Radiation hardness of SiC ion detectors under relativistic protons

Schottky diodes based on 6H-SiC epitaxial films exposed to 1000 MeV protons at a dose of 3×10¹⁴ cm^?2 have been studied by precision alpha spectrometry. Parameters of deep levels introduced by protons were determined by deep-level transient spectroscopy. The number of vacancies generated in proton tracks was found using TRIM software. The width of the space charge region and the hole diffusion length before and after irradiation were obtained by processing the alpha-spectrometry and capacitance measurements. Minor variations in the charge transport properties of epitaxial 6H-SiC detectors were observed.     

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.     

Observation of minority-carrier traps in Schottky diodes with a high barrier and a compensated near-contact region using deep-level transient spectroscopy

Schottky diodes based on the single-crystal n-ZnSe and fabricated by nitrogen-ion implantation with subsequent postimplantation treatment employing radical-beam epitaxy in atomic oxygen were studied using deep-level transient spectroscopy. On the assumption that the Schottky barrier is high and the near-contact region is compensated, the processes resulting in the occurrence of traps of minority charge carriers under negative biases were analyzed. The procedure for determining the compensated region thickness and the concentration of minority charge carriers in this region is described. The mechanisms of defect formation in zinc selenide crystals under annealing in atomic oxygen are described on the basis of the deep-level transient spectroscopy results.     

Optical and electrical properties of 4<Emphasis Type="Italic">H</Emphasis>-SiC irradiated with fast neutrons and high-energy heavy ions

Photoluminescence and deep-level transient spectroscopy are used to study the effect of irradiation with fast neutrons and high-energy Kr (235 MeV) and Bi (710 MeV) ions on the optical and electrical properties of high-resistivity high-purity n-type 4H-SiC epitaxial layers grown by chemical vapor deposition. Electrical characteristics were studied using the barrier structures based on these epitaxial layers: Schottky barriers with Al and Cr contacts and p⁺-n-n⁺ diodes fabricated by Al ion implantation. According to the experimental data obtained, neutrons and high-energy ions give rise to the same defect-related centers. The results show that, even for the extremely high ionization density (34 keV/nm) characteristic of Bi ions, the formation of the defect structure in SiC single crystals is governed by energy losses of particles due to elastic collisions.     

Radiation defects in n-4H-SiC irradiated with 8-MeV protons

Capacitance-related methods and electron spin resonance were used to study the deep-level centers formed in n-4H-SiC as a result of irradiation with 8-MeV protons. For the samples, Schottky diodes and p-n structures formed on the layers either obtained by sublimational epitaxy or produced commercially by CREE Inc. (United States) were used. It was found that the type of centers introduced by irradiation is independent of the technology of the material growth and the type of charged particles. On the basis of the results of annealing the defects and the data of electron spin resonance, the possible structure of the centers is suggested.     

The use of hydrogen passivation to fabricate Schottky diodes for DLTS measurements of heavily-doped p+ Si

Schottky diodes were successfully fabricated on p⁺ Si for deep-level transient spectroscopy (DLTS) measurements by the use of hydrogen passivation of boron. Atomic hydrogen was introduced into the near-surface region of boron-doped (1 0 0) CZ Si crystals, which had a resistivity of about 0.01 Ω cm, at temperatures between room temperature and 300°C by exposure to a hydrogen plasma. Rectifying characteristics were obtained for fabricated Schottky contacts on hydrogenated samples. This was due to the carrier concentration decrease in the near-surface region by hydrogen passivation of boron. As the hydrogenation temperatures were increased, the decrease in carrier concentration was significant. Some results of DLTS measurements were given for fabricated diodes.     

Electrical characteristics of laser-contacted diodes

We have fabricated p⁺-n and Schottky diodes with contacts made of laser-formed palladium-silicide. The electrical characteristics of these diodes are presented. The reverse currents and breakdown voltages are comparable to conventionally contacted p⁺-n diodes. The barrier height of laser-formed Schottky diodes agrees well with published values for Pd₂Si. The promising results point out the potential applications of contact formation by laser irradiation in device manufacture.     

