  The pursuit to operate photocathodes at high accelerating gradients to
increase brightness of electron beams is gaining interests within the
accelerator community. Cesium telluride (Cs2Te) is a widely used photocathode
material and it is presumed to offer resilience to higher gradients because of
its wider band gap compared to other semiconductors. Despite its advantages,
crucial material properties of Cs2Te remain largely unknown both in theory and
experiments. In this study, we employ first-principles calculations to provide
detailed structural, elastic, electronic and transport properties of Cs2Te. It
is found that Cs2Te has an intrinsic mobility of 20 cm2/Vs for electrons and
2.0 cm2/Vs for holes at room temperature. The low mobility is primarily limited
by the strong polar optical phonon scattering. Cs2Te also exhibits ultralow
lattice thermal conductivity of 0.2 W/(m*K) at room temperature. Based on the
energy gain/loss balance under external field and electron-phonon scattering,
we predict that Cs2Te has a dielectric breakdown field in the range from ~60
MV/m to ~132 MV/m at room temperature dependent on the doping level of Cs2Te.
Our results are crucial to advance the understanding of applicability of Cs2Te
photocathodes for high-gradient operation.
