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1.
The Shubnikov–de Haas effect and the Hall effect in n-Bi2–xTlxSe3 (x = 0, 0.01, 0.02, 0.04) and p-Sb2–xTlxTe3 (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-Bi2–xTlxSe3 and increases the electron mobility. In p-Sb2–xTlxTe3, both the hole concentration and mobility decrease upon Tl doping. The change in the crystal defect concentration, which leads to these effects, is discussed.  相似文献   

2.
A quantitative theory of the diagonal (ballistic) and nondiagonal (shift) band index contributions to the two-photon current of the linear photovoltaic effect in a semiconductor with a complex band due to the asymmetry of events of electron scattering at phonons and photons is developed. It is shown that processes caused by the simultaneous absorption of two photons do not contribute to the ballistic photocurrent in n-GaP. This is due to the fact that, in this case, there is no asymmetric distribution of the momentum of electrons excited with photons; this distribution arises upon the sequential absorption of two photons with the involvement of LO phonons. It is demonstrated that the temperature dependence of the shift contribution to the two-photon photocurrent in n-GaP is determined by the temperature dependence of the light-absorption coefficient caused by direct optical transitions of electrons between subbands X1 and X3. It is shown that the spectral dependence of the photocurrent has a feature in the light frequency range ω → Δ/2?, which is related to the hump-like shape of subband X1 in n-GaP1 and the root-type singularity of the state density determined as kω-1= (2?ω–Δ)–1/2, where Δ is the energy gap between subbands X1 and X3. The spectral and temperature dependences of the coefficient of absorption of linearly polarized light in n-GaP are obtained with regard to the cone-shaped lower subband of the conduction band.  相似文献   

3.
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 VOC = 0.52 V, the short-circuit current is ISC = 0.265 mA/cm2, and the fill factor is FF = 0.39.  相似文献   

4.
Electrical and thermoelectric properties of a lightly doped n-Bi2Te2.7Se0.3 solid solution have been studied in the temperature range 77–300 K. The results are compared with data for the compound PbTe0.9Se0.1 with a similar magnitude of the Seebeck coefficient S at 84 K. Along with lower thermal conductivity, Bi2Te2.7Se0.3 has a higher electrical conductivity σ and a much weaker temperature dependence. As a result, the power coefficient S 2σ in optimal samples begins to decrease only when the density of minority carriers becomes significant. In this case, |S| considerably exceeds the standard value of 200 μV/K. The reduction of the electron density reduces the thermoelectric figure of merit Z at its maximum and slightly lowers the temperature of the maximum; therefore, the expected effect on the average value of Z in the range 77–300 K is absent. Similar behavior is observed in Bi2Te2.88Se0.12, although the effect is less pronounced. The experimental results are discussed taking into account possible changes in the dominant scattering mechanisms, carrier density, and electron energy spectrum. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 7, 2004, pp. 811–815. Original Russian Text Copyright ? 2004 by Konstantinov, Prokof’eva, Ravich, Fedorov, Kompaniets.  相似文献   

5.
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.  相似文献   

6.
The magnetic-field dependences of the Hall coefficient and transverse magnetoresistance are studied experimentally and theoretically in p-Bi2Te3 crystals doped heavily with Sn and grown by the Czochralski method in the case of both classical and quantizing magnetic fields as high as 12 T with the magnetic-field orientation along the C 3 trigonal axis. The Shubnikov-de Haas effect and quantum oscillations of the Hall coefficient were measured at temperatures of 4.2 and 11 K. The six-ellipsoid Drabble-Wolfe model of the energy spectrum and the magnetic-field dependence of the Hall coefficient are used as the basis for the method for determining the Hall factor and Hall mobility. New evidence is obtained in support of the existence of the narrow band of impurity Sn states occupied partially with electrons against the background of the light-hole band spectrum. The parameters of impurity states are estimated including their energy (E Sn ≈ 15 meV), the broadening (Γ « kT), and the radius of localization of the impurity state (R ≈ 30 Å).  相似文献   

7.
The temperature and magnetic-field dependences of the galvanomagnetic properties of n-Bi2Te3 heteroepitaxial films in magnetic fields to 14 T at low temperatures are studied. It is shown that steps in the magnetic-field dependences of the quantum Hall effect and the plateau in the temperature dependences of the magnetoresistance of films are caused by topological surface states of Dirac fermions.  相似文献   

