Mixed-Conduction Hall-Effect Analysis of High-Temperature Intrinsic Carrier Transport in p-Type Te-Doped Sn(Se 1– x Te x ) Polycrystals

Understanding intrinsic high-temperature carrier-transport properties of narrow-gap thermoelectric semiconductors is essential for optimizing their performance; however, conventional single-carrier Hall-effect analysis loses physical validity with increasing temperature due to the simultaneous excitation of electrons and holes in the intrinsic excitation region. Here, we investigate the temperature-dependent carrier-transport properties of p-type Sn(Se1–xTex) bulk polycrystals with x = 0–0.4 using an electron–hole mixed-conduction model. Both SnSe and Sn(Se1–xTex) enter an intrinsic conduction regime above 550 K, where the single-carrier analysis unrealistically overestimates carrier concentrations and consequently underestimates mobility. Mixed-conduction analysis reveals that the electrons contribute substantially from 370 to 450 K and become comparable to holes above 550 K. In the present polycrystalline SnSe, their high-temperature Hall mobility (∼10 cm2/(Vs)) is limited significantly by grain-boundary potential barriers (51 meV) even at 625 K, whereas the in-grain mobility is much higher (32 cm2/(Vs) at 300 K and 23 cm2/(Vs) at 625 K). Te substitution, which has the same formal charge 2+ as that of Se, significantly increases hole concentration by (i) shifting the acceptor level from deep midgap (EA = 0.59 eV from VBM) in SnSe to near the valence band edge (EA = 0.06 eV) in SnSe0.6Te0.4 and (ii) increasing the acceptor density through the enhanced formation of Sn vacancies, thereby suppressing grain-boundary scattering and enabling much higher electrical conductivity. These results demonstrate that mixed-conduction analysis is indispensable for accurately extracting intrinsic carrier-transport parameters in polycrystalline narrow-gap semiconductors and provide guidelines for optimizing thermoelectric performance at high temperatures.