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.     

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.     

Electrical properties of the <Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>-<Emphasis Type="Italic">p</Emphasis>-GaSe isotype heterostructure

Electrical properties of a p⁺-Bi₂Te₃-p-GaSe isotype heterostructure fabricated for the first time are reported. A qualitative model is suggested which explains the emergence of negative differential conductivity for a forward-biased structure and for a reverse-biased structure, which is also illuminated.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

High-efficiency LEDs based on <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">p</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb/<Emphasis Type="Italic">P</Emphasis>-AlGaAsSb type-II thyristor heterostructures

A new type of light-emitting diodes (LEDs), a high-efficiency device based on an n-GaSb/p-GaSb/n-GaInAsSb/P-AlGaAsSb thyristor heterostructure, with the maximum emission intensity at wavelength λ = 1.95 μm, has been suggested and its electrical and luminescent characteristics have been studied. It is shown that the effective radiative recombination in the thyristor structure in the n-type GaInAsSb active region is provided by double-sided injection of holes from the neighboring p-type regions. The maximum internal quantum efficiency of 77% was achieved in the structure under study in the pulsed mode. The average optical power was as high as 2.5 mW, and the peak power in the pulsed mode was 71 mW, which exceeded by a factor of 2.9 the power obtained with a standard n-GaSb/n-GaInAsSb/P-AlGaAsSb LED operating in the same spectral range. The approach suggested will make it possible to improve LED parameters in the entire mid-IR spectral range (2–5 μm).     

Study of the intermediate layer at the <Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript>-CdS/<Emphasis Type="Italic">p</Emphasis>-CdTe interface

The effect of production conditions and subsequent stimulation by ultrasonic irradiation on the formation of a solid solution at the n-CdS/p-CdTe interface in solar cells has been investigated. The phase composition of the solid-solution transient layer was investigated by a nondestructive photoelectric method (measurement of the spectral distribution of photosensitivity in the gate and photodiode modes). It is shown that the phase composition and thickness of the intermediate CdTe_1?x S _x layer depend strongly on the heterostructure formation conditions.     

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.     

On the laser detachment of <Emphasis Type="Italic">n</Emphasis>-GaN films from substrates,based on the strong absorption of IR light by free charge carriers in <Emphasis Type="Italic">n</Emphasis> <Superscript>+</Superscript>-GaN substrates

The physical and technological basics of the method used to lift off lightly and moderately doped n-GaN films from heavily doped n⁺-GaN substrates are considered. The detachment method is based on the free-charge-carrier absorption of IR laser light, which is substantially higher in n⁺-GaN films.     

Electrical properties of <Emphasis Type="Italic">n</Emphasis>-ZnO/<Emphasis Type="Italic">p</Emphasis>-CuO heterostructures

The n-ZnO/p-CuO heterostructure is prepared, and its I-V characteristic is measured. It is shown that the heterostructure conductivity is primarily determined by the CuO layer and the n-ZnO/p-CuO heterojunction itself.     

Accumulation of structural defects in silicon irradiated with PF<Stack><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><Superscript>+</Superscript></Stack> cluster ions with medium energies

The method of Rutherford backscattering spectrometry in combination with channeling is used to study the accumulation of structural defects in silicon at room temperature as a result of irradiation with P⁺ and F⁺ atomic ions and also with cluster PF _n ⁺ ions (n = 1, …, 4) with the energy of 2.1 keV/amu and with identical generation rate of primary defects. The conditions for correct comparison of the results of bombardment with atomic and cluster ions composed of atoms of various types are suggested. It is found that the characteristics of accumulation of structural defects in silicon in the case of bombardment with PF _n ⁺ cluster ions differ widely from those under irradiation with both atomic ions that are involved in the cluster ion (P⁺ and F⁺) and with atomic heavy ions that have atomic mass close to that of the mass of a PF _n ⁺ cluster. It is shown that, with irradiation conditions being the same, cluster ions produce much more radiation defects in the surface region than do atomic ions; i.e., a molecular effect is observed. Plausible mechanisms of this phenomenon are considered.     

Optical storage on the basis of an <Emphasis Type="Italic">n</Emphasis>-InSb-SiO<Subscript>2</Subscript>-<Emphasis Type="Italic">p</Emphasis>-Si heterostructure

The presence of potential barriers and deep traps in n-InSb/SiO₂/p-Si heterostructures makes it possible to realize the optical memory function on the basis of this structure. The maximal memory coefficient measured on the forward current voltage characteristic is as large as ～10⁴. This heterostructure can be used as an optoelectronic memory cell, which provides a means not only for the storage of signals but also for their summation.