Thermoelectric properties of epitaxial PbSrTe and PbSrSe bulk and MQW thin films

Experimental evidence for an enhancement of the thermoelectric figure of merit ZT in 2D PbTe/Pb/sub 1-x/Eu/sub x/Te multiple-quantum-well (MQW)-structures was recently reported by Harman et al. (1997). To verify these basic concepts MQW-structures based on the Sr-ternary lead chalcogenides Pb/sub 1-x/Sr/sub x/Se and Pb/sub 1-x/Sr/sub x/Te were investigated. PbSe/Pb/sub 1-x/Sr/sub x/Se MQW have been successfully used for lead salt laser diodes. We present properties of bulk Pb/sub 1-x/Sr/sub x/Se and Pb/sub 1-x/Sr/sub x/Te epitaxial films grown by MBE on freshly cleaved BaF/sub 2/(111). N-type films with carrier concentrations between 10/sup 18/ and 10/sup 20/ cm/sup -3/ can be easily obtained by doping with pure bismuth. XRD and AFM measurements show a high structural quality of these films. The surface roughness of PbSrTe is even less than that of PbTe. Temperature dependent measurements of electrical conductivity and thermopower are reported. The thermoelectrical data of bulk PbTe-films agree well with values given by Harman. For MQW-films XRD and AFM analysis indicate high structural perfection. Measurements of transport properties of PbTe/Pb/sub 1-x/Sr/sub x/Te- and PbSe/Pb/sub 1-x/Sr/sub x/Se-MQW structures were evaluated according to Harman and alternatively with stacked well and barrier layers connected in parallel. Both evaluation methods were performed on different types of MQW structures and doping profiles and yield an enhancement in the power factor for a well thickness less than 3 nm. Additionally first thermal conductivity data on IV-VI MQW structures are presented.