High Phonon-Drag Thermoelectric Efficiency of SiC at Low Temperatures

Abstract

Results confirming the high values of Seebeck coefficient phonon-drag component Sph in SiC are discussed and the relevant consequences to the thermoelectric figure-of-merit ZT=T S 2  / are studied. The fact that Sph increases at low temperatures as T 2.4 similarly for low-doped p-6H- SiC, Si and Ge is demonstrated. Materials comparison criterion Sph  / meff, based on heat conductivity, lattice mobility and carrier effective mass is offered and Sph strength proportions 0.1 : 1 : 5 : 10 for Ge, Si, SiC and C (diamond) are proposed. Related to that high T500K phonon- drag domination limit is obtained for SiC. It is shown that the proportionality Sph , yielding ZT , could reverse some concepts accepted in thermoelectric material development. The best-case calculations predict good (>0.1) and excellent (>1) ZT values with steep temperature-dependence T 3…4 for low temperatures 50200K if sufficiently high electrical conductivity  could be ensured. The last condition may be feasible for n-SiC with relatively shallow donor levels but difficult to achieve in the case of p-SiC with relatively deep acceptor levels.