  Two-dimensional materials have attracted lots of research interests due to
the fantastic properties that are unique to the bulk counterparts. In this
paper, from the state-of-the-art first-principles, we predicted the stable
structure of monolayer counterpart of the {\gamma}-CuI (Cuprous Iodide), which
is a p-type wide bandgap semiconductor. The monolayer CuI presents
multifunctional superiority in terms of electronic, optical, and thermal
transport properties. Specifically, the ultralow thermal conductivity of 0.116
Wm-1K-1 is predicted for monolayer CuI, which is much lower than {\gamma}-CuI
(0.997 Wm-1K-1) and other typical semiconductors. Moreover, an ultrawide direct
bandgap of 3.57 eV is found in monolayer CuI, which is larger than {\gamma}-CuI
(2.95-3.1 eV), promoting the applications in nano-/optoelectronics with better
optical performance. The ultralow thermal conductivity and direct wide bandgap
of monolayer CuI as reported in this study would promise its potential
applications in transparent and wearable electronics.
