Calculation of the Schottky barrier and current–voltage characteristics of metal–alloy structures based on silicon carbide

A simple but nonlinear model of the defect density at a metal–semiconductor interface, when a Schottky barrier is formed by surface defects states localized at the interface, is developed. It is shown that taking the nonlinear dependence of the Fermi level on the defect density into account leads to a Schottky barrier increase by 15–25%. The calculated barrier heights are used to analyze the current–voltage characteristics of n-M/p-(SiC)_1–x(AlN)_x structures. The results of calculations are compared to experimental data.     

Features of the Current Flow in Injection Structures Based on PbSnTe:In Films

This paper reports a study of the current–voltage (I–V) features of the p-i-p structures based on Pb_1–xSn_xTe:In films with the tin content х ≈ 0.31 in which the metal–insulator transition occurs. It is shown that the photocurrent is the hole current under light interband excitation, and electron trapping is dominant. The experimental and theoretical data are compared.     

Effect of thallium doping on the mobility of electrons in Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> and holes in Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>

The Shubnikov–de Haas effect and the Hall effect in n-Bi_2–xTl_xSe₃ (x = 0, 0.01, 0.02, 0.04) and p-Sb_2–xTl_xTe₃ (x = 0, 0.005, 0.015, 0.05) single crystals are studied. The carrier mobilities and their changes upon Tl doping are calculated by the Fourier spectra of oscillations. It is found shown that Tl doping decreases the electron concentration in n-Bi_2–xTl_xSe₃ and increases the electron mobility. In p-Sb_2–xTl_xTe₃, both the hole concentration and mobility decrease upon Tl doping. The change in the crystal defect concentration, which leads to these effects, is discussed.     

Matrix-type effect on the magnetotransport properties of Ni–AlO and Ni–NbO composite systems

The effect of the insulating-matrix material on the electronic and magnetic properties of nanocomposites is investigated in the Ni_x(Al₂O₃)_100–x metal–insulator system and the Ni_x(Nb₂O₅)_100–x metal–semiconductor system. It is established that the characteristics of composites determined by electron transport through the matrix (the electrical resistivity, the position of the electrical percolation threshold, the magnetoresistance effect) depend on the material type. Replacement of the matrix from Al₂O₃ to Nb₂O₅ results in a decrease in the electrical resistivity by two–three orders of magnitude, a decrease in the magnetic resistivity by more than an order of magnitude, and in displacement of the percolation threshold from 40 to 30 at % of Ni. In this case, the magnetic properties of the composites are independent of the type of matrix: the concentration of the magnetic percolation threshold is identical in the two systems (~45 at % of Ni), and the coercive force of the samples occurring beyond the percolation threshold is close in magnitude (5–8 and 12–18 Oe) in the Ni_x(Nb₂O₅)_100–x and Ni_x(Al₂O₃)_100–x composites, respectively.     

On the photoconductivity of TlInSe<Subscript>2</Subscript>

The current–voltage (I–V) and photocurrent–light intensity (I _pc –Φ) characteristics and the photoconductivity relaxation kinetics of TlInSe₂ single crystals are investigated. Anomalously long relaxation times (τ ≈ 10³ s) and some other specific features of the photoconductivity are observed, which are explained within the barrier theory of inhomogeneous semiconductors. The heights of the drift and recombination barriers are found to be, respectively, E _dr ≈ 0.1 eV and E _r ≈ 0.45 eV.     

On the preparation and photoelectric properties of Tl1–x In1–x Sn x Se2 (x = 0.1–0.25) alloys

The technological conditions for growing single crystals of Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys are developed. The spectral distribution of the photoconductivity of the grown crystals at T = 300 K and thermally stimulated conductivity are studied. The effect of In³⁺cation substitution with Sn⁴⁺ in Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys on their photoelectric properties is shown.     

Mobility of minority charge carriers in <Emphasis Type="Italic">p</Emphasis>-HgCdTe films

Temperature dependences of electron mobility in p-Hg_1?xCd_xTe films (x=0.210–0.223) grown by molecular beam epitaxy are investigated. In the temperature range 125–300 K, mobility was found by the mobility-spectrum method, and for the range 77–125 K, it was found using a magnetophotoconductivity method suggested in this study. The method is based on the measurement of the magnetic-field dependence of photoconductivity. The magnetic field is parallel to the radiation and normal to the sample surface. The electron mobility is determined using the simple expression μ _n [m²/(V s)]=1/B _H [T]. Here, B _H is the induction of the magnetic field corresponding to a half-amplitude of the photoconductivity signal under zero magnetic field. In the temperature range 100–125 K, the results obtained by the magnetophotoconductivity and mobility-spectrum methods coincide. For the samples investigated, the electron mobility at 77 K is in the range 5–8 m²/(V s).     

