Electrical properties of isotype <Emphasis Type="Italic">N</Emphasis><Superscript>+</Superscript>-GaSb/n<Superscript>0</Superscript>-GaInAsSb/<Emphasis Type="Italic">N</Emphasis><Superscript>+</Superscript>-GaAlAsSb type-II heterojunctions

Band diagrams and current-voltage and capacitance-voltage characteristics of isotype N ⁺-GaSb/n⁰-GaInAsSb/N ⁺-GaAlAsSb heterostructures have been studied. Dark-current flow mechanisms have been analyzed. It is shown that a staggered type-II heterojunction can behave as a Schottky diode and its current-voltage characteristics exhibit rectifying properties over the entire temperature range 90–300 K. The thermionic-emission current predominates at high temperatures and low voltages. This current is due to thermal excitation of electrons from GaInAsSb to GaSb over the barrier at the heterointerface. A comparison of the relevant theoretical and experimental data confirmed that the tunneling charge transport mechanism plays the key role at low temperatures under both forward and reverse biases.     

Dependence of the binding energy of <Emphasis Type="Italic">A</Emphasis>(+) centers on quantum-well width in GaAs/AlGaAs structures

The luminescence of GaAs/AlGaAs multiple-quantum-well structures with different well widths, containing A(+) centers, was studied to determine the dependence of the center binding energy on quantum-well width. It is shown that the binding energy of the A(+) centers increases markedly with decreasing well width, becoming ten times greater in 10-nm-wide wells than in the bulk material. The binding energy of A(+) centers was found to depend on their concentration.     

Differential capacitance of a <Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-<Emphasis Type="Italic">p</Emphasis> junction

The differential capacitance of a p ⁺-p junction formed by charge redistribution near the junction, has been investigated taking into account the electric field in the quasi-neutral p region. The dependence of the capacitance and current of the p ⁺-p junction on its voltage is obtained. It is shown that a change in the sign of the p ⁺-p-junction capacitance with an increase in the injection level is caused by a decrease in the bipolar drift mobility in the p-type region. It is also demonstrated that a change in the sign of the p ⁺-p-junction capacitance with an increase in the reverse voltage determines the charge reduction near the junction, as the increase in the negative charge of acceptor ions predominates over the increase in the positive charge of holes.     

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 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.     

<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.     

Effect of potential fluctuations on the energy structure of GaAs/AlGaAs quantum wells with A<Superscript>+</Superscript> centers

The transformation of photoluminescence spectra associated with A⁺ centers in GaAs/AlGaAs quantum wells due to changes in the pumping level and temperature is analyzed. It is shown that an important part in the formation of the energy structure of the system of GaAs/AlGaAs quantum wells is played by electrostatic potential fluctuations responsible for the spatial redistribution of charge and the appearance of free holes.     

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.     

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).     

Light-Harvesting in <Emphasis Type="Italic">n</Emphasis>-ZnO/<Emphasis Type="Italic">p</Emphasis>-Silicon Heterojunctions

Zinc oxide (ZnO) films were deposited onto Si to form n-ZnO/p-Si heterojunctions. Under the illumination of by both ultraviolet (UV) light and sunlight, obvious photovoltaic behavior was observed. It was found that the conversion efficiency of the heterojunctions increased significantly with increasing thickness of the ZnO film, and the mechanism for light-harvesting in the heterojunctions is discussed. The results suggest that ZnO films may be helpful to increasing the harvesting of UV photons, thus decreasing the thermalization loss of UV energy in Si-based solar cells.     

Current instability with an <Emphasis Type="Italic">S</Emphasis>-shaped <Emphasis Type="Italic">I-V</Emphasis> characteristic in films of a metal-polymer complex of polyamide acid with Tb<Superscript>+2</Superscript>

The manifestation of current instability as an S-shaped I-V characteristic was detected in thin films of a metal-polymer complex of polyamide acid with Tb⁺². The current instability characteristics are comparable to those of the switching effect in chalcogenide glasses. The origin of the current instability in the metalpolymer complex may be related to electrothermal switching. The threshold voltage and current in films ～0.1 µm thick are 3–7 V and (2?1)×10^?2 A/cm², respectively.     

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.     

Thin-film polycrystalline <Emphasis Type="Italic">n</Emphasis>-ZnO/<Emphasis Type="Italic">p</Emphasis>-CuO heterojunction

Results of X-ray diffraction and spectral-optical studies of n-ZnO and p-CuO films deposited by gas-discharge sputtering with subsequent annealing are presented. It is shown that, despite the difference in the crystal systems, the polycrystallinity of n-ZnO and p-CuO films enables fabrication of a heterojunction from this pair of materials.     

On the maximum thickness of the space-charge region of reverse biased <Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-<Emphasis Type="Italic">n</Emphasis> junctions with a positive bevel

Two-dimensional potential and electric-field strength distributions in edge regions of sharply asymmetric reverse biased p ⁺-n junctions with a positive bevel were numerically simulated. It was shown that the maximum thickness of the space-charge region W _nM nonmonotonically depends on the angle θ between the bevel surface and junction plane: the function W _nM (θ) reaches a maximum at θ decreasing from 60° to 35° as the parameter Q _s /ɛ _s ɛ₀ EvM increases from 0 to 0.02 (here Q _s is the surface charge density, ɛ _s ɛ₀ is the absolute permittivity of the semiconductor, and E _vM is the maximum field strength in the space-charge region of the p ⁺-n junction far from the bevel). The results obtained may be useful in designing high-voltage thyristors based on Si, SiC, and other materials.     

Temperature dependence of the band structure of 3<Emphasis Type="Italic">C</Emphasis>, 2<Emphasis Type="Italic">H</Emphasis>, 4<Emphasis Type="Italic">H</Emphasis>, and 6<Emphasis Type="Italic">H</Emphasis> SiC polytypes

The temperature dependences of significant energy extrema at the high-symmetry points Γ, X, L, K, M, A, and H of the Brillouin zone in the cubic and hexagonal modifications of SiC, as well as the energies of the main interband transitions at these points, were calculated for the first time by the empirical-pseudopotential method. The effect of the temperature dependence of the electron-phonon interaction on the crystal band structure was taken into account via the Debye-Waller factors, and the contribution of the linear expansion of the lattice was accounted for via the temperature dependence of the linear-expansion coefficient. The special features of the temperature dependences of the energy levels and of energies of the interband and intraband transitions are analyzed in detail. The results of the calculations are in good agreement with the known experimental data on the characteristics of SiC-based p-n structures operating in the breakdown mode. For example, the temperature coefficient of the energy of the X_1c–X_3c transition, which is responsible for the narrow violet band in the breakdown-electroluminescence spectra of reverse-biased p-n junctions, was found to be significantly smaller than the temperature coefficients for the interband transitions (from the conduction to valence band). This fact is quite consistent with the experimental curve of the temperature coefficient of the emission spectrum, which has a minimum in the same wavelength range.     

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 <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.     

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.