Strain-modulated Bandgap and Piezo-resistive Effect in Black Phosphorus Field-effect Transistors

TL;DR

This paper demonstrates that applying mechanical strain to black phosphorus can continuously modulate its bandgap and induce a large piezo-resistive effect, enabling new opto-electronic and electromechanical applications.

Contribution

It introduces the first observation of a large piezo-resistive effect in black phosphorus FETs through strain modulation, expanding its potential for flexible electronics.

Findings

Continuous bandgap modulation via strain in black phosphorus

Large piezo-resistive effect observed at room temperature

Black phosphorus-based strain gauges demonstrated

Abstract

Energy bandgap largely determines the optical and electronic properties of a semiconductor. Variable bandgap therefore makes versatile functionality possible in a single material. In layered material black phosphorus, the bandgap can be modulated by the number of layers; as a result, few-layer black phosphorus has discrete bandgap values that are relevant for opto-electronic applications in the spectral range from red, in monolayer, to mid-infrared in the bulk limit. Here, we further demonstrate continuous bandgap modulation by mechanical strain applied through flexible substrates. The strain-modulated bandgap significantly alters the charge transport in black phosphorus at room temperature; we for the first time observe a large piezo-resistive effect in black phosphorus field-effect transistors (FETs). The effect opens up opportunities for future development of electro-mechanical transducers based on black phosphorus, and we demonstrate strain gauges constructed from black phosphorus thin crystals.