Edge State and Intrinsic Hole Doping in Bilayer Phosphorene

TL;DR

This study uses a simple LCAO model to analyze edge states in bilayer phosphorene, revealing their role in intrinsic hole doping and effects of electric fields, which could influence device applications.

Contribution

It provides a qualitative analysis of edge states in bilayer phosphorene and explains intrinsic hole doping mechanisms using a simple Harrison LCAO model.

Findings

Edge states in bilayer phosphorene are buried in the valence band.

Buried edge states act as acceptors, causing hole doping.

Vertical electric fields reduce intrinsic hole doping by shifting edge states.

Abstract

Using a simple LCAO model by Harrison, we have qualitatively studied the edge state of bilayer phosphorene, which is a unit structure of the layered crystal of black phosphorus. This model successfully reproduces the isolated edge state in the bulk gap in monolayer phosphorene. In bilayer phosphorene, however, it shows that edge states are almost buried in the valence band and there is no isolated midgap edge state at the zigzag edge. Since the buried edge state works as acceptor, holes are doped from the edge state into the bulk. This gives a possible explanation for p-type conduction in undoped black phosphorus. Under the vertical electric field, the intrinsic hole doping is reduced because a part of edge states move into the gap. These features of bilayer phosphorene might be better suited for device application.