Intrinsic AM noise in singly tuned IMPATT diode oscillators

Analytical relationships are derived for the ratio of the intrinsic AM to FM noise, and for the intrinsic AM noise of IMPATT diode oscillators. The theory is confirmed experimentally for a silicon n⁺-p diode and an n-gallium-arsenide Schottky barrier diode operating at low and intermediate signal levels.     

A theory of noise in GaAs FET microwave oscillators and its experimental verification

A theory has been developed which provides an entirely analytical approach to the calculation of AM and FM noise in free-running GaAs FET microwave oscillators. The theory is based on the model that low-frequency device noise is mixed with the carrier signal via the nonlinearity of the FET and upconverted to microwave frequencies. Because of the analytical nature of the theory, all the important device and circuit parameters on which the noise generation depends are explicitly given. Two GaAs FET oscillators have been fabricated and used to investigate the FM noise. The theory predicts well both the spectral dependence and the absolute magnitude of the FM noise in both oscillators. The noise performance of the oscillators differs by 19 dB. The theory indicates that no single factor is responsible for this, and moreover that attention should be given to the optimization of many device and circuit features in the design of a low noise FET oscillator.     

Investigation of parasitic oscillations in IMPATT-diode oscillators by a simple locus chart

Using a simplified theory of parasitic oscillations in IMPATT-diode oscillators, a locus chart is constructed that facilitates the study of parasitic oscillations of the degenerate type. Results of experiments on a high-Q factor coaxial/waveguide circuit (Kurokawa circuit) are explained by this locus chart.     

Efficiencies of Schottky-barrier GaAs and both complementary structures of Si IMPATT diodes

Computer simulation results show that optimum dc to RF conversion efficiency is in descending order for Schottky-barrier GaAs, p⁺-n Si, and n⁺-p Si IMPATT diodes.     

n+-p-p+structure InP solar cells grown by organometallic vapor-phase epitaxy

The fabrication of n⁺-p-p⁺InP solar cells by OMVPE has been studied. A conversion efficiency (active area) as high as 20 percent under AM1.5 illumination has been obtained. It is experimentally verified that the n⁺-p-p⁺InP solar cell has a higher resistance to radiation degradation than the n⁺-p InP solar cell. Diode characteristics and photovoltaic performances such as saturation current density, diode-ideality factor, and open-circuit voltage for the n⁺-p-p⁺cells are found to drastically deteriorate when junction depth decreases to ≤ 0.15 µm. An electron concentration dependence of a hole diffusion length in n-InP is estimated from the measurement of photoluminescence spectra. For the improvement of photovoltaic performances, a series of systematic examinations has been made on the relationship between collection efficiency and hole diffusion length from photogenerated carrier distribution analysis.     

Theory of Noise and Transfer Properties of IMPATT Diode Amplifiers

A theory is formulated which describes quantitatively the noise and transfer properties of IMPATT diode reflection-type negative resistance amplifiers. This theory is based on the method used in the large-signal theory of noise in IMPATT diode oscillators by the present authors. The theory takes into account the signal dependence of the noise generation in the diode, the noise and/or modulation present in the input signal, and also the intermodulation effects occurring between the various frequency bands. The equations are conveniently arranged in matrix form; such a formulation makes it easier to obtain quantitative results in terms of measurable noise and modulation parameters. Agreement between measured and theoretically predicted AM and FM noise of injection-locked oscillators is good. The usefulness of the theory is illustrated by results of calculations on minimum attainable noise of a given amplifier, maximum noise allowable on the input signal, AM-FM conversion, phase distortion, bias modulation, and the correlation between various types of noise.     

A Two-Stage IMPATT-Diode Amplifier

The system aspects and packaging of a two-stage FM IMPATT-diode amplifier are described. The amplifier combines the output power of 4 IMPATT diodes in the final stage to provide an output power of greater than 4 W at 6 GHz. The system has a locking bandwidth of greater than 200 MHz with a 16-dB gain and a noise figure of less than 50 dB. Both the design and the experimental performance of the amplifier and each of its stages are discussed. The noise characterization of IMPATT-diode amplifiers, operating as injection-locked oscillators or stable amplifiers, determined the mode of operation for each stage. Included in the paper are experimental results of large-signal noise characterization of both Si and GaAs IMPATT diodes, as are the noise characteristics related to the output power and gain.     

Spectral response limitation mechanisms of a shallow junction n+-p photodiode

Modulated monochromatic visible light at various wavelengths was used to generate photocurrent in a silicon n⁺-p diffused diode. A numerical model which includes electric field, heavy doping bandgap reduction, and doping level mobility dependence was used with fitting techniques to determine the carrier lifetime in the n⁺-region at each wavelength. From these measurements it was concluded that the physical mechanisms involved in limiting the spectral response of the n⁺-p photodiode at short wavelengths (0.42 µm) is due to heavy recombination of photogenerated carriers in the n⁺-region. The latter is caused by the heavy doping which results in a fraction of a nanosecond minority carrier lifetime and a retarding or reduced electric field in the n⁺-region. Surface recombination velocity has little influence on this loss mechanism.     

