Graphite/<Emphasis Type="Italic">p</Emphasis>-SiC Schottky Diodes Prepared by Transferring Drawn Graphite Films onto SiC

Graphite/p-SiC Schottky diodes are fabricated using the recently suggested technique of transferring drawn graphite films onto p-SiC single-crystal substrates. The current–voltage and capacitance–voltage characteristics are measured at different temperatures and at different frequencies of a small-signal AC signal, respectively. The temperature dependences of the potential-barrier height and of the series resistance of the graphite/p-SiC junctions are measured and analyzed. The dominant mechanisms of the charge–carrier transport through the diodes are determined. It is shown that the dominant mechanisms of the transport of charge carriers through the graphite/p-Si Schottky diodes at a forward bias are multi-step tunneling recombination and tunneling described by the Newman formula (at high bias voltages). At reverse biases, the dominant mechanisms of charge transport are the Frenkel–Poole emission and tunneling. It is shown that the graphite/p-SiC Schottky diodes can be used as detectors of ultraviolet radiation since they have the open-circuit voltage V_oc = 1.84 V and the short-circuit current density I_sc = 2.9 mA/cm² under illumination from a DRL 250-3 mercury–quartz lamp located 3 cm from the sample.     

Schottky barrier height modification in Au/n-type 6H-SiC structures by PbS interfacial layer

We have prepared the Au/PbS/n-6H-SiC Schottky diodes with interface layer and the reference Au/n-6H-SiC/Ni Schottky diodes without interface layer to realize Schottky barrier height (SBH) modification in the Au/SiC Schottky diodes. The BH reduction has been succeeded by the PbS interlayer to modify the effective BH by influencing the space charge region of the SiC. The PbS thin layer on the SiC was formed by the vacuum evaporation. The SBH values of 0.97 and 0.89 eV for the samples with and without the interfacial PbS layer were obtained from the forward bias current-voltage (I-V) characteristics. X-ray diffraction (XRD) study was carried out to determine the structural formation of the PbS on SiC. The reduction of the BH in the Au/PbS/n-6H-SiC Schottky diodes has been attributed to the fact that the interface states have a net positive interface charge in metal/n-type semiconductor contact, and thus the positive space charge Q_sc in the Au/PbS/n-6H-SiC Schottky diodes becomes smaller than if the interface state charges Q_ss were absent. The experimental carrier concentration value of 4.73 × 10¹⁷ cm⁻³ obtained from the forward and reverse bias capacitance-voltage characteristics for the Au/PbS/n-6H-SiC contacts is lower than the value of 5.52 × 10¹⁷ cm⁻³ obtained for the reference diode, and this is an evidence of the reduction of the BH by the modification of the space charge density of the SiC.     

Electrical properties of MOS diodes In/TiO2/p-CdTe

In/TiO₂/p-CdTe MOS diodes, which have a rectification coefficient of K = 6 × 10³ at an external bias of 2 V, are fabricated for the first time by means of the inexpensive spray-pyrolysis method. It is established that tunnel-recombination processes in the MOS structures under investigation for forward and reverse voltages with the participation of levels at an energy depth of 0.25 eV are the dominant current-flow mechanism. The features of the voltage-capacitance characteristics of In/TiO₂/p-CdTe MOS diodes testify to a sharp decrease in the resistance of the TiO₂ high-resistance layer at forward bias, which is caused by the relation between the energy parameters of components of the MOS structure under investigation.     

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.     

Small-signal conductance vs temperature: A rapid means of determining the nature of current transport in high-doped n-GaAs Schottky barrier diodes

Measurements of small-signal forward conductance vs temperature at a constant bias current, and the reverse conductance vs temperature at a constant bias voltage have been carried out on ion-implanted n-GaAs Schottky barrier diodes fabricated on semi-insulated substrates, for the temperature range of 97–340 K. The results obtained have been interpreted in terms of diode ideality factors and compared with those calculated using the thermionic field emission model for the forward bias case and the pure field emission model for the reverse bias case.     

High performance n/p and p/n germanium diodes at low-temperature activation annealing

In this work we demonstrate the fabrication and characterization of high performance junction diodes using annealing temperatures within the temperature range of 300-350 °C. The low temperature dopant activation was assisted by a 50 nm platinum layer which transforms into platinum germanide during annealing. The fabricated diodes exhibited high forward currents, in excess of 400 A/cm² at ∼|0.7| V for both p⁺/n and n⁺/p diodes, with forward to reverse ratio I_F/I_R greater than 10⁴. Best results for the n⁺/p junctions were obtained at the lower annealing temperature of 300 °C. These characteristics compare favorably with the results of either conventional or with Ni or Co assisted dopant activation annealing. The low-temperature annealing in combination with the high forward currents at low bias makes this method suitable for high performance/low operating power applications, utilizing thus high mobility germanium substrates.     

