Advanced Materials Research Vol. 1117

Abstract: The Seebeck coefficient of P-doped ultrathin Si-on-insulator (SOI) layers is investigated for the application to a highly-sensitive thermopile infrared photodetector. It is found that the Seebeck coefficient originating from the phonon drag is significant in the lightly doped region and depends on the carrier concentration with increasing carrier concentration above ~5×10¹⁸ cm^-3. On the basis of Seebeck coefficient calculations considering both electron and phonon distribution, the phonon-drag part of SOI Seebeck coefficient is mainly governed by the phonon transport, in which the phonon-phonon scattering process is dominant rather than the crystal boundary scattering even in the SOI layer with a thickness of 10 nm. This fact suggests that the phonon-drag Seebeck coefficient is influenced by the phonon modes different from the thermal conductivity.

Abstract: Photosensitivity light intensity dependence of holographic grating recording in three azobenzene molecular glassy films (denoted as WE-3, ZWK-3, ZWK-2TB) and in one chalcogenide glassy film As₄₀S₁₅Se₄₅ (As-S-Se) has been experimentally studied in the intensity range from 0.0034 to 1.13 W/cm² at 633 nm. It is found that photosensitivity increases when recording light intensity is increased. The physical reasons are discussed and a simple mathematical model is given explaining the obtained results.

Abstract: We investigate thermoelectric characteristics of SiGe nanostructures for realizing high-sensitive infrared photodetector applications. In this paper, for future Ge and SiGe nanowires, we fabricate p-type Ge-on-insulator (GOI) substrates by a direct wafer bonding process. We discuss the annealing effect on the GOI substrate in the process and measure its Seebeck coefficient in the temperature range of 290-350 K. The Seebeck coefficient of the GOI layers is almost identical with the reported values for Ge. This result confirms that the measured Seebeck coefficient of GOI layers is not influenced by the buried oxide (BOX) layer and the Si substrate.

Abstract: Kim et al. suggest that replacing ZnO particle with ZnO vertically aligned nanorods shows much higher energy conversion efficiency [1]. The difference between nanoparticles and nanorods can be seen on figure 1. Yet, vertically aligned nanorods can be grown through the difficult and expensive methods. Pomar et al. reported the growing through atomic layer deposition (ALD) method [2]. Jeong et al. grew the vertically aligned nanorods using metal-organic chemical vapor deposition (MOCVD) method with really high temperature (700-900oC) [3]. When the nanorods are applied for DSSCs, synthesizing really fine nanorods is not necessary. Lee et al. managed to grow nanorods on the seed layer for DSSC application which was post-annealed at 500-600oC [4]. Hu et al. reported vertically aligned nanorods using low temperature chemical bath method, but the deposition time is between 3 hours and 6 days [5].

Abstract: Low temperature photoluminescence (PL) of high-resistivity detector-grade Cl-compensated CdTe semiconductor crystals subjected to irradiation with nanosecond (τ = 7 ns) laser pulses of the second harmonic (λ = 532 nm) of a YAG:Nd laser is studied. Irradiation of CdTe crystals within the certain range of laser pulse energy densities results in a relative decrease in the emission intensity in both the deep energy level and edge regions and an increase in the exciton band intensity in the PL spectra. The evolution of the PL spectra depending on laser energy density, excitation level and temperature under excitation are analyzed. Laser-stimulated transformation of the point defect structure of the CdTe surface region and mechanisms of laser-induced defect formation are discussed. The optimal regimes of laser processing have been obtained which result in the minimum ratio of the defect and exciton bands that is an evidence of an increase in the structural perfection of the irradiated crystals.

Abstract: Semiconductor Hg₃In₂Te₆ crystals and their analogous are solid solutions of In₂Te₃ and HgTe. Hg₃In₂Te₆ crystals are congruently melted as chemical compound. Like In₂Te₃ the Hg₃In₂Te₆ crystal has cubic crystal lattice with stoichiometric vacancies in their crystal structure. The electroconductivity, photoconductivity, mechanical, chemical properties of the crystals do not deteriorate after their irradiation by γ-photons with energies up to 1 MeV and doses up to 10¹⁸ cm^-2 , by electrons with energies up to 300 MeV and doses up to 10¹⁹ cm^-2 and by mixed reactor irradiation (filtered slow neutrons) with doses up to 10¹⁹ cm^-2 [1,2]. This feature is determined by high concentration (~10²¹ cm^-3) of stoihiometric vacancies (V_s) in crystal structure, where every third In-cation node is empty. These V_s are electroneutral, they capture all impurity atoms in these crystals and kept them in electroneutral state too. On the other hand this feature doesn't allow to form direct p-n junctions in these crystals by introducing the impurities. However, we have developed p-n junction analogues in form of Schottki diodes and corresponding photodiodes with semitransparent metal layer on single crystal Hg₃In₂Te₆ substrate that allows irradiation to get into active region preserving this way all the advantages compared to p-n junction.

Abstract: The photo current-voltage characteristic of a solar cell with graded band gap is calculated numerically based on the drift-diffusion equation and Poisson equation. The calculated efficiency of the CdTe solar cell with p-n junction located in 1μm depth increases remarkably when the band gap of the front n-type layer is graded. The effect is strong for high surface recombination velocity and is remarkable even at: the calculated efficiency increases from 19.6% to 24.3%.

Abstract: We have developed a continuous wave THz Signal Generator on the principle of Difference Frequency Generation in a GaP crystal and constructed a high accurate CW THz spectrometer using it as a light source. Combining with a bolometer detector cooled by a mechanical cooler, the spectrometer is now working as non-stop system. Increasing the power of CW THz wave up to 100 nW, uncooled detector or camera is now available. This is the first report of CW THz beam observation generated at the surface of GaP crystal.

Abstract: In the present paper, we study electromagnetic properties of single-turn, double-turn and DNA-like helices in microwave range. In particular, we determine the magnetic flux density in the center of the inclusions and their inductance and capacitance. In this paper we have numerically obtained the magnetic field of different kinds of helices: the single-turn helical element, the double-turn helical element, the half-turn helical element and DNA-like helical element. For these helical elements the inductance, capacitance and Q factor were calculated numerically.

Abstract: The paper presents first stage of research for numerical modelling of heat exchange in counterflow shell-type system with variable dimensions, which is partly placed under the ground level. Mathematical model of heat and mass balance is reduced to 1D case to make numerical calculation faster. Different kinds of boundary conditions (surface temperature, convection) and various physical properties of layer between pipes (from non-insulated to well insulated) are used to check the usability of created model.