A 4<Emphasis Type="Italic">H</Emphasis>-SiC<Emphasis Type="Italic">p-i-n</Emphasis> diode fabricated by a combination of sublimation epitaxy and CVD

The possibility of fabricating heavily doped (N _a ?N _d ≥ 1 × 10¹⁹ cm_?3) p⁺-4H-SiC layers on CVD-grown lightly doped n-4H-SiC layers by sublimation epitaxy has been demonstrated. It is shown that a Au/Pd/Ti/Pd contact, which combines a low specific contact resistance (～2 × 10^?5 Ω cm²) with high thermal stability (up to 700°C), is the optimal contact to p-4H-SiC. The p-n structures obtained are used to fabricate packaged diodes with a breakdown voltage of up to 1400 V.     

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.     

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.     

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.     

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.     

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.     

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.     

Structural and Electrical Properties of Ag/<Emphasis Type="Italic">n</Emphasis>-TiO<Subscript>2</Subscript>/<Emphasis Type="Italic">p</Emphasis>-Si/Al Heterostructure Fabricated by Pulsed Laser Deposition Technique

We have investigated the structural and electrical characteristics of the Ag/n-TiO₂/p-Si/Al heterostructure. Thin films of pure TiO₂ were deposited on p-type silicon (100) by optimized pulsed laser ablation with a KrF-excimer laser in an oxygen-controlled environment. X-ray diffraction analysis showed the formation of crystalline TiO₂ film having a tetragonal texture with a strong (210) plane as the preferred direction. High purity aluminium and silver metals were deposited to obtain ohmic contacts on p-Si and n-TiO₂, respectively. The current–voltage (I–V) characteristics of the fabricated heterostructure were studied by using thermionic emission diffusion mechanism over the temperature range of 80–300 K. Parameters such as barrier height and ideality factor were derived from the measured I–V data of the heterostructure. The detailed analysis of I–V measurements revealed good rectifying behavior in the inhomogeneous Ag/n-TiO₂/p-Si(100)/Al heterostructure. The variations of barrier height and ideality factor with temperature and the non-linearity of the activation energy plot confirmed that barrier heights at the interface follow Gaussian distributions. The value of Richardson’s constant was found to be 6.73 × 10⁵ Am^?2 K^?2, which is of the order of the theoretical value 3.2 × 10⁵ Am^?2 K^?2. The capacitance–voltage (C–V) measurements of the heterostructure were investigated as a function of temperature. The frequency dependence (Mott–Schottky plot) of the C–V characteristics was also studied. These measurements indicate the occurrence of a built-in barrier and impurity concentration in TiO₂ film. The optical studies were also performed using a UV–Vis spectrophotometer. The optical band gap energy of TiO₂ films was found to be 3.60 eV.     

Special features of annealing of radiation defects in irradiated <Emphasis Type="Italic">p</Emphasis>-Si crystals

p-Si single crystals grown by the Czochralski method were studied; the hole concentration in these crystals was p = 6 × 10¹³ cm^?3. The samples were irradiated with 8-MeV electrons at 300 K and were then annealed isochronously in the temperature range T _ann = 100–500°C. The studies were carried out using the Hall method in the temperature range of 77–300 K. It is shown that annealing of divacancies occurs via their transformation into the B _s V ₂ complexes. This complex introduces the energy level located at E _v + 0.22 eV into the band gap and is annealed out in the temperature range of 360–440°C. It is assumed that defects with the level E _v + 0.2 eV that anneal out in the temperature range T _ann = 340–450°C are multicomponent complexes and contain the atoms of the doping and background impurities.     

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.     

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.     

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 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.     

Giant burst of impact ionization in a <Emphasis Type="Italic">p-n</Emphasis> junction of the 6<Emphasis Type="Italic">H</Emphasis>-SiC polytype

A study of the electron component of impact ionization in the p ⁺-n ^?-n ⁺ junction in the 6HSiC polytype made it possible to detect a giant burst of impact ionization and origination of an extra early avalanche breakdown. The electric field of this breakdown is lower by ～20% than the electric field of the breakdown arising as a result of a steady development of the impact ionization. It is of interest that this phenomenon occurs abruptly, without any apparent causes, in particular, without an increase in the dark current characteristic of a prebreakdown state of the p-n junction. Conditions for origination of an unusual breakdown and its properties made it possible to assume that there are nonlinear processes that give rise to a streamer. In the p-n junction plane, the anomalous breakdown is seen as a narrow glowing track with a width of ≈10 μm. This effect takes place in the conditions of the Wannier-Stark ladder of states. The latter can stimulate a local accumulation of charge and formation of a streamer structure.     

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.     

<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.     

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.     

Carrier Lifetimes in Lightly-Doped <Emphasis Type="Italic">p</Emphasis>-Type 4H-SiC Epitaxial Layers Enhanced by Post-growth Processes and Surface Passivation

We investigated limiting factors of carrier lifetimes and their enhancement by post-growth processes in lightly-doped p-type 4H-SiC epitaxial layers (N _A ～ 2 × 10¹⁴ cm^?3). We focused on bulk recombination, surface recombination, and interface recombination at the epilayer/substrate, respectively. The carrier lifetime of 2.8 μs in an as-grown epilayer was improved to 10 μs by the combination of V_C-elimination processes and hydrogen annealing. By employing surface passivation with deposited SiO₂ followed by POCl₃ annealing, a long carrier lifetime of 16 μs was obtained in an oxidized epilayer. By investigating carrier lifetimes in a self-standing p-type epilayer, it was revealed that the interface recombination at the epilayer/substrate was smaller than the surface recombination on a bare surface. We found that the V_C-elimination process, hydrogen annealing, and surface passivation are all important for improving carrier lifetimes in lightly-doped p-type epilayers.     

Electrical and photoelectric properties of <Emphasis Type="Italic">n</Emphasis>-TiN/<Emphasis Type="Italic">p</Emphasis>-Hg<Subscript>3</Subscript>In<Subscript>2</Subscript>Te<Subscript>6</Subscript> heterostructures

n-TiN/p-Hg₃In₂Te₆ heterostructures are fabricated by depositing a thin n-type titanium nitride (TiN) film onto prepared p-type Hg₃In₂Te₆ plates using reactive magnetron sputtering. Their electrical and photoelectric properties are studied. Dominant charge-transport mechanisms under forward bias are analyzed within tunneling-recombination and tunneling models. The fabricated n-TiN/p-Hg₃In₂Te₆ structures have the following photoelectric parameters at an illumination intensity of 80 mW/cm²: the open-circuit voltage is V_OC = 0.52 V, the short-circuit current is I_SC = 0.265 mA/cm², and the fill factor is FF = 0.39.     

Electrical properties of Zinc-Tin diarsenide (ZnSnAs<Subscript>2</Subscript>) irradiated with H<Superscript>+</Superscript> ions

The results of studying the electrical properties and isochronous annealing of p-ZnSnAs₂ irradiated with H⁺ ions (energy E = 5 MeV, dose D = 2 × 10¹⁶ cm^?2) are reported. The limiting electrical characteristics of irradiated material (the Hall coefficient R _H (D)_lim ≈ ?4 × 10³ cm³ C^?1, conductivity σ (D)_lim ≈ 2.9 × 10^?2 Ω^?1 cm^?1, and the Fermi level position F _lim ≈ 0.58 eV above the valence-band top at 300 K) are determined. The energy position of the “neutral” point for the ZnSnAs₂ compound is calculated.