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.     

Low-temperature (77 K) impurity breakdown in <Emphasis Type="Italic">p</Emphasis>-type 4<Emphasis Type="Italic">H</Emphasis>-SiC

The impact ionization of acceptors in aluminum-doped 4H-SiC epitaxial films (Al concentration 2 × 10¹⁵ cm^?3) at a temperature of 77 K is studied. It is found that the impact-ionization coefficient exponentially depends on the reverse electric field: α _p = α*_pexp(?F*/F). The largest ionization coefficient is α* _p = 7.1 × 10⁶ cm^?3 s^?1, and the threshold field is F* = 2.9 × 10⁴ V/cm.     

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.     

Study of the 3<Emphasis Type="Italic">C</Emphasis>-SiC layers grown on the 15<Emphasis Type="Italic">R</Emphasis>-SiC substrates

The 3C-SiC layers grown on the 15R-SiC substrates by sublimation epitaxy in vacuum are studied. Using X-ray topography and Raman spectroscopy, it is shown that the obtained layers are of a rather high structural quality. By the data of the Raman spectroscopy and capacitance-voltage measurements, it is established that the electron concentration in the 3C-SiC layer is (4–6) × 10¹⁸ cm^?3.     

Irradiation of 4<Emphasis Type="Italic">H</Emphasis>-SiC UV detectors with heavy ions

Ultraviolet (UV) photodetectors based on Schottky barriers to 4H-SiC are formed on lightly doped n-type epitaxial layers grown by the chemical vapor deposition method on commercial substrates. The diode structures are irradiated at 25°C by 167-MeV Xe ions with a mass of 131 amu at a fluence of 6 × 10⁹ cm^?2. Comparative studies of the optical and electrical properties of as-grown and irradiated structures with Schottky barriers are carried out in the temperature range 23–180°C. The specific features of changes in the photosensitivity and electrical characteristics of the detector structures are accounted for by the capture of photogenerated carriers into traps formed due to fluctuations of the conduction-band bottom and valence-band top, with subsequent thermal dissociation.     

Special features of formation and characteristics of Ni/21<Emphasis Type="Italic">R</Emphasis>-SiC Schottky diodes

The Ni/n-21R-SiC(0001) and \(Ni/n - 21R - SiC(000\bar 1)\) surface-barrier structures formed on 21R-SiC crystals doped to a concentration of (1–2)×10¹⁸ cm^?3 and grown by the Lely method were investigated prior to and after rapid thermal annealing (RTA) in vacuum (10^?2 Pa) in the temperature range of 450–1100°C. Using X-ray diffraction analysis and Auger analysis, it is shown that cubic NiSi₂ and orthorhombic δ-Ni₂Si and NiSi silicides coexist with pure Ni in starting samples. The RTA brings about a polymorphic transformation of these phases, which causes the transformation of a barrier contact to a rectifying one independently of the SiC face type, even at T?600°C. The physicochemical mechanisms of degradation of these barrier structures are discussed.     

Au-TiB<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-<Emphasis Type="Italic">n</Emphasis>-6<Emphasis Type="Italic">H</Emphasis>-SiC Schottky barrier diodes: Specific features of charge transport in rectifying and nonrectifying contacts

Mechanism of charge transport in a diode of a silicon carbide’s Schottky barrier formed by a quasi-amorphous interstitial phase TiB _x on the surface of n-6H-SiC (0001) single crystals with an uncompensated donor (nitrogen) concentration of ～10¹⁸ cm^?3 and dislocation density of ～(10⁶–10⁸) cm^?2 has been studied. It is demonstrated that, at temperatures T ? 400 K, the charge transport is governed by the tunneling current along dislocations intersecting the space charge region. At T > 400 K, the mechanism of charge transport changes to a thermionic mechanism with a barrier height of ～0.64 eV and ideality factor close to 1.3.     

Fine Structure of the long-wavelength edge of exciton-phonon absorption and hyperbolic excitons in silicon carbide of 6<Emphasis Type="Italic">H</Emphasis> polytype

The fine structure of the long-wavelength edge of the polarization spectra of exciton-phonon absorption in moderate-purity n-type 6H-SiC crystals with a concentration of uncompensated donors N_D?N_A=(1.7–2.0)×10¹⁶ cm^?3 at T=1.7 K was studied. The analysis of new special features found at the absorption edge and the reliable detection of the onset of exciton-phonon steps related to the emission of phonons from acoustical and optical branches allowed highly accurate determination of a number of important parameters such as the band gap, the exciton band gap, the exciton binding energy, and the energies of spin-orbit and crystal-field splitting of an exciton. For the first time, transitions with the emission of LA phonons to the 1S exciton state with an M₁-type dispersion law were detected in E ∥ Z(C) polarization (the electric-field vector is parallel to the optical axis of the crystal). This observation supports the previously predicted “two-well” structure of the conduction band minimum in 6H-SiC.     

