  Two-dimensional materials with Rashba split bands near the Fermi level are
key to developing upcoming next-generation spintronics. They enable generating,
detecting, and manipulating spin currents without an external magnetic field.
Here, we propose BiAs as a novel layered semiconductor with large Rashba
splitting in bulk and monolayer forms. Using first-principles calculations, we
determined the lowest energy structure of BiAs and its basic electronic
properties. Bulk BiAs has a layered crystal structure with two atoms in a
rhombohedral primitive cell, similar to the parent Bi and As elemental phases.
It is a semiconductor with a narrow and indirect band gap. The spin-orbit
coupling leads to Rashba-Dresselhaus spin splitting and characteristic spin
texture around the L-point in the Brillouin zone of the hexagonal conventional
unit cell, with Rashba energy and Rashba coupling constant for valence
(conduction) band of $E_R$= 137 meV (93 meV) and $\alpha_R$= 6.05 eV\AA~(4.6
eV{\AA}). In monolayer form (i.e., composed of a BiAs bilayer), BiAs has a much
larger and direct band gap at $\Gamma$, with a circular spin texture
characteristic of a pure Rashba effect. The Rashba energy $E_R$= 18 meV and
Rashba coupling constant $\alpha_R$= 1.67 eV{\AA} of monolayer BiAs are quite
large compared to other known 2D materials, and these values are shown to
increase under tensile biaxial strain.
