Layered (IV-VI)-(V-VI)-materials for low dimensional thermoelectric structures

Abstract

(IV-VI)-(V-VI) nanostructures are new systems, which could be used both for the reduction of thermal conductivity and for MQW structures to enhance electrical conductivity. We report on both first steps: IV-VI on V-VI and V-VI on IV-VI growth in the bismuth telluride/lead telluride material system using molecular beam epitaxy. Bismuth telluride layers were grown using element sources, PbTe and PbSe can be grown using the binary compounds. n-PbTe and n-PbSe as well as n-bismuth telluride layers were grown epitaxially on [111]-barium fluoride-substrates. [111]-barium fluoride is probably the best suited substrate for both IV-VI and V-VI-materials due to its small lattice mismatch. The IV-VI-initial-layers were overgrown with n-bismuth telluride, while the V-VI-initial-layers were overgrown with PbTe or PbSe. We report on growth characteristics analysed by AFM, ECP, SEM and SIMS, depending on various growth conditions like substrate temperature and layer thickness. The results taken from as grown samples and after annealing procedures are discussed with respect to the crystal structures accordingly and the ternary phase diagram of bismuth telluride/lead telluride.