Effects of Ge Doping on the Charge Transport and Thermoelectric Properties of Permingeatites Cu3Sb1−yGeySe4

Permingeatites Cu3Sb1−yGeySe4 (0 ≤ y ≤ 0.14) were synthesized by mechanical alloying and hot pressing. The charge-transport parameters (Hall coefficient, carrier concentration, mobility, and Lorenz number) and thermoelectric properties (electrical conductivity, Seebeck coefficient, power factor, thermal conductivity, and figure of merit) were examined with respect to the Ge doping level. A single permingeatite phase with a tetragonal structure was obtained without subsequent heat treatment, but a small amount of the secondary phase Cu2GeSe3 was found for the specimens with y ≥ 0.08. All hot-pressed compacts exhibited a relative density of 97.5%–98.3%. The lattice constants of the a-axis and c-axis were decreased by the substitution of Ge at the Sb sites. As the Ge content increased, the carrier concentration increased from 5.2 × 1018 to 1.1 × 1020 cm−3, but the mobility decreased from 92 to 25 cm2·V−1·s−1. The Lorenz number of the undoped Cu3SbSe4 implied a non-degenerate semiconductor behavior, ranging from (1.57–1.56) × 10−8 V2·K−2 at 323–623 K. The thermoelectric figure of merit was 0.39 at 623 K, resulting from a power factor of 0.49 mW·m−1·K−2 and a thermal conductivity of 0.76 W·m−1·K−1. However, the Lorenz numbers of the Gedoped specimens indicated degenerate semiconductor characteristics, increasing to (1.63–1.94) × 10−8 V2·K−2 at 323–623 K. The highest thermoelectric figure of merit of 0.65 was at 623 K for Cu3Sb0.86Ge0.14Se4, resulting from the significantly improved power factor of 0.93 mW·m−1·K−2 and the thermal conductivity of 0.89W·m−1·K−1. As a result, the thermoelectric properties were remarkably enhanced by doping Ge into the Sb sites of the permingeatite.

Assessing the quality of the excess chemical potential flux scheme for degenerate semiconductor device simulation

The van Roosbroeck system models current flows in (non-)degenerate semiconductor devices. Focusing on the stationary model, we compare the excess chemical potential discretization scheme, a flux approximation which is based on a modification of the drift term in the current densities, with another state-of-the-art Scharfetter–Gummel scheme, namely the diffusion-enhanced scheme. Physically, the diffusion-enhanced scheme can be interpreted as a flux approximation which modifies the thermal voltage. As a reference solution we consider an implicitly defined integral flux, using Blakemore statistics. The integral flux refers to the exact solution of a local two point boundary value problem for the continuous current density and can be interpreted as a generalized Scharfetter–Gummel scheme. All numerical discretization schemes can be used within a Voronoi finite volume method to simulate charge transport in (non-)degenerate semiconductor devices. The investigation includes the analysis of Taylor expansions, a derivation of error estimates and a visualization of errors in local flux approximations to extend previous discussions. Additionally, drift-diffusion simulations of a p–i–n device are performed.

Ordered sphalerite derivative Cu5Sn2S7: a degenerate semiconductor with high carrier mobility in the Cu-Sn-S diagram

Regardless the complexity of the phase diagram of the Cu-Sn-S system, several compositions near the prototypical mohite Cu2SnS3 have arisen as potential non-toxic, earth-abundant and cost-efficient photovoltaic and thermoelectric materials....

Enhanced optical and thermoelectric properties of ZnO by tin and fluorine codoping: First-principles DFT calculations

Ab initio density functional calculations of the structural, optoelectronic, thermoelectric and thermodynamic properties of ZnO codoped with tin and fluorine with possible application as Transparent Conductive Oxides (TCO’s), are reported in this work. This study shows that incorporation of Sn and F into the ZnO matrix converts it to a degenerate semiconductor. The calculated optical absorption coefficients show that the four compounds ZnO, Sn:ZnO, F:ZnO and Sn:F:ZnO have transparent properties in the visible range. At 900[Formula: see text]K, the Seebeck coefficient of Sn:F:ZnO is greatly improved with respect to the undoped ZnO. A maximum electrical conductivity value of [Formula: see text]S cm[Formula: see text]s[Formula: see text] is predicted for Sn-doped ZnO. ZT increases with temperature to a maximum value of 0.13 at 900[Formula: see text]K for tin and fluorine codoped ZnO.

(Ba,K)(Zn,Mn)2Sb2: A New Type of Diluted Magnetic Semiconductor

A series of polycrystalline samples of a new diluted magnetic semiconductor (DMS) (Ba,K)(Zn,Mn)2Sb2 has been synthesized and systematically studied. The parent phase is the so-called “Zintl compound” BaZn2Sb2, a week-degenerate semiconductor with a narrow band gap of 0.2 eV. In (Ba,K)(Zn,Mn)2Sb2, the charge is doped by (Ba,K) substitution while the spin is independently doped by (Zn,Mn) substitution. (Ba,K)(Zn,Mn)2Sb2 and analogue (Ba,K)(Zn,Mn)2As2 have comparable narrow band gaps, carrier and spin concentrations. However, the former establishes a short-range spin-glass order at a very low temperature (<10 K), while the latter forms a long-range ferromagnetic ordering with a Curie temperature up to 230 K. The sharp contrast makes (Ba,K)(Zn,Mn)2Sb2 to be a touchstone for DMS theoretical models.