A dynamic model of the p-n-n+ step recovery diodes for the numerical analysis of pulse circuits

A new p-n-n⁺ diode model for circuit transient analysis is developed. In contrast to existing circuit models, this model reflects all step-recovery diode (SRD) effects during switching on and off, including “ramp” of slow recovery phase. It is accomplished by taking into account the dynamic physical phenomena in the p-n-n⁺ diodes when switched. A non-linear dynamic diffusion capacitance of the diode model is determined by the dependence of the instantaneous base charge on the instantaneous diode voltage.The accuracy of the presented model is verified by comparison of the calculated and measured wave forms of some pulse circuits.The present model has been proved to be more accurate than SRD models previously published.     

A study of deep centers in microplasma channels in GaP light-emitting diodes with green-emission spectrum

The statistical delay of microplasma breakdown in GaP light-emitting diodes with the green-emission spectrum is studied. The unusual profound effect of deep centers on the statistical delay of avalanche breakdown is observed in the temperature range of 300–380 K; this effect is caused by a variation in the charge state of these centers due to a reduction in the reverse bias applied to the p–n junction. Four deep levels are revealed and their parameters are determined.     

Interface state density in Au-nGaAs Schottky diodes

A method for determining the surface state density in Schottky diodes taking into account both I–V and C–V data while considering the presence of a deep donor level is presented. The model assumes that the barrier height is controlled by the energy distribution of surface states in equilibrium with the metal and the applied potential and does not include, explicitly, an interfacial layer. The model was applied to extract interface state densities of Au-nGaAs guarded Schottky diodes fabricated from bulk and VPE (100) GaAs with carrier conentrations between 3 × 10¹⁵ and 8 × 10¹⁶ cm^?3. These diodes exhibited ideality (n) factors of approximately 1.02 and room temperature saturation current densities ～10^?8 A/cm². This model is in substantial agreement with forward bias measurements over the 77–360°K temperature range investigated, in that a temperature-independent energy distribution of interface states was obtained. In reverse bias the interface state model is most valid with the higher carrier concentration material and at high temperature and low bias voltage. Typical interface state densities from 0.07 eV above the zero bias Fermi level to 0.01 eV below the Fermi level were 2 × 10¹³ cm^?2 eV^?1. The validity of the model under reverse bias is restricted by a non-thermionic reverse current, thought to be enhance field emission from traps.     

Planar,ion-implanted bipolar devices in GaAs

Selected-area ion implantation using heavy metal masks to define the device geometry has been used to fabricate doubly implanted npn bipolar transistors and planar, isolated pn junction devices in GaAs. The bipolar transistors exhibited common-emitter current gains as high as 25. Collector-base breakdown voltages of 45 V were observed. The junction diodes (～200 um dia.) exhibited sub-nanoampere leakage currents at 15 V of reverse bias. Surface leakage appears to be the dominant mechanism responsible for the observed leakage currents. The diode forward current is limited by recomination in the space charge region.     

Modelling of semiconductor diodes made of high defect concentration,irradiated, high resistivity and semi-insulating material: The capacitance–voltage characteristics

Full modelling is reported of the capacitance of a long PIN semiconductor diode with a high concentration of generation–recombination (g–r) centres and different concentrations of deep traps. There are considerable differences from the textbook results given for normal lifetime diodes which have low concentrations of g–r centres. For a low density of g–r centres, the capacitance is the usual value. That is it decreases as V^−1/2 with increasing reverse bias while it increases rapidly with increasing forward bias. For high density of g–r centres and in reverse bias a departure from this voltage dependence is observed, while in forward bias a negative capacitance appears. This agrees with experiment. From these results we present a physical understanding of the processes involved. There are specific applications of these results to radiation damaged devices, lifetime killed diodes and devices made from high resistance and semi-insulating materials, especially in the interpretation of the C–V curves to evaluate the fixed space charge density.     

A computer-aided simulation model for the I–V characteristic of M-n-p silicon Schottky-barrier diodes produced by use of low-energy arsenic-ion implantation

Current-transport properties of Al-n-p silicon Schottky-barrier diodes have been studied both experimentally and theoretically. An analytical model for the I-V characteristic of a metal-n-p Schottky barrier diode has been developed by using an interfacial layer-thermionic-diffusion model. Assuming a Gaussian distribution for the implanted profile, the barrier-height enhancement and ideality factor have been derived analytically. Using low energy (25 KeV) arsenic implantation with the dose ranged form 8 × 10¹⁰/cm² to 10¹²/cm², Al-n-p silicon Schottky barrier diodes have been fabricated and characterized. Comparisons between the experimental measurements and the results of computer simulations have been performed and satisfactory agreements between these comparisons have been obtained. The reverse I–V characteristics of the fabricated Al-n-p silicon Schottky barrier diodes can also be well simulated by the developed model.     