Nonequilibrium behavior of depletion, inversion, and accumulation grain boundaries

The recombination velocity of polysilicon grain boundaries is calculated from the Shocley-Read-Hall formula, taking into account the balance of charges for nonequilibrium conditions. The calculation is not restricted to grain boundaries in depletion, but applies to the full range of band bending. The results show the existence of significant differences in the nonequilibrium behavior of depletion, inversion, and accumulation grain boundaries. For depletion/inversion grain boundaries, the recombination velocity is small and nearly independent of excitation for both low- and high-state densities, whereas medium-state densities show high recombination velocities and a strong injection dependence. Accumulation grain boundaries always provide lower recombination velocities than depletion/inversion grain boundaries and they do not show any dependence upon excitation. In order to verify the theoretical excitation dependences, several n⁺-p and p⁺-n solar cells prepared from polycrystalline bulk material have been investigated under various insolation conditions. For the n⁺-p cells, deviations from a linear dependence of the short circuit current upon intensity were observed, whereas the p⁺-n cells showed a precisely linear dependence, indicating depletion/inversion grain boundaries in p-type, but accumulation grain boundaries in n-type polysilicon.     

Mo- and Ti-silicided low-resistance shallow junctions formed using the ion implantation through metal technique

Mo-and Ti-silicided junctions were formed using the ITM technique, which consists of ion implantation through metal (ITM) to induce metal-Si interface mixing and subsequent thermal annealing. Double ion implantation, using nondopant ions (Si or Ar) implantation for the metal-Si interface mixing and dopant ion (As or B) implantation for doping, has resulted in ultrashallow ( ≤ 0.1-µm) p⁺-n or n⁺-p junctions with ∼30-Ω sheet resistance for Mo-silicided junctions and ∼5.5-Ω sheet resistance for Ti-silicided junctions. The leakage current levels for the Mo-silicided n⁺-p junctions (0.1-µm junction depth) and the Mo-silicided p⁺-n junction (0.16-µm junction depth) are comparable to that for unsilicided n⁺-p junction with greater junction depth ( ∼0.25 µm).     

Formation of 0.05-μm p+-n and n+-pjunctions by very low (<500 eV) ion implantation

The current-voltage (I-V) characteristics of ultrashallow p⁺ -n and n⁺-p diodes, obtained using very-low-energy (<500-eV) implantation of B and As, are presented. the p⁺-n junctions were formed by implanting B⁺ ions into n-type Si (100) at 200 eV and at a dose of 6×10¹⁴ cm^-2, and n⁺-p junctions were obtained by implanting As⁺ ions into p-type (100) Si at 500 eV and at a dose 4×10¹² cm^-2. A rapid thermal annealing (RTA) of 800°C/10 s was performed before I-V measurements. Using secondary ion mass spectrometry (SIMS) on samples in-situ capped with a 20-nm ²⁸Si isotopic layer grown by a low-energy (40 eV) ion-beam deposition (IBD) technique, the depth profiles of these junctions were estimated to be 40 and 20 nm for p⁺-n and n⁺-p junctions, respectively. These are the shallowest junctions reported in the literature. The results show that these diodes exhibit excellent I-V characteristics, with ideality factor of 1.1 and a reverse bias leakage current at -6 V of 8×10^-12 and 2×10^-11 A for p⁺-n and n⁺-p diodes, respectively, using a junction area of 1.96×10^-3 cm²     

Optimization of the germanium preamorphization conditions forshallow-junction formation

Shallow p⁺-n and n⁺-p junctions were formed in germanium preamorphized Si substrates. Germanium implantation was carried out over the energy range of 50-125 keV and at doses from 3×10¹⁴ to 1×10¹⁵ cm^-2. p ⁺-n junctions were formed by 10-keV boron implantation at a dose of 1×10¹⁵ cm^-2. Arsenic was implanted at 50 keV at a dose of 5×10¹⁵ cm^-2 to form the n⁺-p junctions. Rapid thermal annealing was used for dopant activation and damage removal. Ge, B, and As distribution profiles were measured by secondary ion mass spectroscopy. Rutherford backscattering spectrometry was used to study the dependence of the amorphous layer formation on the energy and dose of germanium ion implantation. Cross-sectional transmission electron microscopy was used to study the residual defects formed due to preamorphization. Complete elimination of the residual end-of-range damage was achieved in samples preamorphized by 50-keV/1×10¹⁵ cm^-2 germanium implantation. Areal and peripheral leakage current densities of the junctions were studied as a function of germanium implantation parameters. The results show that high-quality p⁺-n and n⁺-p junctions can be formed in germanium preamorphized substrates if the preamorphization conditions are optimized     

Subquarter-micrometer gate-length p-channel and n-channel MOSFETswith extremely shallow source-drain junctions

The fabrication of p-channel and n-channel MOSFETs with sub-quarter-micrometer n⁺ polysilicon gates, have been fabricated using extremely shallow source-drain (S-D) junctions, is reported p⁺-n junctions as shallow as 80 nm have been fabricated using preamorphization low-energy BF₂ ion implantation and rapid thermal annealing, and 80-nm n⁺-p junctions have been fabricated using low-energy arsenic ion implantation and rapid thermal annealing. n-channel MOSFETs with 80-mm S-D junctions and 0.16-μm gate lengths have been fabricated, and a maximum transconductance of 400 mS/mm has been obtained. 51-stage n-channel enhancement-mode/enhancement-mode (E/E) ring oscillators and p-channel E/E ring oscillators with extremely shallow S-D junctions have also been obtained     

