Origin of the Out-of-Equilibrium Body Potential In Silicon on Insulator Devices With Metal Contacts

This work addresses the origin of the transient body potential variation in silicon on insulator (SOI) with deposited metal contacts, under back-gate bias sweep from accumulation to inversion. The phenomenon arises from the difficulty to inject carriers into the silicon film due to the Schottky contact between the metal and the low p-type doped silicon. The Schottky diode current is controlled by the back-gate voltage, which fixes the potential at the bottom of the low-doped film. When the back-gate voltage drives the silicon film towards inversion, the limited current from the Schottky contact induces a deficit of minority carriers in the film and brings the body potential in an out-of-equilibrium regime. This phenomenon will be reproduced with numerical modelling based on Poisson and continuity equations, including the quasi-Fermi potential. The transient character and its dependence on the Schottky barrier height will be evidenced. A simple and effective combination of the classic Schottky current equation and inversion current calculated from the Lambert function, as in fully depleted (FD)-SOI MOSFETs, confirms the origin of the effect.