Photoinduced relaxation of metastable states in (<Emphasis Type="Italic">a</Emphasis>-Si:H):B

The kinetics of thermal relaxation of an ensemble of photoinduced metastable electrically active B atoms in (a-Si:H):B films is studied after partial relaxation of the ensemble in the dark and under illumination of various intensities and duration. The parameters of a stretched exponential function that describes the ensemble kinetics are determined. It is found that photoinduced relaxation of metastable states manifests itself under conditions in which its rate exceeds the rate of the states’ photoinduced generation. It is shown that the variations in the relaxation-time distribution function of metastable states caused by thermal and photoinduced relaxation are similar.     

Light-induced relaxation of the metastable conductivity of undoped <Emphasis Type="Italic">a</Emphasis>-Si:H films illuminated at elevated temperatures

The kinetics of relaxation of the light-induced (at a temperature above 140°C) dark conductivity of undoped a-Si:H films is studied. The calculated time dependences of the relaxation rate of the dark conductivity are analyzed under the assumption that the thermal rates of the generation and relaxation of metastable defects formed by preliminary illumination are independent of illumination. It is shown that the features of the kinetics of the relaxation rates of dark conductivity under illumination are determined by the presence of light-induced processes of the relaxation and generation of slowly relaxing metastable defects whose energy levels are located in the upper half of the band gap.     

Effect of illumination on the rate of relaxation of light-induced metastable states in <Emphasis Type="Italic">a</Emphasis>-Si:H(B)

Time dependences of the rates of relaxation of light-induced metastable states of electrically active impurity atoms in boron-doped a-Si:H films have been studied in the dark and under illumination. It has been established that under illumination the rate of relaxation of light-induced metastable states of boron atoms grows in the initial stage when the rate of light-induced relaxation of these states exceeds that of their light-induced generation.     

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.     

1/<Emphasis Type="Italic">f</Emphasis> Noise in conducting Langmuir-Blodgett films of quasi-one-dimensional charge-transfer complexes

The noise characteristics of conducting Langmuir-Blodgett films of charge-transfer complexes (C₁₆H₃₃-TCNQ)_0.4(C₁₇H₃₅?DMTTF)_0.6 (surface-active complex based on a 1.5: 1.0 mixture of heptadecyldimethyltetrathiafulvalene (C₁₇H₃₅?DMTTF) and hexadecyltetracyanoquinodimethane (C₁₆H₃₃-TCNQ)) are studied. It is demonstrated that the excess (with respect to the thermal noise) electrical noise whose spectrum is close to 1/f dominates in the frequency range 1–10⁴ Hz. This noise has a bulk nature and arises owing to fluctuations of the film conductivity. The noise level is almost three orders of magnitude higher than the level predicted by the Hooge formula. A model that explains the film conductivity fluctuations by the superposition of relaxation processes of the on/off switching of conducting channels is proposed. In the framework of this model, a relationship that makes it possible to represent the level of the 1/f noise in terms of the parameters of a sample is derived. It is shown that the application of this relationship for the calculation of the 1/f noise magnitude in specific samples of conducting Langmuir-Blodgett films and TTF-TCNQ crystals yields results that are close to the experimental data.     

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.     

Effect of low-temperature annealing on electrical properties of <Emphasis Type="Italic">n</Emphasis>-HgCdTe

The effect of low-temperature isothermal annealing on electrical properties of Cd_xHg_1?xTe (mercury cadmium telluride, MCT) films is investigated. Films of n-type conduction with x=0.21–0.23 were grown on GaAs substrates by MBE. Annealings of 1–1000 h duration were carried out at 90–230°C. The changes in conductivity, the Hall factor, and the lifetime of minority carriers after annealing are explained by the formation of mercury vacancies and egress of Hg atoms from the sample. The effect of various surface coatings on the rate of variation of MCT film electrical properties was investigated. An anodic oxide appeared to be the most efficient coating to stabilize the parameters of n-type films. The analysis of the magnetic-field dependences of the Hall factor and conductivity has shown that the observed modification of parameters upon annealing can be described in terms of a two-layer model with two types of electrons—high and low mobility.     

Electrical Breakdown in Pure <Emphasis Type="Italic">n</Emphasis>- and <Emphasis Type="Italic">p</Emphasis>-Si

The results of calculations of the dependences of the kinetic coefficients of impact ionization and thermal recombination on an electric field in pure silicon are presented. By analogy with germanium, the dependences of the breakdown field Е_br on the material compensation ratio K are calculated. The validity of such calculation is justified in detail. The Е_br(K) curves are presented and compared with experimental data in the weak-compensation region. Matching with experimental results at which satisfactory agreement between theory and experiment is observed is performed.     

