First-principles theory of field-effect doping in transition-metal dichalcogenides: Structural properties, electronic structure, Hall coefficient, and electrical conductivity

TL;DR

This study uses density-functional theory to analyze how field-effect doping influences the structural, electronic, and transport properties of few-layer transition-metal dichalcogenides, revealing non-rigid band shifts and deviations in Hall measurements.

Contribution

It provides a comprehensive first-principles analysis of doping effects on layered TMDs, including a database of electronic structures and Hall coefficients, highlighting the importance of structural relaxation under electric fields.

Findings

Electronic structure depends on layer number and doping, not just rigid band shifts.

Structural relaxation under electric fields is crucial for accurate modeling.

Hall measurements can significantly deviate from actual doping charges, sometimes with incorrect polarity.

Abstract

We investigate how field-effect doping affects the structural properties, the electronic structure and the Hall coefficient of few-layers transition metal dichalcogenides by using density-functional theory. We consider mono-, bi-, and trilayers of the H polytype of MoS2, MoSe2, MoTe2, WS2, and WSe2 and provide a full database of electronic structures and Hall coefficients for hole and electron doping. We find that, for both electron and hole doping, the electronic structure depends on the number of layers and cannot be described by a rigid band shift. Furthermore, it is important to relax the structure under the asymmetric electric field. Interestingly, while the width of the conducting channel depends on the doping, the number of occupied bands at each given k point is almost uncorrelated with the thickness of the doping-charge distribution. Finally, we calculate within the constant-relaxation-time approximation the electrical conductivity and the inverse Hall coefficient. We demonstrate that in some cases the charge determined by Hall-effect measurements can deviate from the real charge by up to 50%. For hole-doped MoTe2 the Hall charge has even the wrong polarity at low temperature. We provide the mapping between the doping charge and the Hall coefficient. In the appendix we present more than 250 band structures for all doping levels of the transition-metal dichalcogenides considered within this work.