  Triphosphides, with a chemical formula of XP$_3$ (X is a group IIIA, IVA, or
VA element), have recently attracted much attention due to their great
potential in several applications. Here, using density functional theory
calculations, we describe for the first time the structural and electronic
properties of the bulk bismuth triphosphide (BiP$_3$). Phonon spectra and
molecular dynamics simulations confirm that the 3D crystal of BiP$_3$ is a
metal thermodynamically stable with no bandgap. Unlike the bulk, the mono-,
bi-, tri-, and tetra-layers of BiP$_3$ are semiconductors with a bandgap
ranging from 1.4 to 0.06 eV. However, stackings with more than five layers
exhibit metallic behavior equal to the bulk. The results show that quantum
confinement is a powerful tool for tuning the electronic properties of BiP$_3$
triphosphide, making it suitable for technological applications. Building on
this, the electronic properties of van der Waals heterostructure constructed by
graphene (G) and the BiP$_3$ monolayer (m-BiP$_3$) were investigated. Our
results show that the Dirac cone in graphene remains intact in this
heterostructure. At the equilibrium interlayer distance, the G/m-BiP$_3$ forms
an n-type contact with a Schottky barrier height of 0.5 eV. It is worth noting
that the SHB in the G/m-BiP$_3$ heterostructure can be adjusted by changing the
interlayer distance or applying a transverse electric field. Thus, we show that
few-layers BiP$_3$ is an interesting material for realizing nanoelectronic and
optoelectronic devices and is an excellent option for designing Schottky
nanoelectronic devices.
