Probing the Fermi energy level and the density of states distribution in PbTe nanocrystal (quantum dot) solids by temperature-dependent thermopower measurements.

Abstract

The position of the Fermi energy level (E(F)) with respect to the energy level where the transport process occurs (transport energy level, E(T)) is an important parameter that determines the electrical properties of semiconductors. However, little attention has been devoted to investigating the position of E(F) in semiconductor nanocrystal solids, both theoretically and experimentally. In this study, we perform temperature-dependent thermopower measurements on PbTe nanocrystal solids to directly probe E(F) - E(T). We observe that as the size of the nanocrystals reduces, E(F) - E(T) increases primarily due to the widening of density of state (DOS) gap. Furthermore, by modifying the monodispersity of nanocrystals, we observe an increase in thermopower as the distribution of energy states sharpens. This work promotes a deeper understanding of thermal occupation of energy states as well as electronic transport processes in semiconductor nanocrystal solid systems.