Strain-tunable charge carrier mobility of atomically thin phosphorus allotropes

TL;DR

This study investigates how uniaxial strain influences charge carrier mobility and bandgap properties of atomically thin phosphorus allotropes, revealing significant mobility enhancements and electronic conduction direction changes.

Contribution

It provides the first detailed analysis of strain effects on mobility and bandgap transitions in all four known monolayer phosphorus allotropes using density functional theory.

Findings

Charge mobility increases by 5-10 times under strain.

Strain induces direct-indirect bandgap transitions and bandgap closure.

Significant mobility enhancement (up to 250 times for holes) observed in specific allotropes.

Abstract

We explore the impact of strain on charge carrier mobility of monolayer $\alpha$, $\beta$, $\gamma$ and $\delta$-P, the four well known atomically thin allotropes of phosphorus, using density functional theory. Owing to the highly anisotropic band dispersion, the charge carrier mobility of the pristine allotropes is significantly higher (more than 5 times in some cases) in one of the principal directions (zigzag or armchair) as compared to the other. Uniaxial strain (upto 6% compressive/tensile) leads to bandgap alteration in each of the allotropes, especially a direct to indirect bandgap semiconductor transition in $\gamma$-P and a complete closure of the bandgap in $\gamma$ and $\delta$-P. We find that the charge carrier mobility is enhanced typically by a factor of $\approx 5-10$ in all the allotropes due to uniaxial strain; notably among them a $\approx 250$ (30) times increase of the hole (electron) mobility along the armchair (zigzag) direction is observed in $\beta$-P ($\gamma$-P) under a compressive strain, acting in the armchair direction. Interestingly, the preferred electronic conduction direction can also be changed in case of $\alpha$ and $\gamma$-P, by applying strain.