Title: Impact Ionization in $β-Ga_2O_3$,
Abstract: A theoretical investigation of extremely high field transport in an emerging
wide-bandgap material $\beta-Ga_2O_3$ is reported from first principles. The
signature high-field effect explored here is impact ionization. Interaction
between a valence-band electron and an excited electron is computed from the
matrix elements of a screened Coulomb operator. Maximally localized Wannier
functions (MLWF) are utilized in computing the impact ionization rates. A
full-band Monte Carlo (FBMC) simulation is carried out incorporating the impact
ionization rates, and electron-phonon scattering rates. This work brings out
valuable insights on the impact ionization coefficient (IIC) of electrons in
$\beta-Ga_2O_3$. The isolation of the $\Gamma$ point conduction band minimum by
a significantly high energy from other satellite band pockets play a vital role
in determining ionization co-efficients. IICs are calculated for electric
fields ranging up to 8 MV/cm for different crystal directions. A Chynoweth
fitting of the computed IICs is done to calibrate ionization models in device
simulators.