulse operation (80 ns) suggest that the efficiency of Si IMPATT diodes is limited by instability effects causing a splitup into regions with different current densities. The effect is explained by considering the I0-V0curves at constant ac voltage. These can be S-shaped owing to impact ionization in the drift region.