Magnetotransport properties of nonstoichiometric Si–Mn alloys with an excess of manganese relative to silicides Mn<Subscript>4</Subscript>Si<Subscript>7</Subscript> and MnSi

Comparative examination of magnetotransport properties of nonstoichiometric Si_1–x Mn _x alloys with roughly the same (δх/x ≈ 7%) excess of Mn relative to silicides Mn₄Si₇ and MnSi has been performed. Films of Si_1–x Mn _x (х ≈ 0.39 and 0.535) with a thickness of 60–70 nm have been fabricated by means of pulsed laser deposition on Al₂O₃ (0001) substrates at a temperature of 340°С. It has been found that the excess of Mn produces the strongest effect on the Curie temperature in the case of MnSi (Т _С increases from 30 K to 300 K and higher), while no such effect is observed in Mn₄Si₇. This may be attributed to strong nonmagnetic disorder in Si_1–x Mn _x with x ≈ 0.39 and the associated unusual behavior of negative magnetoresistance (NMR): The NMR varies linearly with magnetic field at В ≤ 1.3 T and exhibits almost no temperature dependence at T = 40–85 K.     

Schottky-Barrier Model Nonlinear in Surface-State Concentration and Calculation of the <Emphasis Type="Italic">I–V</Emphasis> Characteristics of Diodes Based on SiC and Its Solid Solutions in the Composite Charge-Transport Model

A modified Schottky-barrier model, which is nonlinear in terms of the surface-state concentration and contains a local quasi-Fermi level at the interface induced by excess surface charge, is proposed. Such an approach makes it possible to explain the observed similarity of the I–V characteristics of diodes with the Schottky barrier M/(SiC)_1–x(AlN) _x and those of heterojunctions based on SiC and its solid solutions taking into account Φ_g ≈ Φ_B. The results of calculations of the Schottky-barrier heights are consistent with the experimental data obtained from measurements of the photocurrent for metals (M): Al, Ti, Cr, and Ni. The I–V characteristics in the composite–additive model of charge transport agree with the experimental data for the n-M/p-(SiC)_1–x(AlN) _x and n-6H-SiC/p-(SiC)_0.85(AlN)_0.15 systems.     

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.     

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.     

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.     

Energy spectrum of charge carriers in TlIn<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>Yb<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>Te<Subscript>2</Subscript> solid solutions

The temperature dependences of the electrical conductivity σ(T), the Hall coefficient R(T), and the thermoelectric coefficient α(T) are investigated in TlIn_1–xYb_xTe₂ (0 < x < 0.10) solid solutions at 80–1000К. From the kinetic parameters, the effective masses of electrons and holes are determined. The obtained experimental data on σ(T) and α(T) are interpreted within the context of a model with one and two types of charge carriers. It is established that, since x = 0.05, the TlIn_1–xYb_xTe₂ solid solutions belong to the class of narrow-gap semiconductors that have high matrix elements of interaction.     

Leakage currents over the Surface of CdHgTe-based photodiodes

The leakage current I _p over the surface of Cd_xHg_1−x Te-based photodiodes that have a cutoff wavelength of the photosensitivity spectrum of λ=9.8–11.6 μm and are fabricated by implanting Zn⁺⁺ ions into the p-type solid solution is investigated. The surface character of the I _p current is indicated by a coordinate shift of the peak in the sensitivity profile of n ⁺-p junctions, which is measured in a scanning mode by the beam of a CO₂ laser with a wavelength of 10.6 μm, with an increase in voltage U across the photodiode and the shift of spectral characteristics to shorter wavelengths with increasing U. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 7, 2004, pp. 890–895. Original Russian Text Copyright ? 2004 by Biryulin, Turinov, Yakimov.     

