First principles modelling of tunnel field-effect transistors based on heterojunctions of strained Germanium/InGaAs alloys

It was studied how the band alignment is affected by the disorder, the stoichiometry composition and the diffusion of atoms at the interface. Calculations on the relative interface formation energy were performed to determine the relative stability of the various models for the interface. Results show how the heterojunction type changes when going from As-rich to Ga-rich conditions and with the diffusion of atoms over a few layers.

These results explain the interval range of the experimental measurements and highlight the challenge of obtaining a Ge/GaAs TFET as this implies the control of atomic diffusion at the interface. Results also show that As-rich interface conditions are more favourable than Ga-rich conditions and that the contribution of disorder at the interface to the potential line-up is negligible. Further, preliminary studies were performed for band gaps of strained Ge and InGaAs alloys.

Besides, an alternative approach to the expensive MBPT was developed based on enforcing Koopman’s theorem to DFT to obtain accurate band gaps at a low computational cost.