The temperature dependence of electrical conductivity and the photoconductivity of polycrystalline Cu 2 ZnSnS 4 were investigated. It was found that at high temperatures the electrical conductivity was dominated by band conduction and nearest-neighbour hopping. However, at lower temperatures, both Mott variable-range hopping (VRH) and Efros-Shklovskii VRH were observed. The analysis of electrical transport showed high doping levels and a large compensation ratio, demonstrating large degree of disorder in Cu 2 ZnSnS 4 . Photoconductivity studies showed the presence of a persistent photoconductivity effect with decay time increasing with temperature, due to the presence of random local potential fluctuations in the Cu 2 ZnSnS 4 thin film. These random local potential fluctuations cannot be attributed to grain boundaries but to the large disorder in Cu 2 ZnSnS 4 .the CZTS absorber layer and the Mo back contact have been pointed out as factors that reduce the solar cell efficiency [4,5]. Strong research efforts have been made in the study of different CZTS synthesis routes [3][4][5][6][7][8][9][10], CZTS structural and optical properties [2,[6][7][8], as well as in the development of CZTS solar cells [3-5, 9, 10]. However, very little is known about the electrical transport and photoconductivity properties of CZTS thin films and further studies are required.The study of the temperature dependence of electrical transport in semiconductor materials is very important for the knowledge of material parameters, the understanding of the transport and microscopic mechanisms of charge transfer, as well as for the optimization and design of solar cells. Very recently, we have shown that the radiative and non-radiative recombination mechanisms in CZTS thin films are strongly

Lanthanide orthoantimonates represented by the chemical formula LnSbO4 (Ln are all the lanthanides elements with exception of cerium and promethium) were synthesized via solid-state reactions. The crystalline structures of LnSbO4 were determined by high-resolution Synchrotron X-ray diffraction and the Rietveld method. The samples exhibited monoclinic structures with two different arrangements as a function of the ionic radius of the lanthanide metal. For compounds with the largest ionic radii (Ln = La and Pr), the P21/n space group was determined, while compounds with intermediate and smallest ionic radii (Ln = Nd–Lu) were described under the P21/c setting. Raman spectroscopy was employed to study the vibrational features of all compounds, allowing us to determine the characteristic phonons for each structure and, consequently, to establish the relationship between chemical environment and vibrational properties. Optical features of typical SmSbO4 and TbSbO4 were thoroughly investigated, and the results indicate that the orthoantimonates are promising luminescent inorganic materials. The photoluminescence spectra (emission and excitation) of both compounds were obtained as a function of temperature under ultraviolet radiation, showing strong orange (Sm) and green (Tb) emissions, respectively. Chromaticity diagrams (CIE) were also determined for all LnSbO4 series, aiming to bring forward the color coordinates for these emitters tuned by the chemical environment and temperature.

The electronic transport properties of several Mg-doped GaAs nanowires are investigated. It is shown that Mg can be successfully used as a nontoxic and noncarcinogenic p-type dopant in GaAs nanowires. The doping levels, expanding over two orders of magnitude, and free holes mobility in the NW were obtained by the analysis of field effect transistors transfer curves. The study of the temperature dependence of the electrical resistivity of the nanowires shows that electronic transport changes from conduction of free holes, above room temperature, to variable hopping conduction at lower temperatures. Both, Mott and Efros-Shklovskii variable range hopping mechanism were clearly identified in the nanowires.

The electrical transport properties of individual Mg doped GaAs nanowires are investigated. It is shown that Mg can be successfully used as a nontoxic p-type dopant in GaAs nanowires. The doping levels, expanding over two orders of magnitude, and free holes mobility in the NW were obtained by the analysis of field effect transistors transfer curves. The temperature dependence of the electrical resistivity above room temperature shows that the polytypic structure of the NWs strongly modifies the NWs charge transport parameters, like the resistivity activation energy and holes mobility. At lower temperatures the NWs exhibit variable range hopping conduction. Both Mott and Efros-Shklovskii variable range hopping mechanisms were clearly identified in the nanowires.