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.     

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.     

Radiation resistance of transistor-and diode-type SiC detectors irradiated with 8-MeV protons

Nuclear-particle detectors based on SiC with a structure composed of an n⁺-type substrate, a p-type epitaxial layer, and a Schottky barrier are studied. Structures with a ～10-µm-thick 6H-SiC layer exhibit transistor properties, whereas those with a ～30-µm-thick 4H-SiC layer exhibit diode properties. It is established that a more than tenfold amplification of the signal is observed in the transistor-type structure. The amplification is retained after irradiation with 8-MeV protons with a dose of at least 5×10¹³ cm^?2; in this case, the resolution is ≤10%. Amplification of the signal was not observed in the structures of diode type. However, there were diode-type detectors with a resolution of ≈3%, which is acceptable for a number of applications, even after irradiation with the highest dose of 2×10¹⁴ cm^?2.     

The effect of neutron irradiation on the properties of <Emphasis Type="Italic">n</Emphasis>-InSb whisker microcrystals

The results of studying the effect of irradiation with fast neutrons in an IBR-2 reactor on the characteristics of magnetic-field sensors based on n⁺-InSb whisker microcrystals are reported (the measurements were carried out in the course of the irradiation). The optimum concentration of free electrons n for providing the highest possible radiation resistance of the InSb sensors is estimated (n ≈ (6–7) × 10¹⁷ cm^?3). The contributions of two competing processes to variation in the electrical properties of InSb under neutron irradiation (transmutation-related doping of InSb with a Sn shallow-level donor impurity and compensation of the initial n⁺-InSb conductivity as a result of generation of deep-level acceptor-type radiation defects) are determined separately.     

<Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-Si-<Emphasis Type="Italic">n</Emphasis>-CdF<Subscript>2</Subscript> heterojunctions

Boron diffusion and the vapor-phase deposition of silicon layers are used to prepare ultrashallow p⁺-n junctions and p⁺-Si-n-CdF₂ heterostructures on an n-CdF₂ crystal surface. Forward portions of the I–V characteristics of the p⁺-n junctions and p⁺-Si-n-CdF₂ heterojunctions reveal the CdF₂ band gap (7.8 eV), as well as allow the identification of the valence-band structure of cadmium fluoride crystals. Under conditions in which forward bias is applied to the p⁺-Si-n-CdF₂ heterojunctions, electroluminescence spectra are measured for the first time in the visible spectral region.     

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.     

High-temperature nuclear-detector arrays based on 4 <Emphasis Type="Italic">H</Emphasis>-SiC ion-implantation-doped <Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-<Emphasis Type="Italic">n</Emphasis> junctions

Results obtained in a study of spectrometric characteristics of arrays of four detectors based on 4H-SiC ion-implantation-doped p ⁺-n junctions in the temperature range 25–140 °C are reported for the first time. The junctions were fabricated by ion implantation of aluminum into epitaxial 4H-SiC layers of thickness ≤45 μm, grown by chemical vapor deposition with uncompensated donor concentration N _d ? N _a = (4–6) × 10¹⁴ cm^?3. The structural features of the ion-implantation-doped p ⁺-layers were studied by secondary-ion mass spectrometry, transmission electron microscopy, and Rutherford backscattering spectroscopy in the channeling mode. Parameters of the diode arrays were determined by testing in air with natural-decay alpha particles with an energy of 3.76 MeV. The previously obtained data for similar single detectors were experimentally confirmed: the basic characteristics of the detector arrays, the charge collection efficiency and energy resolution, are improved as the working temperature increases.     

A method for measuring the lifetime of charge carriers in the base regions of high-speed diode structures

A method for measuring the lifetime of charge carriers in the base regions of p⁺-n-n⁺ structures is suggested. This method makes it possible to perform measurements in the nanosecond range of lifetimes. The developed technique implies the same shape of measuring current pulse as is used for conventional measurements of the restoring times in diode structures. The method is validated on the basis of an analysis of a solution to the continuity equation for holes in a base region. The results of the calculations are compared with experimental data.     

Self-Action of Intense Millimeter Waves in Waveguides with Integrated P-I-N Structures

The nonlinear interaction of high power millimeter (mm) electromagnetic waves with silicon integral p-i-n structures placed in a metal waveguide is theoretically investigated. The level of double injection of charge carriers due to detection of high intensity millimeter wave electric field in p-i-n structures is estimated. A mathematical model of the mutual influence of electromagnetic waves and injected charge carriers in the active region of p-i-n structures is formulated. A numerical solution of the nonlinear Helmholtz equation supplemented by proper boundary conditions on the active region boundary is obtained. The effect of high-power electromagnetic waves leads to an excessive injection of carriers into the active region of the semiconductor between p⁺-i, n⁺-i injection junctions and redistribution of the electric field in the structure. The reflection and transmission coefficients vary rapidly with the change in the input amplitude of the electromagnetic wave. This leads to bistability of these coefficients. The bistability is more pronounced in the low-frequency part of the mm range.     