Investigation of the ZnS-CdHgTe interface

The ZnS-Cd_xHg_1?xTe interface was investigated using the capacitance-voltage characteristics of MIS structures in experimental samples. During fabrication of the n⁺-p junctions based on p-Cd_xHg_1?xTe, the density of states within the range N _ss =(1–6)×10¹¹ cm^?2 eV^?1 at T=78 K was obtained. The experiments showed that the conditions in which n⁺-p junctions are fabricated only slightly affect the state of the ZnS-CdHgTe interface. The negative voltages of the at bands V _FB , even if immediately after deposition of the ZnS films V _FB >0, point to the enrichment of the ZnS-p-CdHgTe near-surface layer with majority carriers, specifically, holes. This led to a decrease in the leakage current over the surface. During long-term storage (as long as ～15 years) in air at room temperature, no degradation of differential resistance R _d , current sensitivity S _i , and detectivity D* of such n⁺-p junctions with a ZnS protection film was observed.     

Effective electron mass in a Mn<Subscript>x</Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te system

The reflection spectra of n-Mn_xHg_1?xTe single crystals and epitaxial layers were measured at 300 K. The effective electron mass was determined for the samples with x=0.06–0.10 and an electron concentration N>6×10¹⁶ cm^?3. The calculated values of effective electron mass are close to experimental values.     

Relaxation of excitons in semimagnetic asymmetric double quantum wells

The steady-state circular-polarized photoluminescence in semimagnetic asymmetric double quantum wells based on Cd(Mn,Mg)Te is studied thoroughly in relation to the polarization of intrawell nonresonance photoexcitation in magnetic fields Bup to 9 T. In low fields B, in which the exciton in the magnetic well is higher in energy than the exciton in the nonmagnetic well, the complete interwell relaxation of excitons is observed. In fields higher than B _c = 3–6 T, at which the exciton level in the magnetic well crosses the field-independent exciton level in the nonmagnetic well, the magnetic-field-induced red shift of the exciton in the magnetic well is accompanied by the establishment of a nonequilibrium distribution of excitons. This suggests that spin relaxation plays an important part in the interwell separation of excitons in the spin-dependent potential of the heterostructure. The efficiency of spin relaxation is controlled by mixing of valence band states in the nonmagnetic well and by splitting of heavy and light holes Δ _hh-lh . Different modes of interwell tunneling are observed in different field regions separated by the field B _c ^* > B _c corresponding to the crossing of the localized excitons in the nonmagnetic well and free excitons in the magnetic well. Possible mechanisms of interwell tunnel relaxation are discussed.     

Effect of anion and cation substitution in tungsten disulfide and tungsten diselenide on conductivity and thermoelectric power

The temperature dependences of the conductivity and thermoelectric power for a series of samples W_1–x Nb _x S₂, W_1–x Nb _x Se₂, WS_2–y Se _y , W_1–x Nb _x S_2–y Se _y are studied at low temperatures. It is found that the cation substitution of W atoms with Nb leads to an increase in the conductivity and a decrease in the thermoelectric power. The anion substitution of S with Se atoms results in a simultaneous increase in the conductivity and thermoelectric power. The highest power factor among the samples studied is inherent to W_0.8Nb_0.2Se₂.     

Dielectric Properties of (Bi<Subscript>0.5</Subscript>K<Subscript>0.5</Subscript>)ZrO<Subscript>3</Subscript> Modified (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> Ceramics as High-Temperature Ceramic Capacitors

(1???x)K_0.5Na_0.5NbO₃-x(Bi_0.5K_0.5)ZrO₃ [abbreviated as (1???x)KNN-xBKZ, 0?≤?x?≤?0.08] lead-free ceramics have been fabricated by a solid-state processing route. Based on the x-ray diffraction data and temperature-dependent dielectric characteristics, an orthorhombic phase for x?≤?0.03 and single rhombohedral one for x?≥?0.05 at room temperature were determined. The cell volume firstly increases, then decreases and finally increases with increasing BKZ, depending on ionic size and crystallographic structure. For the sample of x?=?0.05, a temperature-stable high permittivity (~?1736?±?15%) along with low dielectric loss tangent (≤?5%) is recorded from 158°C to 407°C. In addition, the activation energies of dielectric relaxation and dc conductivity at high temperatures were characterized by impedance spectroscopy. A combined effect of lattice distortion and oxygen vacancies on the magnitude of activation energies was discussed.