Schottky barriers on InSb

Schottky barriers formed on air-cleaved InSb are found to be more reproducible and have less leakage than diodes fabricated by chemical processing. Etched surfaces yield diodes with large leakage currents and high series resistances whose values are correlated, i. e. , high series re-sistances have less leakage and vice versa. With air-cleaved surfaces the lowest leakage is observed when the surfaces adjoining the contact are covered with SiO₂. From C^-2 versus V data, barrier heights of 50 mV and 175 mV at 77K are measured for Au contacts to n- and p-type InSb, respectively. The current-voltage characteristics of Au contacts are consistent with these barriers, but the low-temperature field-emission behavior appears to be dom-inated by tunneling via traps. For Pb contacts, deep-level traps are in evidence that can lead to erroneous in-terpretations of C^-2 versus V voltage intercepts. The I-V data for Pb contacts suggest V_Bn ≈0 and V_Bp ≈E_g/q. Diodes fabricated on vacuum-cleaved surfaces have large leakage currents which result from the etching procedures introduced to isolate individual diodes.     

Investigation of leakage characteristics of PbSnTes̵bndPbTe inverted heterostructure diodes

The results of a study of the overall electrical characteristics of PbSnTe diodes are presented and interpreted on the basis of a simple p-n junction model. These diodes are made from a PbSnTe epilayer grown by a liquid-phase epitaxy technique on a PbTe wafer substrate. The diodes have a 50% spectral cutoff at 11.5 μm when operated at 85K, which shifts to 14.5 μm at T = 15K. Major contributions to the bulk current are diffusion current at T > 80K, and generation-recombination current for 80 >T ? 30K. Surface related leakage is predominant at T < 30 K for small area diodes (A < 1 × 10^?4 cm²) at low bias voltage. Bulk defect related leakage contributes heavily the large area diodes (A > 1 × 10^?3 cm²) at T ? 60K.     

Electrical characteristics of Pd Schottky contacts on ZnO films

The electrical characteristics of Pd Schottky contacts on ZnO films have been investigated by current-voltage (I–V) and capacitance–voltage (C–V) measurements at different temperatures. ZnO films of two thicknesses (400 nm and 1000 nm) were grown by DC-magnetron sputtering on n-Si substrates. The basic structural, optical and electrical properties of these films are also reported. We compared the two Schottky diodes by means of characteristic parameters, such as rectification ratio, ideality factor (η), barrier height (Φ_b) and series resistance and obtained better results for the 1000 nm-ZnO Schottky diodes. We also discussed the dependence of I‐V characteristics on temperature and the two distinct linear regions observed at low temperatures are attributed to the existence of two different inhomogeneous barrier heights. From I–V plots in a log-log scale we found that the dominant current-transport mechanism at large forward bias is space-charge limited current (SCLC) controlled by the presence of traps within the ZnO bandgap. The existence of such traps (deep states or interface states) is demonstrated by frequency-dependent capacitance and deep-level transient spectroscopy (DLTS) measurements.     

Dynamic strain-sensitive characteristics of the Schottky-barrier diodes under a pulsed uniform pressure

Dynamic strain-gage characteristics of Schottky-barrier diodes of the Au-Si:Ni-Sb type subjected to pulsed uniform pressure in the range of P=(0?5)×10⁸ Pa at a temperature of T=300 K were studied. Studies of I-V characteristics of the diodes showed that, due to an additional temperature effect induced by the pulsed pressure, the dynamic parameters of the stress-sensitivity effect in these diodes were 20–30% larger than the corresponding static parameters.     

Effect of the fabrication conditions of SiGe LEDs on their luminescence and electrical properties

SiGe-based n⁺–p–p⁺ light-emitting diodes (LEDs) with heavily doped layers fabricated by the diffusion (of boron and phosphorus) and CVD (chemical-vapor deposition of polycrystalline silicon layers doped with boron and phosphorus) techniques are studied. The electroluminescence spectra of both kinds of LEDs are identical, but the emission intensity of CVD diodes is ～20 times lower. The reverse and forward currents in the CVD diodes are substantially higher than those in diffusion-grown diodes. The poorer luminescence and electrical properties of the CVD diodes are due to the formation of defects at the interface between the emitter and base layers.     

