Thermoelectric properties of Si-based materials

Abstract

We studied whether or not Si-based materials, which were prepared by arc melting Si with Ge and a small amount of Group 3B or 5B elements, could be produced with high performance thermoelectric properties. The present materials have not only strong alloy segregation but also strong dopant segregation along the grain boundaries at high carrier concentration n of above 1019 cm"3. The combination of alloying with 5 at%Ge and doping with 0.3 at%B or 0.4 at%P decreased the thermal conductivity K to 5.7% or 6.7% of pure Si at 298 K, respectively, in spite of strong segregation. The electrical resistivities p of doped Si and Si0.97Ge0.o3 decrease linearly with increasing. However the Seebeck coefficient S of doped Si have a local maximum at(3~4) x 1019cm-3, while no S maximum was observed in doped Si0.97Ge0.o3. At = 2xl020cm~3 the S values of Sio.9?Geo.o3 and Sio.gsGeo.os with strong segregation are about 50% higher than those measured previously on Sio.95Ge0.o5 and Si0.7Ge0.3 with little segregation. Such interesting phenomena of S may probably result from the grain boundary segregation of dopants and/or Ge. The thermoelectric figures of merit (ZT=S2T/Kp) of n- and p-type Si0.95Ge0.o5 increase linearly with temperature T, and were 0.90 and 0.57 at 1073 K, respectively. These values correspond to 92% and 81% of those obtained by Dismukes et al. for Sio.7Ge0.3 alloys with little segregation.