Numerical modeling of looped C-V Characteristics in Ap+n junction containing mid-bandgap electron traps

The capacitance of p⁺n junctions containing traps or deep centers depends on the time variation of the applied reverse voltage. Capacitance changes results from the time dependent variation of the density of traps filled with electrons within the depletion region. If a cyclical reverse voltage in applied to the junction, capacitance hysteresis due to the time-dependent charge variation within the depletion region should be observed. The hysteresis loops, as a function of the bias drive rate, temperature, and total concentration of traps provide some information on the characteristics of the traps.This paper presents a numerical analysis of looped C-V characteristics in a p⁺n junction containing midbandgap electron traps and also discusses the variation of loops as a function of the bias drive rate, dV/dt, total concentration of traps, N_T, and emission rates of electrons and holes, e_n and e_p, based on our numerical modeling.     

Capacitance-voltage characteristics of p-n structures based on (111)Si doped with erbium and oxygen

Capacitance-voltage characteristics of tunneling diodes fabricated by co-implantation of erbium and oxygen in single-crystal (111)Si wafers have been studied. Anomalous enhancement of the p-n-junction capacitance with increasing reverse bias has been observed at certain temperatures depending on the implantation dose. The rise in capacitance (decrease in the space charge region width) is associated with the formation of deep levels of high density in the band gap of n-layer of the p-n junction and electron emission from these levels in the space charge region with increasing voltage. The obtained results show that the parameters of the defects responsible for the levels depend on the erbium and oxygen implantation doses.     

Properties of the contact on ion cleaned n and p type silicon surfaces

Schottky contacts were produced by silver evaporation on Si(100) surfaces cleaned by ion sputtering and partial annealing. The samples work function were measured before and after metal deposition with the Kelvin method, in an experimental set-up which allowed a topografical study and direct comparison between n and p types. Clean surfaces with and without a residual layer of oxide was achieved and controlled by AES. It was found that the Fermi level of all the surfaces was pinned by donor states created by the bombardment and that there was no barrier on n type and an important surface barrier on p type. The diodes we obtained presented no barrier on n type and a rectifying contact on p type. So we deduced that the Schottky barrier is already fully formed before metal contact is achieved. Furthermore study of the electrical properties of the diodes had shown that the bombardment creates donor states responsible for the barrier and a perturbated layer with deep acceptor traps responsible for the current flow mechanism. A residual layer of oxide and a post annealing of the device did not noticeably change the Schottky barrier in the diodes achieved on p type but led to clearly differenciated performances for the diodes achieved on both p and n type substrate. So we therefore concluded that the characteristics of the deep acceptor traps of the superfacial layer are modified by the oxide and annealing, both of which on the other hand having no effect on the surface donor states.     

Electrical properties of anisotype heterojunctions n-CdZnO/p-CdTe

Anisotype surface-barrier n-Cd_0.5Zn_0.5O/p-CdTe heterojunctions are fabricated by the high-frequency sputtering of a Cd_0.5Zn_0.5O alloy film onto a freshly cleaved single-crystal CdTe surface. The main electrical properties of the heterojunctions are studied and the dominant mechanisms of charge transport are established, namely, the multistage tunnel-recombination mechanism under forward bias, Frenkel-Pool emission, and tunneling under forward bias. The influence of the surface electrically active states at the heterojunction interface is analyzed and their surface concentration is evaluated: N _ss ?? 10¹⁴ cm^?2.     

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.     

Impedance and barrier capacitance of silicon diodes implanted with high-energy Xe ions

Characteristics of Si p⁺n diodes with non-uniformly distributed compensating defects, which were introduced by implantation with Xe²³⁺ ions, have been studied. The layer with the maximum concentration of the compensating defects was located in the vicinity of the metallurgical p-n junction. It is found that the presence of the defect layer results in non-monotonic dependences of the imaginary part of impedance (−Z″) and differential conductance (G = −dI/dU) of the implanted diodes on reverse bias voltage U. An equivalent circuit of the irradiated diode is proposed, which allows us to approximate the measured frequency dependences of capacitance and conductance of the irradiated diodes and to determine values of diode barrier capacitance C_pn at different reverse bias voltages.     

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.     

The small signal admittance of carbon implanted p-n diodes

In this paper we consider, in detail, how the introduction of radiation damage centres, produced by the implanation of carbon ions, affects the small signal admittance of silicon p-n diodes. Thermally stimulated capacitance measurements are used to obtain the charge states and activation energies of the damage centres. For carbon doses between 1 × 10¹¹ cm^?2 and 1 × 10¹² cm^?2 two trapping levels are observed with activation energies of E_t?E_v=0·31 eV and E_c?E_t=0·37 eV, and for doses between 5 × 10¹² cm^?2 and 5 × 10¹³ cm^?2 an extra level appears with an energy of E_c?E_t=0·25 eV. A study is made of the effects of these damage centres on the small signal capacitance and conductance of the diodes under forward bias. The results are interpreted in terms of a conductivity modulation effect, and it is proposed that this technique yields valuable information on the profile of the damage centres.