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.     

Sectoral transition between modes <Emphasis Type="Italic">H</Emphasis><Subscript>10</Subscript> and <Emphasis Type="Italic">H</Emphasis><Subscript>01</Subscript>

The excitation of main parasitic modes E ₁₁, H ₁₁, and H ₂₁, which have cutoff sections in a sectoral transition between modes H ₁₀ and H ₀₁, is investigated. It is shown that, for magnetic modes, including modes H ₁₁ and H ₂₁, it is unnecessary to use the Airy equation and that this circumstance simplifies the design relationships. The energies of these modes are calculated as functions of the transition parameters.     

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.     

<Emphasis Type="Italic">C-V</Emphasis> and <Emphasis Type="Italic">I-V</Emphasis> characteristics of ultrathin-oxide MOS structures: Identification and analysis

For an NMOS structure with 3.7-nm-thick oxide, dynamic I-V characteristics are digitally measured by applying an upward and a downward gate-voltage ramp. An averaging procedure is employed to deduce the tunneling (active) current component and the quasi-static C-V characteristic (CVC). Analyzing the depletion segment of the CVC provides reliable values of the semiconductor doping level, the oxide capacitance and thickness, and the sign and density of oxide-fixed charge, as well as estimates of the dopant concentration in the poly-Si region. These data are used to identify the Ψ_s(V _g), V _i(V _g), and I _t(V _i) characteristics, where Ψ_s is the n-Si surface potential, V _i is the voltage drop across the oxide, V _g is the gate voltage, and I _t is the tunneling current; the gate-voltage range explored extends to prebreakdown fields (～13 MV cm^?1). The results are obtained without recourse to fitting parameters and without making any assumptions as to the energy spectrum of electrons tunneling from the n-Si deep-accumulation region through the oxide. It is believed that experimental I _t-V _i and Ψ_s-V _g characteristics will provide a basis for developing a theory of tunneling covering not only the degeneracy and size quantization of the electron gas in the semiconductor but also the nonclassical profile of the potential barrier to electron tunneling associated with the oxide-fixed charge.     

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).     

<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.     

On the Significance of the Thermoelectric Figure of Merit <Emphasis Type="Italic">Z</Emphasis>

When the electrical conductivity, σ, thermal conductivity, λ, and thermopower, S, of a material are all assumed to be constant over the temperature range of interest, then the well-known thermoelectric (TE) figure of merit, Z = σS ²/λ, arises as part of the derivation of conversion efficiency in a TE generator. However, there are an infinite number of parameter sets (σ, λ, S) that yield any given Z. So, are they truly equivalent? This paper reviews the historical basis for Z as a metric for TE quality and discusses results of simulations on three systems having different parameter sets but the same Z. The three systems exhibit different power generation capabilities, illustrating that Z is not sufficient to specify the likely performance of a TE material in a system. Instead, a systems analysis is required that incorporates, at a minimum, source and sink temperatures and thermal resistances.     

Interphase interactions and features of structural relaxation in TiB<Subscript>x</Subscript>-<Emphasis Type="Italic">n</Emphasis>-GaAs (InP,GaP, 6<Emphasis Type="Italic">H</Emphasis>-SiC) contacts subjected to active treatment

The results of experimental studies of interphase interactions in TiB_x-n-GaAs (GaP, InP, 6H-SiC) contacts stimulated by external effects are described. These effects are rapid thermal annealing at temperatures as high as 1000°C, microwave treatment at f=2.5 GHz, and ⁶⁰Co γ radiation in the range of doses 10⁵–10⁷ rad. Possible thermal and athermal relaxation mechanisms of internal stresses are considered. It is shown that thermally stable TiB_x-n-GaAs (GaP, InP, 6H-SiC) interfaces can be formed.     

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.     

Influence of hydrogen sulfide on electrical and photoelectric properties of Al-<Emphasis Type="Italic">p</Emphasis>-Si-SnO<Subscript>2</Subscript>:Cu-Ag heterostructures

I-V characteristics, spectral photosensitivity, and the dependence of the photocurrent on bias, as well as the effect of a 1%-H₂S/N₂ gas mixture, were studied for an Al-p-Si-SnO₂:Cu-Ag heterostructure. The charge transport for carriers in the dark and under illumination was found to obey the law J ∝ U². Exposure to hydrogen sulfide results in a spectral shift of the photovoltage curve to shorter wavelengths. The kinetics of the decrease in photocurrent in a hydrogen sulfide medium is characterized by long relaxation times.     

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.     

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.