Double-diffused IMPATT diodes without substrate for X-band frequencies

The fabrication of double-diffused IMPATT diodes without substrate is described. The advantages of these diodes are shown in comparison to conventional Impatt diodes having an epitaxial nn⁺-transition. The double-diffused diodes deliver higher output power and efficiency. Saturation of the efficiency occurs at higher d.c.-current levels.     

Effects of internal fields on deep-level emission in InGaN/GaN quantum-well light-emitting diodes

We report on the important role played by internal quantum well (QW) fields in the anomalous inversion of capacitance transients in InGaN/GaN multi-QW light-emitting diodes (LEDs). This effect was observed by deep-level transient spectroscopy (DLTS) characterization. Deep-level C (E_C-E_T=0.25 eV), a majority carrier trap related to isolated point defects, gives rise to a negative transient when the bias stimulates it only in the bulk region and to a positive transient when the filling pulse is such that the QW region is probed. We explain this behavior by a model based on the confining effects of QW internal fields on the charge emitted by deep levels.     

Electron bombardment effect on the reverse I–V characteristics and tensosensibility of p+-nGaAs diodes

The effect of ≈2 MeV electron bombardment on the reverse characteristics and tensoelectric properties in p⁺-nGaAs diodes is investigated. The reverse breakdown voltage showed a weak increase due to irradiation and an anomalous temperature dependence in the range 77–300 K. The I–V characteristics in electron-irradiated diodes revealed a high pressure sensitivity (tensosensibility) to the external hydrostatic pressure (up to 6 · 10⁸ Pa). The peculiarities in the reverse I–V characteristics of diodes investigated point to the presence of a radiation-induced deep trap (acceptor-type level at about E₀ ? 0.3 + 0.4 eV), which is attached to the Γ₁₅^V-maximum of the valence band.     

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.     

Improved degradation stability of blue-green II-VI light-emitting diodes with excluded nitrogen-doped ZnSe-based layers

Degradation characteristics of p-i-n BeZnSe/Zn(Be)CdSe light-emitting diodes were investigated. Undoped short-period superlattices, which provide efficient hole transport from the p ⁺-BeTe:N near-contact region (hole injector) into the active region, were used instead of the p-doped BeZnSe:N emitter. It is demonstrated that this makes it possible to considerably lengthen the operating life of the light-emitting diodes at highest direct current densities (～4.5 kA/cm²) at room temperature.     

Grain boundary states and the characteristics of lateral polysilicon diodes

In lateral n⁺p^?p⁺ diodes made in LPCVD polycrystalline silicon films, the energy distribution of the traps at the grain boundaries is found to be U shaped. They have a density of about 10¹² cm^?2 and a capture cross section of about 10^?16 cm². The forward current of the diodes is ascribed to recombination, the reverse current to field-enhanced generation via these traps.     

Interaction of hydrogen with radiation defects in p-Si crystals

Interaction of hydrogen with radiation defects in p-Si crystals was studied by deep-level transient spectroscopy. Hydrogen was introduced into the electron-irradiated crystals using wet chemical etching in a solution of nitric and hydrofluoric acids at room temperature with subsequent annealing at 380 K under reverse bias applied to the formed Schottky diodes. It is found that the passivation of radiation defects is accompanied with the formation of new electrically active centers with the concentration profile dependent on the hydrogen concentration. It is shown for the first time that hydrogen passivates the electrical activity of the C_sC_i centers. Based on the data about the spatial distribution of defects and the kinetics of passivation, the plausible origin of the newly formed centers is analyzed. The radii of hydrogen capture by divacancies, the K centers, the C_sC_i complexes, and new centers were determined.     

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.