Electrical properties of Si:H/<Emphasis Type="Italic">p</Emphasis>-Si structures fabricated by hydrogen implantation

Hydrogenated silicon (Si:H) layers and Si:H/p-Si heterostructures were produced by multiple-energy (3–24 keV) high-dose (5×10¹⁶–3×10¹⁷ cm^?2) hydrogen implantation into p-Si wafers. After implantation, current transport across the structures is controlled by the Poole-Frenkel mechanism, with the energy of the dominating emission center equal to E _c ?0.89 eV. The maximum photosensitivity is observed for structures implanted with 3.2×10¹⁷ cm^?2 of hydrogen and annealed in the temperature range of 250–300°C. The band gap of the Si:H layer E _g ≈2.4 eV, and the dielectric constant ?≈3.2. The density of states near the Fermi level is (1–2)×10¹⁷ cm^?3 eV^?1.     

Specific features of electron spin resonance in 4<Emphasis Type="Italic">H</Emphasis>-SiC in the vicinity of the insulator-metal phase transition: II. Analysis of the width and shape of lines

The variation in the width and shape of the ESR line of nitrogen in 4H-SiC in the concentration range corresponding to the insulator-metal phase transition was investigated. It is shown that the spin relaxation in the region of hopping and metal conduction occurs at electrical multipoles (clusters) whose sizes decrease from rather large to small (characteristic of interimpurity distances) as the concentration of impurity centers increases. Analysis of the temperature dependences of the resistance made it possible to estimate the critical concentration for the insulator-metal phase transition (N _D -N _A )_c≈1.5×10¹⁹ cm^?3. The values of other characteristic concentrations that determine the effects of electron-electron interaction in the system under study were also found.     

3<Emphasis Type="Italic">C</Emphasis>-SiC <Emphasis Type="Italic">p-n</Emphasis> structures grown by sublimation on 6<Emphasis Type="Italic">H</Emphasis>-SiC substrates

Sublimation epitaxy in a vacuum has been employed to grow n-and p-type 3C-SiC layers on 6H-SiC substrates. Diodes have been fabricated on the basis of the p-n structure obtained, and their parameters have been studied by measuring their current-voltage and capacitance-voltage characteristics and by applying the DLTS and electroluminescence methods. It is shown that the characteristics of the diodes studied are close to those of diodes based on bulk 3C-SiC. A conclusion is made that sublimation epitaxy can be used to fabricate 3C-SiC p-n structures on substrates of other silicon carbide polytypes.     

Features of the band structure and conduction mechanisms of <Emphasis Type="Italic">n</Emphasis>-HfNiSn heavily doped with Y

The crystalline and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with Y acceptor impurity are studied in the ranges: T = 80–400 K, N _A ^Y ≈ 1.9 × 10²⁰–5.7 × 10²¹ cm^–3 (x = 0.01–0.30), and H ≤ 10 kG. The nature of the mechanism of structural defect generation is determined, which leads to a change in the band gap and the degree of semiconductor compensation, the essence of which is the simultaneous reduction and elimination of structural donor-type defects as a result of the displacement of ~1% of Ni atoms from the Hf (4a) site, and the generation of structural acceptor-type defects by substituting Hf atoms with Y atoms at the 4a site. The results of calculations of the electronic structure of Hf_1–x Y _x NiSn are in agreement with the experimental data. The discussion is performed within the Shklovskii–Efros model of a heavily doped and compensated semiconductor.     

Effect of irradiation with fast neutrons on electrical characteristics of devices based on CVD 4<Emphasis Type="Italic">H</Emphasis>-SiC epitaxial layers

The effect of irradiation with 1-MeV neutrons on electrical properties of Al-based Schottky barriers and p⁺-n-n⁺ diodes doped by ion-implantation with Al was studied; the devices were formed on the basis of high-resistivity, pure 4H-SiC epitaxial layers possessing n-type conductivity and grown by vapor-transport epitaxy. The use of such structures made it possible to study the radiation defects in the epitaxial layer at temperatures as high as 700 K. Rectifying properties of the diode structures were no longer observed after irradiation of the samples with neutrons with a dose of 6×10¹⁴ cm^?2; this effect is caused by high (up to 50 GΩ) resistance of the layer damaged by neutron radiation. However, the diode characteristics of irradiated p⁺-n-n⁺ structures were partially recovered after an annealing at 650 K.     

Characterization of <Emphasis Type="Italic">n</Emphasis>-Type and <Emphasis Type="Italic">p</Emphasis>-Type Long-Wave InAs/InAsSb Superlattices

The influence of dopant concentration on both in-plane mobility and minority carrier lifetime in long-wave infrared InAs/InAsSb superlattices (SLs) was investigated. Unintentially doped (n-type) and various concentrations of Be-doped (p-type) SLs were characterized using variable-field Hall and photoconductive decay techniques. Minority carrier lifetimes in p-type InAs/InAsSb SLs are observed to decrease with increasing carrier concentration, with the longest lifetime at 77 K determined to be 437 ns, corresponding to a measured carrier concentration of p ₀ = 4.1 × 10¹⁵ cm^?3. Variable-field Hall technique enabled the extraction of in-plane hole, electron, and surface electron transport properties as a function of temperature. In-plane hole mobility is not observed to change with doping level and increases with reducing temperature, reaching a maximum at the lowest temperature measured of 30 K. An activation energy of the Be-dopant is determined to be 3.5 meV from Arrhenius analysis of hole concentration. Minority carrier electrons populations are suppressed at the highest Be-doping levels, but mobility and concentration values are resolved in lower-doped samples. An average surface electron conductivity of 3.54 × 10^?4 S at 30 K is determined from the analysis of p-type samples. Effects of passivation treatments on surface conductivity will be presented.     

