INVESTIGATION OF PROPERTIES OF N-TINISN SEMICONDUCTOR DOPED WITH NB DONOR IMPURITY

Abstract

The electrokinetic and energetic characteristics of the semiconductive Ti_1-xNb_xNiSn solid solution were investigated in the ranges Т=80–400 К, х=0–0.10. Samples were prepared using an electric arc furnace by direct melting of the constituent elements under a purified argon atmosphere (porous Ti was used as a getter). The alloys were annealed at 1 073 K for 720 hours and quenched in cold water. Phase analysis was performed using X-ray powder diffraction patterns of the synthesized samples. The elemental and phase compositions of synthesized samples were examined by Scanning Electron Microscopy (SEM) using Tescan Vega 3 LMU scanning microscope. Microprobe analysis of the concentration of atoms on the surface of Ti_1‑xNb_xNiSn samples, including х=0–0.10, established their correspondence to the initial compositions of the alloys, and X-ray phase and structural analyzes showed no traces of extraneous phases on the diffraction patterns except for the main phase indexed in the MgAgAs structure type.

The temperature dependences of electrical resistivity (ρ(Т)) were measured employing a two-probe method on a millimeter-scale, well-shaped pieces cut by spark erosion from the polycrystalline samples in the temperature range 80–400 K. Thermopower coefficient (α) was measured in relation to the pure copper in the temperature range 80–400 K.

The results of the study of the electrical resistivity ρ and the thermopower coefficient α of the origin n-TiNiSn semiconductor are consistent with the previously obtained results [1], and the dependences of ln(ρ(1/T)) and α(1/T) are characteristic of semiconductors.

Introducing the lowest concentration of the donor impurity Nb to the n-TiNiSn electronic conductivity semiconductor radically changes the behavior of the temperature dependences of the electrical  resistivity ρ(T,х)  and  the  thermopower  coefficient α(T,x) of Ti_1-xNb_xNiSn solid solution. For all Ti_1-xNb_xNiSn samples, at concentrations x>0, the activation parts disappear on the temperature dependencies of the electrical resistivity. At the same time, the values of the electrical resistivity ρ(T,x) only increase with increasing temperature, which indicates the metallization of electrical conductivity, and the thermopower coefficient retains its sign. This means that the concentration x=0.01 of the Nb donor impurity is sufficient for the Fermi level to move from the band gap of Ti_1-xNb_xNiSn to the conduction band.

The study of Ti_1-xNb_xNiSn solid solution, synthesized by doping n-TiNiSn with Nb atoms by substituting Ti atoms in the crystallographic position 4a, showed that the obtained thermoelectric material has a high efficiency of converting thermal energy into electrical energy.

Keywords: electrical conductivity, thermopower coefficient, Fermi level, structural defect.