Semiconductor to metal transition in bilayer phosphorene under normal compressive strain

TL;DR

This study demonstrates that applying normal compressive strain to bilayer phosphorene induces a reversible transition from semiconductor to metal at around 13.35% strain, enabling tunable electronic properties without degrading transport characteristics.

Contribution

It reveals a practical method to tune electronic properties of bilayer phosphorene via normal compressive strain, which is easier to implement experimentally compared to previous approaches.

Findings

Semiconductor to metal transition at ~13.35% strain

Direct to indirect bandgap transition at ~3% strain

Structural integrity maintained at high strain levels

Abstract

Phosphorene, a two-dimensional (2D) analog of black phosphorous, has been a subject of immense interest recently, due to its high carrier mobilities and a tunable bandgap. So far, tunability has been predicted to be obtained with very high compressive/tensile in-plane strains, and vertical electric field, which are difficult to achieve experimentally. Here, we show using density functional theory based calculations the possibility of tuning electronic properties by applying normal compressive strain in bilayer phosphorene. A complete and fully reversible semiconductor to metal transition has been observed at $\sim13.35\%$ strain, which can be easily realized experimentally. Furthermore, a direct to indirect bandgap transition has also been observed at $\sim3\%$ strain, which is a signature of unique band-gap modulation pattern in this material. The absence of negative frequencies in phonon spectra as a function of strain demonstrates the structural integrity of the sheets at relatively higher strain range. The carrier mobilities and effective masses also do not change significantly as a function of strain, keeping the transport properties nearly unchanged. This inherent ease of tunability of electronic properties without affecting the excellent transport properties of phosphorene sheets is expected to pave way for further fundamental research leading to phosphorene-based multi-physics devices.