Investigation of the ZnS-CdHgTe interface

The ZnS-Cd_xHg_1?xTe interface was investigated using the capacitance-voltage characteristics of MIS structures in experimental samples. During fabrication of the n⁺-p junctions based on p-Cd_xHg_1?xTe, the density of states within the range N _ss =(1–6)×10¹¹ cm^?2 eV^?1 at T=78 K was obtained. The experiments showed that the conditions in which n⁺-p junctions are fabricated only slightly affect the state of the ZnS-CdHgTe interface. The negative voltages of the at bands V _FB , even if immediately after deposition of the ZnS films V _FB >0, point to the enrichment of the ZnS-p-CdHgTe near-surface layer with majority carriers, specifically, holes. This led to a decrease in the leakage current over the surface. During long-term storage (as long as ～15 years) in air at room temperature, no degradation of differential resistance R _d , current sensitivity S _i , and detectivity D* of such n⁺-p junctions with a ZnS protection film was observed.     

Control over carrier lifetime in high-voltage <Emphasis Type="Italic">p-i-n</Emphasis> diodes based on In<Subscript>x</Subscript>Ga<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>As/GaAs heterostructures

The possibility of controlling the effective lifetime of nonequilibrium carriers by varying the lattice mismatch between the interfaced materials of a heterostructure has been studied on the example of InGaAs/GaAs heterostructures. It was found that, at a given composition (thickness) of a lightly doped layer of the InGaAs alloy, the nonequilibrium carrier lifetime depends on its thickness (composition), which enables variation of the nonequilibrium carrier lifetime from several nanoseconds to a microsecond without any significant change in the concentration of mobile carriers. The results obtained were used to fabricate pulse p ⁺-p ⁰-π-n ⁰-n ⁺ diodes with blocking voltages of up to 500 V, which can switch currents of ≥10 A and have recovery times no longer than 10 ns.     

Diamond Diode Structures Based on Homoepitaxial Films

(m–i–p)-Structures with high-resistance epitaxial i-layers are fabricated on heavily doped p⁺-type substrates with platinum contacts. The structures are studied using several methods: optical and electron microscopy and luminescence, and electrophysical (C–V and I–V characteristics) methods and tested as detectors of ionizing radiation. It is shown that the (m–i–p)-structures are promising for development of several electronic devices (high-voltage diodes, detectors of ionizing radiation, and photovoltaic devices).     

Electrical properties of <Emphasis Type="Italic">n-</Emphasis>GaN/<Emphasis Type="Italic">p</Emphasis>-SiC heterojunctions

Epitaxial GaN layers were grown by hydride vapor phase epitaxy (HVPE) on commercial (CREE Inc., USA) p⁺-6H-SiC substrates (Na ? Nd ≈ 7.8 × 10¹⁷ cm^s?3) and n⁺-6H-SiC Lely substrates with a predeposited p⁺-6H-SiC layer. A study of the electrical properties of the n-GaN/p-SiC heterostructures obtained confirmed their fairly good quality and demonstrated that the given combination of growth techniques is promising for fabrication of bipolar and FET transistors based on the n-GaN/p-SiC heterojunctions.     

High-voltage (900 V) 4 <Emphasis Type="Italic">H</Emphasis>-SiC Schottky diodes with a boron-implanted guard <Emphasis Type="Italic">p-n</Emphasis> junction

High-voltage (900 V) 4H-SiC Schottky diodes terminated with a guard p-n junction were fabricated and studied. The guard p-n junction was formed by room-temperature boron implantation with subsequent high-temperature annealing. Due to transient enhanced boron diffusion during annealing, the depth of the guard p-n junction was equal to about 1.7 μm, which is larger by approximately 1 μm than the projected range of 11 B ions in 4H-SiC. The maximum reverse voltage of fabricated 4H-SiC Schottky diodes is found to be limited by avalanche breakdown of the planar p-n junction; the value of the breakdown voltage (910 V) is close to theoretical estimate in the case of the impurity concentration N = 2.5 × 10¹⁵ cm^?3 in the n-type layer, thickness of the n-type layer d = 12.5 μm, and depth of the p-n junction r _j = 1.7 μm. The on-state diode resistance (3.7 mΩ cm²) is controlled by the resistance of the epitaxial n-type layer. The recovery charge of about 1.3 nC is equal to the charge of majority charge carriers that are swept out of an epitaxial n-type layer under the effect of a reverse voltage.     

