  Recently fabricated two dimensional (2D) phosphorene crystal structures have
demonstrated great potential in applications of electronics. In this work,
strain effect on the electronic band structure of phosphorene was studied using
first principles methods. It was found that phosphorene can withstand a surface
tension and tensile strain up to 10 N/m and 30%, respectively. The band gap of
phosphorene experiences a direct-indirect-direct transition when axial strain
is applied. A moderate -2% compression in the zigzag direction can trigger this
gap transition. With sufficient expansion (+11.3%) or compression (-10.2%
strains), the gap can be tuned from indirect to direct again. Five strain zones
with distinct electronic band structure were identified and the critical
strains for the zone boundaries were determined. The origin of the gap
transition was revealed and a general mechanism was developed to explain energy
shifts with strain according to the bond nature of near-band-edge electronic
orbitals. Effective masses of carriers in the armchair direction are an order
of magnitude smaller than that of the zigzag axis indicating the armchair
direction is favored for carrier transport. In addition, the effective masses
can be dramatically tuned by strain, in which its sharp jump/drop occurs at the
zone boundaries of the direct-indirect gap transition.