Study of the impurity photoconductivity in <Emphasis Type="Italic">p</Emphasis>-InSb using epitaxial <Emphasis Type="Italic">p</Emphasis> <Superscript>+</Superscript> contacts

The optical absorption coefficient α in p⁺-InSb layers (with hole concentrations of p ≈ 1 × 10¹⁷–1.2 × 10¹⁹ cm^–3), grown by liquid-phase epitaxy on p-InSb substrates, is measured in the spectral range of 5-12 µm at 90 K, and the impurity photoconductivity is measured (at 60 and 90 K) in p⁺–p structures. It is found that a in the p⁺ layers reaches a value of 7000 cm^–1 (at p ≈ 2 × 10¹⁹ cm^–1). It is shown that the measured substrate value of (α ≈1–3 cm^–1) is overestimated in comparison with estimates (α ≈ 0.1 cm^–1) based on comparing the photoconductivity data. This discrepancy is explained by the fact that the optical transitions of holes responsible for photoconductivity are obscured by the excitation of electrons to the conduction band. The photoionization cross section for these transitions does not exceed 1 × 10^–15 cm².     

Features of structural,electron-transport,and magnetic properties of heavily doped <Emphasis Type="Italic">n</Emphasis>-ZrNiSn semiconductor: Fe acceptor impurity

Structural, energy, electron-transport, and magnetic characteristics of the n-ZrNiSn intermetallic semiconductor heavily doped with Fe (the concentration N _Fe ≈ 9.7 × 10¹⁹?3.8 × 10²¹ cm^?3) in the temperature range T = 80–380 K are investigated. It is shown that the Fe atoms simultaneously occupy crystallographic sites of Zr and Ni atoms in different relations being the defects of the donor and acceptor nature, respectively. The relation between the impurity concentration, the amplitude of large-scale fluctuation, and the degree of filling of the potential well of the small-scale fluctuation (fine structure) by charge carriers is established. The results are discussed within the context of the Shklovskii-Efros model of a heavily doped and compensated semiconductor.     

Field dependence of the electron drift velocity along the hexagonal axis of 4<Emphasis Type="Italic">H</Emphasis>-SiC

The forward current–voltage characteristics of mesa-epitaxial 4H-SiC Schottky diodes are measured in high electric fields (up to 4 × 10⁵ V/cm) in the n-type base region. A semi-empirical formula for the field dependence of the electron drift velocity in 4H-SiC along the hexagonal axis of the crystal is derived. It is shown that the saturated drift velocity is (1.55 ± 0.05) × 10⁷ cm/s in electric fields higher than 2 × 10⁵ V/cm.     

Interaction of charge carriers with the localized magnetic moments of manganese atoms in <Emphasis Type="Italic">p</Emphasis>-GaInAsSb/<Emphasis Type="Italic">p</Emphasis>-InAs:Mn heterostructures

Transport properties of p-Ga_1?xIn_xAs_ySb_1?y/p-InAs:Mn heterostructures with undoped layers of solid solutions similar in composition to GaSb (x?0.22) grown by liquid-phase epitaxy on substrates with a Mn concentration of (5–7)×10¹⁸ cm^?3 are studied. It is ascertained that there is an electron channel at the interface (from the InAs side). The anomalous Hall effect and negative magnetoresistance are observed at relatively high temperatures (77–200) K. These phenomena can be attributed to the s-d-exchange interaction between Mn ions of the substrate and s electrons of the two-dimensional channel. The effective magnetic moment of Mn ions was evaluated as μ=200µ_B at T=77 K.     

Surface states on the <Emphasis Type="Italic">n</Emphasis>-InN-electrolyte interface

Dependences of differential capacitance of the electrolyte-n-InN (0001) contact on the bias voltage are studied. Their analysis of the basis of a model similar to a model of the MIS structure shows that the energy spectrum of surface states of InN above the conduction band bottom can be represented by two, relatively narrow, bands of deep levels described by the Gaussian distribution. Parameters of these bands are as follows: the average energy counted from the conduction band bottom, ΔE ₁ ≈ 0.15 eV and ΔE ₂ ≈ 0.9 eV; and the mean-square deviation, ΔE ₁ ≈ 0.15–0.25 eV and ΔE ₂ ≈ 0.05–0.1 eV. The total density of states in the bands are (1–2.5) × 10¹² and (0.2–4) × 10¹² cm^–2.