  In recent years, researchers have manifested their interest in the
two-dimensional (2D) mono-elemental materials of group-VI elements because of
their excellent optoelectronic, photovoltaic and thermoelectric properties.
Despite the intensive recent research efforts, there is still a possibility of
novel 2D allotropes of these elements due to their multivalency nature. Here,
we have predicted a novel 2D allotrope of tellurium (ring-Te) using density
functional theory. Its stability is confirmed by phonon and ab-initio molecular
dynamics simulations. The ring-Te has an indirect band gap of 0.69 eV (1.16 eV)
at PBE (HSE06) level of theories and undergoes an indirect-direct band gap
transition under the tensile strain. The higher carrier mobility of holes
(~103cm$^2$V$^{-1}$s$^{-1}$), good UV-visible light absorption ability and low
exciton binding (~0.35 eV) of ring-Te gives rise to its potential applications
in optoelectronic devices. Further, the electrical contact of ring-Te with
topological Dirac semimetal (sq-Te) under the influence of electric field shows
that the Schottky barriers and contact types can undergo transition from p-type
to n-type Schottky contact and then to ohmic contact at higher electric field.
Our study provides an insight into the physics of designing high-performance
electrical coupled devices composed of 2D semiconductors and topological
semimetals.
