Generation of powerful microwave voltage oscillations in a diffused silicon diode

The mechanism of the generation of powerful microwave voltage oscillations in a diffused silicon diode is studied. A reverse current 2 kA in amplitude is passed through a 0.5-cm² diode with a structure thickness of 320 μm, a p-n junction depth of 220 μm. At an average diode voltage of ～300 V and a microwave pulse duration of ～200 ns, the maximum voltage swing reaches 480 V. The oscillation frequency lies in the range 5 to 7 GHz; the power of the microwave pulse component is ～300 kW. A theoretical consideration shows that voltage oscillations are caused by periodically repeating processes of breakdown and structure filling with plasma followed by its removal by the reverse current. The frequency and voltage swing are controlled by the current density and dopant-concentration gradient in the vicinity of the p-n junction.     

Electron transport in silicon carbide natural superlattices under the Wannier-Stark quantization conditions: Basic issues and application prospects

Hot-electron transport in silicon carbide natural superlattices was investigated. Almost all of the theoretically predicted effects related to the Wannier-Stark localization, such as Bloch oscillations, Stark-phonon resonances, miniband-state localization, and resonance tunneling between the minibands, were observed for the first time. In n ⁺-n ^?-n ⁺ structures optimized for the measurements at microwave frequencies, the formation of the mobile electric domain was observed in the electric-field range corresponding to the Bloch oscillation conditions; thus, the onset of the microwave oscillations in the 6H-SiC natural superlattice can be stated with a high degree of confidence.     

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.     

Current dependence of capacitance of germanium p +-p junctions in the temperature range of 290–330 K

The current dependence of differential capacitance of germanium p ⁺-p junctions with the p-region resistivity of 45, 30, and 10 Ω cm is investigated in the temperature range of 290–350 K. It is shown that the current dependence of the p ⁺-p-junction capacitance varies with an increasing junction temperature. At the temperature of 290 K, the capacitance decreases with an increasing reverse current, changes sign from positive to negative, and increases with the forward current. At 330 K, the capacitance decreases to the lowest positive value with an increasing reverse current and changes sign to negative with increasing the forward current. At 310 K, the p ⁺-p-junction capacitance can change the sign from positive to negative with increasing the forward and reverse current. It is assumed that the positive and negative p ⁺-p-junction capacitance is caused by the change in the junction-region charge by the external voltage.     

Subnanosecond 4<Emphasis Type="Italic">H</Emphasis>-SiC diode current breakers

Mesa epitaxial 4H-SiC-based p ⁺-p-n ₀-n ⁺ diodes have been fabricated and their reverse recovery characteristics have been measured in modes typical of fast semiconductor current breakers, drift step recovery diodes, and SOS diodes. It has been found that, after the short (～10 ns) pulsed injection of nonequilibrium carriers by a forward current with a density of 200–400 A cm^?2 and the subsequent application of a reverse voltage pulse (with a rise time of 2 ns), diodes can break a reverse current with a density of 5–40 kA cm^?2 in a time of about (or less than) 0.3 ns. A possible mechanism for ultrafast current breaking is discussed.     

A low-high-junction solar-cell model developed for use in tandem cell analysis

A comprehensive low-high (L-H) junction solar cell model has been developed. It accounts for actual solar spectrum related photogeneration of carriers in all regions of the n-p-p⁺ cell and allows for any value of rear surface-recombination-velocity (SRV). In typical GaAs L-H junction solar cells, photogeneration in the p⁺ region, but not the p region, is found to be negligible. The L-H junction's space-charge-layer recombination current density is also negligible. Assigning a non-infinite value of rear surface SRV makes this model applicable to tandem multi-junction structures made from materials with different band gaps.     

Violation of neutrality and occurrence of S-shaped current-voltage characteristic for doped semiconductors under double injection

It is shown that violation of quasi-neutrality and its subsequent recovery (with an increase in the current density) may occur in doped n layers of p ⁺-n-n ⁺ structures under double injection at a high injection level and for a certain combination of electrical parameters. The violation of quasi-neutrality leads to a significant increase in the voltage across the base and subsequent recovery of neutrality gives rise to sharp decrease in voltage drop, as a result of which an S-shaped current-voltage characteristic is formed. The characteristic threshold current density for this effect is proportional to the base doping level N _d .     