8.
Resonant micro-Raman spectra and the morphology of the interlayer Van der Waals surface are studied for layered thin films of n-Bi2Te3 and solid solutions based on Bi2Te3. It is found that the composition, thickness, surface morphology, and the method of obtaining films affect the relative intensity of Raman phonons, which are sensitive to the topological surface states of Dirac fermions.  相似文献   

9.
The reflectance spectra of a p-Bi2Te3:Sn crystal are recorded in the range 50–7900 cm–1. The spectra possess features characteristic of charge-carrier plasma oscillations and a contribution of phonons. It is shown that the dielectric function that is used in the context of Drude–Lorentz theory and includes the contributions of hole plasma oscillations and two phonons adequately describes the experimental data obtained at room temperature and at a temperature of T = 78 K.  相似文献   

10.
The amplitude-frequency modulation of oscillations of the magnetoresistance of 2D electrons in an AlSb(δ-Te)/InAs/AsSb(δ-Te) quantum well is studied. In the dependence of the amplitude of the oscillations δ(1/B) T = const, regions of negative Dingle temperature are observed. The anomalies in the dependence δ(1/B) T = const are attributed to the fact that the quantizing magnetic field resonantly induces intersubband electron-electron interaction between the 2D electrons of the ground size-quantization subband and excited subband. The resonance fields B and the times corresponding to the collision-related broadening of the Landau levels are estimated. The concentration threshold of filling of the excited size-quantization subband is established at a level of n s ≈ 8 × 1011 cm?2.  相似文献   

11.
A junction device has been fabricated by growing p-type Bi2Te3 topological insulator (TI) film on an n-type silicon (Si) substrate using a thermal evaporation technique. Annealing using different temperatures and durations was employed to improve the quality of the film, as confirmed by microstructural study using x-ray diffraction (XRD) analysis and atomic force microscopy (AFM). The pn diode characteristics of the junction devices were studied, and the effect of annealing investigated. An improved diode characteristic with good rectification ratio (RR) was observed for devices annealed for longer duration. Reduction in the leakage or reverse saturation current (\( I_{\rm{R}} \)) was observed with increase in the annealing temperature. The forward-bias current (\( I_{\rm{F}} \)) dropped in devices annealed above 400°C. The best results were observed for the sample device annealed at 450°C for 3 h, showing figure of merit (FOM) of 0.621 with RR ≈ 504 and \( I_{\rm{R}} \) = 0.25 μA. In terms of ideality factor, the sample device annealed at 550°C for 2 h was found to be the best with \( n \) = 6.5, RR ≈ 52.4, \( I_{\rm{R}} \) = 0.61 μA, and FOM = 0.358. The majority-carrier density \( \left( {N_{\rm{A}} } \right) \) in the p-Bi2Te3 film of the heterojunction was found to be on the order of 109/cm3 to 1011/cm3, quite close to its intrinsic carrier concentration. These results are significant for fundamental understanding of device applications of TI materials as well as future applications in solar cells.  相似文献   

12.
On the basis of investigations of the temperature and concentration dependences of kinetic coefficients (the Hall coefficientR, the electrical conductivity σ, and thermopower α0) in n-type Ag2Te, it is established that Ag atoms in Ag2Te create the shallow donor levels located at a distance of (0.002?7 × 10?5 T) eV from the bottom of the conduction band. It is shown that silver telluride has n-type conductivity starting with the deficiency of Ag ≥ 0.01 at % in the stoichiometric composition, and it is practically impossible to achieve the stoichiometric composition in Ag2Te.  相似文献   

13.
The fine structure of the long-wavelength edge of the polarization spectra of exciton-phonon absorption in moderate-purity n-type 6H-SiC crystals with a concentration of uncompensated donors ND?NA=(1.7–2.0)×1016 cm?3 at T=1.7 K was studied. The analysis of new special features found at the absorption edge and the reliable detection of the onset of exciton-phonon steps related to the emission of phonons from acoustical and optical branches allowed highly accurate determination of a number of important parameters such as the band gap, the exciton band gap, the exciton binding energy, and the energies of spin-orbit and crystal-field splitting of an exciton. For the first time, transitions with the emission of LA phonons to the 1S exciton state with an M1-type dispersion law were detected in EZ(C) polarization (the electric-field vector is parallel to the optical axis of the crystal). This observation supports the previously predicted “two-well” structure of the conduction band minimum in 6H-SiC.  相似文献   