Measurements of electrophysical characteristics of semiconductor structures with the use of microwave photonic crystals

A method is proposed for the measurement of the electrophysical characteristics of semiconductor structures: the electrical conductivity of the n layer, which plays the role of substrate for a semiconductor structure, and the thickness and electrical conductivity of the strongly doped epitaxial n ⁺ layer. The method is based on the use of a one-dimensional microwave photonic crystal with a violation of periodicity containing the semiconductor structure under investigation. The characteristics of epitaxial gallium-arsenide structures consisting of an epitaxial layer and the semi-insulating substrate measured by this method are presented.     

Anomalous dependences of the diode barrier capacitance on bias voltage and temperature

Capacitances of a Schottky barrier and p ⁺-n junction whose n-type regions contain shallow donors and deep acceptors with levels in the upper part of the energy gap have been calculated. The capacitance was represented as two series capacitances of the near-contact region containing only donor impurity ions and of the intermediate layer at the interface between the space-charge region and the diode base, with account of the free-carrier concentration and its dependence on the potential. It was found that the capacitance of the intermediate layer heavily depends on temperature and may increase with the bias voltage. The calculated capacitancevoltage characteristics of the barrier capacitance are in agreement with experimental data and even describe the nonmonotonic dependences of the capacitance on the bias voltage.     

Special features of radiation-defect annealing in silicon <Emphasis Type="Italic">p-n</Emphasis> structures: The role of Fe impurity atoms

Deep-level transient spectroscopy is used to study the formation of complexes that consist of a radiation defect and a residual impurity atom in silicon. It is established that heat treatment of the diffused Si p⁺-n junctions irradiated with fast electrons lead to the activation of a residual Fe impurity and the formation of the FeVO (E_0.36 trap) and FeV₂ (H_0.18 trap) complexes. The formation of these traps is accompanied by the early (100–175°C) stage of annealing of the main vacancy-related radiation defects: the A centers (VO) and divacancies (V₂). The observed complexes are electrically active and introduce new electron (E_0.36: E _t ^e =E _c -0.365 eV, σ _n =6.8×10^?15 cm²) and hole (H_0.18: E _t ^h =E _v +0.184 eV, σ _p =3.0×10^?15 cm²) levels into the silicon band gap and have a high thermal stability. It is believed that the complex FeVO corresponds to the previously observed and unidentified defects that have an ionization energy of E _t ^e =E _c ?(0.34–0.37) eV and appear as a result of heat treatment of irradiated diffused Si p⁺-n junctions.     

Study of deep levels in GaAs <Emphasis Type="Italic">p–i–n</Emphasis> structures

An experimental study of the capacitance–voltage (C–V) characteristics and deep-level transient spectroscopy (DLTS) of p⁺–p⁰–i–n⁰ structures based on undoped GaAs, grown by liquid-phase epitaxy at two crystallization-onset temperatures T_o (950 and 850°C), with optical illumination switched off and on, are performed. It is shown that the p⁰, i, and n⁰ layers of epitaxial structures are characterized by the presence of defects with deep donor- and acceptor-type levels in concentrations comparable with those of shallow donors and acceptors. Interface states are found, which manifest themselves in the C–V characteristics at different measurement temperatures and optical illumination; these states form an additive constant. A distinct temperature dependence of the steady-state capacitance of the structures is revealed. It is found that the injection of minority carriers under an applied positive filling pulse and optical recharging lead to modification of the structure and, correspondingly, the DLTS spectra of the p⁺–p⁰–i–n⁰ structures. It is revealed that the p⁺–p⁰–i–n⁰ GaAs structures grown at T_o = 850°C are characterized by a lack of interface states and that the recharging of acceptor-type deep traps under illumination does not change the C–V characteristics. The conventionally measured DLTS spectra reveal the presence of two hole traps: HL5 and HL2, which are typical of GaAs layers.     

“Ideal” static breakdown in high-voltage (1 kV) 4<Emphasis Type="Italic">H</Emphasis>-SiC<Emphasis Type="Italic">p-n</Emphasis> junction diodes with guard ring termination

Nearly “ideal” static high-voltage breakdown (1060 V) in 4H-SiC p⁺-n-n⁺ diodes with guard ring termination is observed. At the doping level of 1.9 × 10¹⁶ cm^?3 in the n-type base, the diode breakdown field is 2.7 × 10⁶ V/cm. At the reverse bias as high as 1000 V, the leakage-current density does not exceed 5 × 10^?5 A/cm². The diodes withstand without degradation an avalanche-current density of 1 A/cm², which corresponds to the dissipated power of 1 kW/cm².