Impact-ionization wave breakdown and generation of picosecond pulses in the ultrahigh-frequency band in GaAs drift step-recovery diodes

It is shown experimentally for the first time that the operation of GaAs drift step-recovery diodes produced on the basis of p⁺-p⁰-n⁰-n⁺ is accompanied by the generation of ultrahigh-frequency oscillations in the form of trains of short pulses with a duration of ～10 ps. The amplitude and repetition frequency of these pulses are as high as ～100 V and ～(10–100) GHz, respectively. The phenomena of delayed reversible wave breakdown and excitation of ultrahigh-frequency oscillations in the structures of GaAs step-recovery diodes are found to open up new avenues for progress both in the physics and technology of semiconductor devices based on GaAs structures and in the technology of ultrahigh-frequency systems and devices that deal with pulsed signals of picosecond-scale duration.     

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.     

Negative capacitance (impedance of the inductive type) of silicon p +-n junctions irradiated with fast electrons

Silicon p ⁺-n junction diodes irradiated with 3.5-MeV electrons (with the dose of 4 × 10¹⁶ cm^?2) are studied. The diodes’ inductance (L) was measured at a frequency f = 1 MHz with the amplitude of alternating current equal to 0.25 mA. Simultaneously with measurements of L at alternating current, a direct current was passed through the forward-biased diode, which brought about the injection of minority charge carriers into the base. In order to identify both of the mechanisms that give rise to the inductive-type impedance in irradiated diodes with the p ⁺-n junction and the main radiation defects that are directly involved in the formation of this impedance, irradiated samples were annealed isochronously in the temperature range T _a = 225–375°C with sub-sequent study of the main characteristics of the defects by deep-level transient spectroscopy. It is shown that the inductive-type impedance in irradiated diodes is caused by the processes of capture and retention of charge carriers injected into the base at the trapping centers for a time ～1/2f, i.e., for a half-period of oscillations. It is also shown that the trapping centers are the vacancy-oxygen complexes introduced by irradiation with electrons.     

Microwave oscillations in pnp reach-through BARITT diodes

Studies have been made on the microwave oscillations of reach-through p⁺np⁺ and related structures operated as BARITT diodes (BARrier Injection Transit Time diodes).The mechanisms responsible for the microwave oscillatins are the exponential increase of the local carrier population at the forward-biased pn junction and the transit-time delay of injected carriers transversing the drift region. The small-signal impedance and noise measure of the device are calculated based on (1) the thermionic injection and the space-charge-limited effects and (2) the separation of the drift region into a low-field region and a saturated-velocity region.Microwave CW oscillatins have been obtained from p⁺np⁺ BARITT diodes made from an epitaxial n on p⁺ silicon substrate with epitaxial layer thickness of 8 μm and doping concentration of 5 × 10¹⁴cm^?3. Microwave CW power of the order of a few milliwatts has been obtained at 7 GHz with efficiency greater than 1 per cent. Good agreement has been obtained between the measured and the calculated small-signal impedances.     

Voltage dependence of the differential capacitance of a p +-n junction

The dependences of the differential capacitance and current of a p ⁺-n junction with a uniformly doped n region on the voltage in the junction region are calculated. The p ⁺-n junction capacitance controls the charge change in the junction region taking into account a change in the electric field of the quasi-neutral n region and a change in its bipolar drift mobility with increasing excess charge-carrier concentration. It is shown that the change in the sign of the p ⁺-n junction capacitance with increasing injection level is caused by a decrease in the bipolar drift mobility as the electron-hole pair concentration in the n region increases. It is shown that the p ⁺-n junction capacitance decreases with increasing reverse voltage and tends to a constant positive value.     

1/f noise in n+-p-n microwave transistors

1/f noise measurements in the base current and the collector current of NEC 57807 n⁺-p-n microwave transistors show that the noise is not of the mobility fluctuation type, since the current dependence of S_IR(f) and S_IC(f) differs from the theoretical predictions. The low collector current 1/f noise makes it doubtful whether the mobility fluctuation concept is applicable in this case.     