DC electroluminescence in novel n-p Si/ZnS:Mn heterostructures

The behavior of a novel n⁺-p Si/ZnS : Mn/ITO light-emitting structure capable of limiting the device current during luminescence is described. In contrast with the very strong dependence of current on voltage observed during luminescence in conventional thin-film ZnS electroluminescent structures, the present structure exhibits a pronounced "knee" or reduction in the rate of growth of current with voltage, which coincides with the onset of electroluminescence. Typically, a decay in brightness of < 5 percent is observed after twelve-hours continuous operation when operating at ∼ 15 ft. L using 0.3-percent duty cycle, 20-µs wide dc pulses.     

A current-generating BSF silicon solar cell fabricated through masked ion implantation

A preferentially current-generating back-surface-field (BSF) silicon solar cell with a near-ideal value of the short-circuit current density JSCunder AM1 conditions has been developed through masked ion implantation of the n⁺-p junction. The BSF cells, fabricated in industrial conditions, possess a conversion efficiency η and a fill-factor FF up to 14.2 and 76.8 percent, respectively. The dependence of JSC, η, and FF on technological parameters are outlined in this letter.     

Experimental Evaluation of Noise Parameters in Gunn and Avalanche Oscillators

Equations are presented that express noise-to-carrier ratio and rms frequency deviation of a negative-resistance oscillator with a multiple-resonant circuit in terms of effective available noise power densities of both 1/f and white-noise sources, an effective saturation factor, and an appropriate Q/sub L/ of the oscillator. Experimental evaluation of the noise parameters in Gunn and avalanche oscillators by use of these equations is described. AM and FM noise measurements have been made on X-band Gunn oscillators and Si and GaAs avalanche oscillators for frequency off carriers extending from 1 kHz to 10 MHz. Both 1/f and white noise have been observed in these oscillators. The validity of the above equations has been verified for Gunn oscillators from the dependence of the noise spectra on Q/sub L/. For Gunn oscillators and Si and GaAs avalanche oscillators, the effective noise-temperature ratio for white noise, N/kT/sub 0/, has been found to be 23~29, 41~51, and 38~44 dB, and the effective saturation factor to be 2~2.9, 0.5~2.4, and 2, respectively. An increase of N/kT/sub 0/ with the RF voltage across the diode has been observed in Si avalanche oscillators. Parameters for 1/f noise have also been evaluated approximately.     

Bulk defect induced low-frequency noise in n+-p silicondiodes

The low-frequency 1/f-like noise of gated n⁺-p silicon diodes has been measured and analyzed in terms of trapping and detrapping of holes in defect centers located in the bulk section of the space charge region at 0.43 eV below the conduction band. Both the trap characteristics and their precise physical location are resolved from the noise measurements showing that the noise producing defect region moves closer to the metallurgical junction when forward bias is increased. The noise measurements independently confirm that thermal substrate pretreatments lower the defect density in the diodes fabricated in Czochralski (CZ) grown substrates. The defect centers are assumed to be associated with precipitated oxygen/dislocation complexes     

A New Look at Noise in Transferred Electron Oscillators

Low-frequency current and voltage fluctuations have been measured, and it has been confirmed that noise in packaged transferred electron devices (TED's) is due to three distinct noise mechanisms: flicker, generation-recombination, antd thermal noise. For transferred electron oscillators (TEO's), this low-frequency noise is upconverted into the microwave frequency range and adds to the intrinsic RF noise. We have found that between 1 kHz and 1 MHz off the carrier, temperature-dependent generation-recombination noise is the main contributor to the total noise. A model of a noisy TEO is presented. This model permits the calculation of AM and FM noise spectra from device and circuit parameters for measured low-frequency noise or the derivation of device characteristics from noise and circuit parameter measurements.     

Avalanche region width in various structures of IMPATT diodes

The avalanche region of one-sided and two-sided abrupt junctions has been studied. These are the structures most commonly utilized for IMPATT diodes. Numerical results are presented which show that n⁺-p Si diodes have much narrower avalanche regions, due to the unequal ionization rates in Si, than the complementary p⁺-n type. The implications of these results with respect to IMPATT diode design are discussed.     

Spectral response of n+-n-p and n+-p photodiodes

Results of calculations for the quantum efficiency of three different types of n⁺-p, n⁺-n-p, and OCI-HLE diodes are reported. Exact numerical modeling of current density equations, modified to include bandgap reduction and Auger recombination is used to compute the quantum efficiency of these diodes. It is found that an optimized n⁺-p structure can result in over all spectral response comparable to the n⁺-n-p structure, although it is not as good as that of the OCI-HLE type of diodes. Further, these calculations show that one can achieve low dark current in these diodes, but at the expense of lower quantum efficiency particularly for wavelengths less than 0.4 µm.