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.<>     

A study of the power handling ability of gallium arsenide and silicon,single and double drift IMPATT diodes

The concept of a critical current density effect on the operation of silicon and gallium arsenide IMPATT diodes is examined using large signal analysis. This critical current density effect does not appear to exist in the form that is generally thought of to-date. However, other physical processes develop at high current densities which gradually degrade diode efficiencies. These processes are worse in silicon diodes than in gallium arsenide diodes because at a given frequency of operation silicon diodes need a lower doping density than gallium arsenide diodes due to the lower saturated drift velocities of carriers in gallium arsenide. Reasons are suggested which explain why these other processes develop before a true critical current density limit is seen. New scaling data for limits on power handling ability vs frequency of gallium arsenide IMPATT diodes are presented. In addition the advantages of double drift structures over single drift structures are re-examined in the light of the suggestion that silicon and gallium arsenide IMPATT diodes are thermally and impedance limited rather than current density limited at high frequencies. The problem of tunnelling is also examined and is shown to be unimportant at all frequencies up to 120 GHz.     

A 50-GHz silicon IMPATT diode oscillator and amplifier

Recent experimental observations on a silicon impact avalanche transit-time diode oscillator and amplifier CW-operated at 50 GHz are presented. 1) CW oscillation power of 100 mW was obtained at an overall efficiency of 2 percent. The oscillation frequency was continuously tunable over a 1.3-GHz range by a sliding short. 2) Phase-locking has been achieved with a maximum normalized gain-bandwidth product of 0.1. The minimum locking signal power required for a 500-MHz locking bandwidth was 20 dB below the oscillator output. 3) Electronic tuning of the oscillator frequency was demonstrated by placing a millimeter-wave varactor diode in the tuning circuit. The output frequency versus the bias voltage on the varactor diode was linear with maximum frequency deviation of 300 MHz. Frequency modulation of the oscillator by driving the varactor with a sinusoidal source was obtained at a modulation frequency of 50 MHz. 4) Stable amplification with 13-dB gain was obtained, centered at 52.885 GHz with a 3-dB bandwidth of 1 GHz. The maximum output power obtained was 16 mW. Higher gain of about 17 dB was obtained at a reduced bandwidth. The noise figure of the amplifier was 36 dB. Equivalent circuits for the oscillator and the amplifier are derived. The calculated results agree reasonably well with the experimental observations.     

Cost trade between multijunction,gallium arsenide and silicon solar cells

Multijunction (MJ),¹ gallium arsenide (GaAs) and silicon (Si) solar cells have respective test efficiencies of approximately 24%, 18.5% and 14.8%. Multijunction and gallium arsenide solar cells weigh more than silicon solar cells and cost approximately five times as much per unit power at the cell level.² A trade is performed for the Tropical Rainfall Measuring Mission (TRMM) spacecraft to determine which of these cell types would have offered an overall performance and price advantage to the spacecraft. A trade is also performed for the multijunction cells under the assumption that they will cost over ten times that of silicon cells at the cell level. The trade shows that the TRMM project, less the cost of the instrument, ground systems and mission operations, would spend approximately $552 000 per kilogram to launch and support

1 The term ‘support’ means to provide the scientific equipment (‘science’) with environmental protection from the space environ ment, to keep it at acceptable temperatures and to send the data it produces to Earth in readable form, i.e. the services provided by the spacecraft.

science in the case of the spacecraft equipped with silicon solar cells. If these cells are exch anged for gallium arsenide solar cells, an additional 31 kg of science can be launched and serviced at a price of approximately $90 000 per kilogram. The 31 kg array weight reduction is shown to derive from the smaller area of the array and hence reductio ns in the weight of the array substrate and supporting structure. If the silicon solar cells are changed out for multijunction solar cells, an additional 45 kg of science above the silicon baseline can be launched and supported at a price of approximately $58 000 per kilogram. The trade shows that even if the multijunction cells are priced over ten times that of silicon cells, a price that is much higher than projected, the additional 45 kg of science are launched and serviced at $180 000 per kilogram. This is still much less than the original $552 000 per kilogram to launch and service the science. Data and qualitative factors are presented to show that these figures are subject to a great deal of uncertainty. Nonetheless, the benefit of the higher efficiency solar cells for TRMM is far greater than the uncertainties in the analysis. © This article is a US Government work and, as such, is in the public domain in the United States of America     

The diffusion of silicon in gallium arsenide

The rate of diffusion of silicon from a sputtered film of silicon into gallium arsenide has been studied as a function of the ambient arsenic pressure at 900 and 1000°C. The diffusion appears to be non-Fickian. The saturated surface concentration of silicon in diffused layers is about 0·3 wt per cent and the average electron concentration of the layers is about 5 × 10¹⁸ cm⁻³. Silicon has been used as an emitter diffusant in a double diffused GaAs transistor.     

A large signal analysis of IMPATT diodes

This paper presents results on RF power output and efficiency of IMPATT oscillators obtained from a large-signal model of these devices. The results are obtained from a closed-form solution of the nonlinear equations describing a Read-type IMPATT diode. The closed-form solution is obtained by assuming a short transit time through the drift region compared to the RF period. The solution is used to obtain the large-signal diode impedance. The analysis shows that the power output of an IMPATT diode depends strongly on the series load resistance presented to the active part of the diode and that the change in diode reactance with increasing bias current also depends on the series resistance. Plots of power output as a function of frequency, bias current, and load resistance are presented. Frequency tuning of the oscillator through current variation is also discussed. Experimental results are presented and compared with the theoretical ones wherever possible. The results lead to an improved understanding of such oscillators and are extremely useful in optimizing their performance and determining their limitations.     