Microwave Annealing of High Dose Al<Superscript>+</Superscript>-implanted 4H-SiC: Towards Device Fabrication

High-purity semi-insulating 8° off-axis 〈0001〉 4H-SiC was implanted with Al⁺ at different doses and energies to obtain a dopant concentration in the range of 5 × 10¹⁹–5 × 10²⁰ cm^?3. A custom-made microwave heating system was employed for post-implantation annealing at 2,000 °C for 30 s. Sheet resistance and Hall-effect measurements were performed in the temperature range of 150–700 K. At room temperature, for the highest Al concentration, a minimum resistivity of 3 × 10^?2 Ω cm was obtained, whereas for the lowest Al concentration, the measured resistivity value was 4 × 10^?1 Ω cm. The onset of impurity band conduction was observed at around room temperature for the samples implanted with Al concentrations ≥3 × 10²⁰ cm^?3. Vertical p ⁺-i-n diodes whose anodes were made by 1.5 × 10²⁰ cm^?3 Al⁺ implantation and 2,000 °C/30 s microwave annealing showed exponential forward current–voltage characteristics with two different ideality factors under low current injection. A crossover point of the temperature coefficient of the diode resistance, from negative to positive values, was observed when the forward current entered the ohmic regime.     

Spectral response of an injection-mode infrared detector

Large injection pulses are observed in simple circuits containing forward-biased silicon p-i-n (p⁺-n-n⁺) structures at liquid helium temperatures. The pulse rate is dependent on the intensity of infrared radiation incident on the device. The substantial voltage, current, and power output eliminates the need for on-chip or off-chip amplifiers. The first observation of the spectral response of such a detector as measured from 22 to 32 μm with a liquid-helium-cooled monochromator is reported. The response is similar to other extrinsic detectors and modulated by a multiple internal reflection interference pattern. The interference pattern and the origin of optical absorption are analyzed.     

Solution of the problem of charge-carrier injection into an insulating layer under self-consistent boundary conditions at contacts

The problem of charge carrier injection into a finite-length insulating layer is analytically solved in the drift-diffusion approximation, taking into account self-consistent boundary conditions. The main assumption is the neglect of intrinsic doping of the i-type layer. The solution allows calculation of the potential, electric field, and current-voltage characteristics of various structures, i.e., metal-i-n ⁺ (or p ⁺)-semiconductor, metal-i-layer-metal, and n ⁺(p ⁺)-i-n ⁺(p ⁺) structures. The solution allows generalization for structures having heterobarriers at semiconductor layer interfaces. The proposed approach considers contact phenomena and volume effects associated with the space-charge-limited current in the i-type layer. The solution is valid in both extreme cases and intermediate conditions.     

Effect of double reflection on the forward current-voltage characteristics of a silicon p+-s-n+ epitaxial diode

The behaviour of both majority and minority carriers in a p⁺-s-n⁺ epitaxial diode (where s may be p or n) has been investigated in this paper. Forward current-voltage characteristics of the diodes are obtained by exact numerical analysis, taking into account the effects of energy-gap narrowing, Auger recombination and carrier-carrier scattering. As with previous authors, it is found that the forward current increases with increasing middle layer thickness. The present analysis shows that such increase occurs only upto a specific applied bias, after which the forward current decreases with increasing middle layer thickness. This behaviour is attributed to double reflection, i.e. the reflection of both majority and minority carriers by the p-n junction and high-low junction respectively. Beyond the specific bias so determined, junction reflection loses its effectiveness. Distribution of carrier concentration and junction voltages for several device configurations are given to illustrate these features. The majority carrier reflection by the p-n junction is found to have a dominating effect in all cases.     

Degradation mechanism for silicon p+-n junctions under forward bias

Leakage current degradation has been observed during forward bias stressing of silicon integrated p⁺-n junctions. Detailed characterization results of the anomalous leakage behavior are discussed in this paper. From these results an electric field-enhanced impurity diffusion mechanism has been proposed to explain both the strong temperature and forward bias dependencies on leakage current time-to-saturation. An activation energy has been determined for this mechanism (0.48±0.04 eV) and is in good agreement with that previously determined for diffusion of interstitial copper in p-type silicon. Subsequent Secondary Ion Mass Spectrometer elemental analysis has confirmed the presence of copper near the surface of the epitaxial layer containing the p⁺-n device.     

Profiling the boron distribution in asymmetric n +-p silicon photodiodes and a new concept for creating selectively sensitive photocells for megapixel color-image receivers

The spectral photosensitivity of n ⁺-p silicon photodiodes with a p ⁺ layer implanted in the substrate is studied experimentally. It is demonstrated that such p ⁺ doping effectively shifts the long-wavelength edge of the photosensitivity in the optical spectral range and the shift depends on the depth of the p ⁺ layer. A new concept for creating selectively sensitive photocells for megapixel color-image receivers is proposed. The receivers are based on n ⁺-p photodiode structures containing a few layers that are implanted at different depths and form desired color-separating potential barriers and lateral diffusion channels for collection of the minority carriers generated by photons of different colors.