  We systematically investigated the phonon and electron transport properties
of monolayer InSe and its Janus derivatives including monolayer In2SSe and
In2SeTe by first-principles calculations. The breaking of mirror symmetry
produce a distinguishable A1 peak in the Raman spectra of monolayer In2SSe and
In2SeTe. The room-temperature thermal conductivity (\k{appa}) of monolayer
InSe, In2SSe and In2SeTe is 44.6, 46.9, and 29.9 W/(m K), respectively. There
is a competition effect between atomic mass, phonon group velocity and phonon
lifetime. The \k{appa} can be further effectively modulated by sample size for
the purpose of thermoelectric applications. Meanwhile, monolayer In2SeTe
exhibits a direct band and higher electron mobility than that of monolayer
InSe, due to the smaller electron effective mass caused by tensile strain on
the Se side. These results indicate that 2D Janus group-III chalcogenides can
provide a platform to design the new electronic, optoelectronic and
thermoelectric devices.
