Strain-engineered p-type to n-type transition in mono-, bi- and tri-layer phosphorene

Using density functional theory, a detailed computational study is performed to explore the structural and electronic properties of a phosphorene monolayer, bilayer and trilayer under a uniaxial strain along the armchair (baxis) and zigzag (a axis) directions. In the case of a monolayer phosphorene, it is found that strain along the armchair direction slightly affects the a lattice parameter and the puckering height (Δ). Along the zigzag direction, however, variation of the a lattice parameter is compensated by both the a and b lattice parameters while the parameter Δ remains unaffected. In terms of electronic properties, strain along the armchair and zigzag directions changes the nature of the Γ point in the bandgap from a direct to an indirect electronic transition as a function of the strain value. In the strain range from -14% to +6%, all phosphorene structures behave like most semiconductors under strain. However, size and strain combined effect significantly affects the Fermi energy position. Around 0% strain, all phosphorene structures are of p-type, while they switch to an n-type semiconductor in the range of strain values from +2% up to +14%. This p-type to n-type transition may have a major technological impact in fields where mono- and hetero-junctions are needed.