Papers by Keyword: Hole Concentration

Abstract: Photoresistors based on amorphous Si-Sn thin films (270-285 nm) with different concentration of tin were studied by spectral measurements of photoconductivity at room temperature and by low-temperature measurements of the Hall effect . Electrical contacts to the Si-Sn film was formed by aluminum layer deposition. When the Al contact is illuminated, the spectral sensitivity of the photoresistor with Sn consentration of 19% extends to 2060 nm due to Schottky barrier influence. It was proved that the Si-Sn alloy film provides photoresponse with cut-off energy of 0.98 eV that is close to the indirect band gap in the Si-Sn film. Three deep acceptor levels with activation energies of 90, 114, and 173 meV were found in the Si-Sn thin film (20% Sn) in the temperature range of 50 – 300 K. Sequential activation of the deep levels and their competition leads to a nonmonotonic change of the Si-Sn film conductivity (0.025 - 5.0 (Ω×cm)^-1) and mobility of holes (100 – 500 cm²/(V·s)). The transition to the intrinsic conductivity region of the amorphous Si-Sn film was not observed up to room temperature.

Abstract: Nitrogen - doped tin oxide (N-doped SnO₂) thin films were prepared on unheated glass substrate by dc magnetron sputtering of a Sn target in gas mixtures of O₂ and N₂. The N₂ flow rates were varied from 0 to 15 SCCM with the same working pressure of 1×10^-2 Torr. The as-deposited films were annealed in vacuum at 400 °C for 1 h. The films structure, electrical properties and optical properties were characterized by X-ray diffraction (XRD), 4-point probe and Hall effect measurement and portable fiber optic UV-vis spectrometer, respectively. The observed XRD patterns of films showed preferred (101) orientation of the SnO₂ tetragonal structure. The average crystalline size of the (101) diffraction peak decreased from 5.10 to 4.07 nm with N₂ flow rate increased. Hall measurement indicated that resistivity increased and carrier concentrations decreased as N₂ flow rate increased. The carrier concentrations decreased because N atoms substituted oxygen atom in SnO₂ lattice. The N atoms may forms acceptor level in SnO₂ band gap resulting in hole generation. The electron concentration from intrinsic defect were neutralized with the hole concentration. The carrier concentration decreased from 3.42×10¹⁷ cm^-3 for un-doped SnO₂ to the order of 10¹⁴ cm^-3. The average percent transmittance of un-doped SnO₂ of about 77.5% in visible range (400-700 nm) decreased to 60% with increasing N₂ flow rate. The optical band gap decreased from 3.64 eV for un-doped SnO₂ to 3.45 eV for N-doped SnO₂ films.

Abstract: The effect of Co-doping and thermal treatments on the superconducting properties of the heavily overdoped (Lu0.8Ca0.2)Ba2Cu3Oz has been investigated by X-ray diffraction, resistivity and thermoelectric power measurements. A comparative analysis of the resistivity and thermoelectric power of the (Lu0.8Ca0.2)Ba2(Cu3-xCox)Oz and the heat-treated Co-free (Lu0.8Ca0.2)Ba2Cu3Oz reveals that, in the overdoped region, the hole carriers reduced by the Co doping and by the oxygen depletion play a very similar role in the superconducting properties. As a result, a nearly common inverted parabolic correlation is observed between Tc and the planar carrier concentration determined from the room-temperature thermoelectric power measurements.