Capless annealing of silicon implanted gallium arsenide

Numerous commercially available semi-insulating GaAs substrates have been implanted with silicon ions and the post implantation annealing carried out using the technique of capless annealing in an arsine atmosphere. Results are presented on the implanted atomic silicon distribution along with carrier concentration and mobility profiles, Hall mobility and percentage activation figures for various implanted substrates. The phenomenon of thermally induced surface conduction layers in semi-insulating GaAs is discussed in the context of a capless annealing technique.     

Radiation-thermal activation of silicon implanted in gallium arsenide

The layer density, density profile, and mobility of electrons in ²⁸Si-ion-doped layers of semiinsulating GaAs after radiation annealing with electron energy above and below the defect formation threshold and after thermal annealing in the temperature range T _a =590–830 °C are investigated. It is shown that for radiation annealing energy above the defect formation threshold ion-doped layers are formed with much lower annealing temperatures, and the degree of electrical activation of silicon in these layers is high and the density of electron mobility limiting defects is low. Fiz. Tekh. Poluprovodn. 33, 687–690 (June 1999)     

The potentialities of silicon and gallium arsenide solar batteries

The theory of the spectral response of a p-n junction solar battery unit is given, and detailed comparisons are made of the expected performance of silicon and gallium arsenide units. Data now available on absorption in GaAs show that it is a particularly favourable material because it has a very steep absorption edge. The low effective masses and correspondingly low densities of states in GaAs are also advantageous.

The efficiency of practical Si units is unlikely to exceed 15 per cent even with intensive development, whereas GaAs units with efficiencies of about 20 per cent should be achievable in the near future and the performance may ultimately approach 25 per cent, even if (as assumed) the carrier lifetimes stay well below those for Si.     

Detectivity of gallium arsenide on silicon substrate photoconductive detectors

Planar photoconductors made with GaAs on silicon substrate have been studied with respect to static and dynamic responsivities as well as noise levels, in the 1 Hz-100 kHz frequency range. The results obtained have led to the determination of the specific detectivity which is in turn compared to those of GaAs planar photoconductors and Si photodiodes.<>     

Effect of optical illumination on DDR IMPATT diode at 36 GHz

A reverse biased p-n junction diode with proper resonant cavity and boundary conditions is able to generate rf power and shows normal DC and small signal properties designed with semiconductor materials like 4H-SiC, GaAs, InP, Si-based DDR IMPATT structure at Ka band with dark condition. But when it is exposed to optical illumination through a proper optical window for both top mounted (TM) and flip chip (FC) configuration, it shows the influence on the oscillator performances in that band of frequency. The simulated results are analyzed for 36 GHz window frequency in each of the diodes and relative differences are found in power output and frequency of all these diodes with variable intensities of illumination. Finally it is found that optical control has immense effect in both FC and TM mode regarding the reduction of output power and shifting of operating frequency from which optimization is done for the best optically sensitive material for IMPATT diode.     

Effect of external actions on characteristics of gallium arsenide Schottky-barrier diode structures

In this paper we analyze briefly literary information about an effect of external actions on electrophysical characteristics of gallium arsenide Schottky-barrier diode structures and their stability to external influences. We discussed radiation changes of gallium arsenide Schottky-barrier diode structures, and also we discuss effects of small radiation dose treatment.     

Large-signal analysis of Lo-Hi-Lo double-drift silicon IMPATT diodes at 50 GHz

Large-signal analysis of a lo-hi-lo double-drift silicon IMPATT diode at 50 GHz shows that the device is capable of output power of 1.1 W and efficiency of 20 percent for a device area of 2 × 10^-5cm²at a dc biasing current density of 12 kA/cm²and ac voltage amplitude of 12 V. It is also found that, both output power values and efficiencies decrease with increasing enhanced leakage current.     

Theoretical efficiency of the l.s.a. mode for gallium arsenide at frequencies above 10GHz

The efficiency of the l.s.a. mode is calculated for galliumarsenide diodes taking account of all the electron-lattice relaxation processes. The efficiency falls off with increasing frequency and typically becomes negative above 100GHz.     

Free space video detection of harmonic content of 100 GHz IMPATT oscillator

The harmonic content of a commercial c.w. 20 mW 100 GHz IMPATT oscillator operating at ambient temperature has been determined at 200 and 300 GHz using free space techniques. The highest power levels observed at these frequencies were 16.6 and 37.5 dB below the fundamental, respectively, corresponding to power levels of 0.5 mW at 200 GHz and 4.5 ?W at 300 GHz at the oscillator.     

Investigation of the charge carrier concentration and electric field distribution in gallium arsenide Gunn diode

Numerical calculation of the stationary distribution of electric field and charge carrier concentration in Gunn diode has been performed for the one-dimensional case. In addition, experimental investigations of the specified characteristics were also carried out by using a near-field microwave microscope. Taking into account the dependence of the majority carrier diffusion coefficient on the electric field intensity was shown to be of crucial importance in describing the processes occurring in Gunn diodes. The numerical results were in good agreement with the results of conducted experiment.