14.
Spectra of edge photoluminescence (PL) at 300 K have been studied in a set of Czochralski-grown Te-doped GaAs single crystals with a free carrier density of n0=1017–1019 cm?3. The carrier density dependences of the chemical potential and band gap narrowing are obtained by analyzing the PL spectral line profiles. The dependence of the effective mass of electrons at the bottom of the conduction band on their density, m 0 * (n0), is calculated. It is shown that the nonmonotonic m 0 * (n0) dependence correlates with data on electron scattering in the material under study and results from the ordering of impurity complexes.  相似文献   

15.
The results of investigations of electrical, optical, and photoelectric properties of CdIn2Te4 crystals, which were grown by the Bridgman method are presented. It is shown that electrical conductivity is determined mainly by electrons with the effective mass mn = 0.44m0 and the mobility 120–140 cm2/(V s), which weakly depends on temperature. CdIn2Te4 behaves as a partially compensated semiconductor with the donor-center ionization energy Ed = 0.38 eV and the compensation level K = Na/Nd = 0.36. The absorption-coefficient spectra at the energy < Eg = 1.27 eV are subject to the Urbach rule with a typical energy of 18–25 meV. The photoconductivity depends on the sample thickness. The diffusion length, the charge-carrier lifetime, and the surface-recombination rate are determined from the photoconductivity spectra.  相似文献   

16.
The Hall factor and thermoelectric properties of an n-Bi2Te2.7Se0.3 solid solution with the roomtemperature Seebeck coefficient |S| = 212 μV/K have been studied in the temperature range 77–350 K. The observed temperature dependences demonstrate a number of specific features, which were earlier found in samples with a lower electron density N. The effect of these specific features on the thermoelectric figure of merit Z appears to be more favorable for the sample under study: this sample is most efficient in the temperature range 120–340 K, and the average value of ZT is 0.71. It is found that a rise in the density N enhances the factor responsible for the effective mass decreasing as the temperature increases. This effect appears when the analysis is carried out in terms of a single-band parabolic model with N = const(T). This finding suggests that the most probable reason for the unusual behavior of these properties is the complex structure of the electron spectrum. Temperature dependences obtained from calculations of the transport coefficients show good agreement with the experimental data for two samples of the mentioned composition with different electron densities. The calculations have been performed in terms of a two-band model and an acoustic scattering mechanism and take into account the anisotropy and nonparabolicity of the light-electron spectrum.  相似文献   

17.
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 IV 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.  相似文献   

18.
Self-consistent calculations of the Rashba splitting both in inversion and accumulation InAs layers were carried out using a method based on reducing 6×6 and 8×8 Kane matrix equations to a Schrödinger-type equation. Disregarding the Γ7-band contribution yielded a splitting magnitude overestimated by 50%. The essentially nonlinear dependence of splitting on the two-dimensional (2D) wavevector k restricts the applicability of the Rashba parameter α (coefficient at the k-linear term in the spectrum), including its value at the Fermi level, because of a strong dependence of the latter on the approximations applied to the two-dimensional spectrum. The relative differences Δn/n of the spin-split subband populations, calculated for the inversion layer, were found to be 2–3 times lower than those measured by Matsuyama et al. (see text). The experimental study of accumulation InAs layers showed that the corresponding value Δn/n does not exceed the calculated one, ~0.02. The approach employed to describe the 2D spectrum (including spin-orbit splitting) was also shown to be adequate when applied to the case of quasi-classical quantization in a classically self-consistent surface potential.  相似文献   

19.
The mechanical strains and densities of surface charge states in GaAs layers grown by low-temperature (LT) molecular-beam epitaxy on Si(100) and GaAs(100) substrates are investigated by photoreflectance spectroscopy. Lines corresponding to the fundamental transition (E g ) and the transition between the conduction band and spin-orbit-split valence subband (E g + Δ SO ) in GaAs are observed in the photoreflectance spectra of Si/LT-GaAs structures at 1.37 and 1.82 eV, respectively. They are shifted to lower and higher energies, respectively, relative to the corresponding lines in GaAs/LT-GaAs structures. Comparing the spectra of the Si/LT-GaAs and GaAs/LT-GaAs structures, it is possible to estimate mechanical strains in LT-GaAs layers grown on Si (by analyzing the spectral-line shifts) and the density of charge-carrier states at the GaAs/Si heterointerface (by analyzing the period of Franz–Keldysh oscillations).  相似文献   

20.
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.  相似文献   

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