  Magnesium Selenide (MgSe) is a wide bandgap semiconductor with applications
in optoelectronics and energy conversion technologies. Understanding thermal
conductivity (k) of MgSe is critical for optimum design of thermal transport in
these applications. In this work, we report the temperature and length
dependence lattice thermal conductivity of magnesium selenide (MgSe) with
different crystallographic phases; zincblende, rocksalt, wurtzite and nickel
arsenic, using first principles computations. Computations reveal significant
differences in thermal conductivity (k) of MgSe for different phases. The
observed trend in thermal conductivities is : kNiAs < krocksalt < kwurtzite <
kzincblende. Our first principles calculations show a room temperature low k of
4.5 Wm-1K-1 for the NiAs phase and a high k of 20.4 W/mK for wurtzite phase.
These differences are explained in terms of a phonon band gap in the
vibrational spectra of zincblende and wurtzite phases, which suppresses
scattering of acoustic phonons, leading to high phonon lifetimes.
