Electronic transport properties of electron- and hole-doped semiconductingC1bHeusler compounds:NiTi1−x

Abstract

The substitutional series of Heusler compounds NiTi 1−x M x Sn ͑where M = Sc, V and 0 Ͻ x Յ 0.2͒ were synthesized and investigated with respect to their electronic structure and transport properties. The results show the possibility to create n-type and p-type thermoelectrics within one Heusler compound. The electronic structure and transport properties were calculated by all-electron ab initio methods and compared to the measurements. Hard x-ray photoelectron spectroscopy was carried out and the results are compared to the calculated electronic structure. Pure NiTiSn exhibits massive "in gap" states containing about 0.1 electrons per cell. The comparison of calculations, x-ray diffraction, and photoemission reveals that Ti atoms swapped into the vacant site are responsible for these states. The carrier concentration and temperature dependence of electrical conductivity, Seebeck coefficient, and thermal conductivity were investigated in the range from 10 to 300 K. The experimentally determined electronic structure and transport measurements agree well with the calculations. The sign of the Seebeck coefficient changes from negative for V to positive for Sc substitution. The high n-type and low p-type power factors are explained by differences in the chemical-disorder scatteringinduced electric resistivity. Major differences appear because p-type doping ͑Sc͒ creates holes in the triply degenerate valence band at ⌫ whereas n-type doping ͑V͒ fills electrons in the single conduction band above the indirect gap at X what is typical for all semiconducting transition-metal-based Heusler compounds with C1 b structure.

Vacancy induced half-metallicity in half-Heusler semiconductors

“…For example, replacement of Ti by other 3d transition elements in semiconducting NiTiSn and CoTiSb results in a new type of dilute magnetic semiconductor with half-metallic properties. [8][9][10][11][12] Particularly, the high Curie temperature (>700 K) and small lattice mismatch in Fesubstituted CoTiSb makes the compound to a serious candidate for applications in magnetoelectronics and spintronics. 10,11 Vacancies are point defects that occur inherently in all crystalline materials, with equilibrium concentrations of up to 0.1%.…”

“…Recently, great interest has focused on the half-Heusler semiconductors with 18 valence electrons, which comprise promising candidates for high-performance thermoelectric materials, [4][5][6][7] halfmetallic dilute magnetic semiconductors, [8][9][10][11][12] and the recently discovered three-dimensional topological insulators. [13][14][15] One important feature of the 18-electron half-Heusler semiconductors is the coexistence of open d shells and a nonmagnetic ground state.…”

Fabrication and characterization of semiconducting half‐Heusler YPtSb thin films

“…The weak temperature dependence of resistivity has also been observed in bulk YPtSb and other half-Heusler semiconductors [16], a trend markedly different from that in the case of conventional semiconductor materials such as Si. [10,[17][18][19] As seen in Fig. 3(a) the resistivity increased from 500 • C deposition temperature to 700 • C, mainly because of the decreasing carrier density with an increase in deposition temperature ( Fig.…”

Tailoring of the electrical and thermal properties using ultra-short period non-symmetric superlattices

“…33 Considering this activation process as a bandgap E g = 2E A in a semiconductor, the calculated values are smaller than the optical bandgap reported by Aliev et al, [36][37][38] and also significantly smaller than what is expected from ab initio theory. 39,40 Our Hall measurements reveal a high charge carrier density with room temperature values shown in Fig. S2 a.…”