How to resolve warning "Average variation in charge over contact 'AAA' interfaces exceeds tolerance"



This particular warning is generated in the CHARGE solver when the doping density in the semiconductor surface (in contact with metal contact AAA) has a non-uniform doping. By default, when an electrical contact boundary condition is defined for a metal region in the CHARGE solver, the contact type is set to “ohmic.” This means that the work function of the metal is updated according to the work function of the semiconductor that is in contact with the metal so that the metal-semiconductor interface forms an ohmic contact. Since the work function of the semiconductor depends on the doping density, if the doping density in the semiconductor varies withing the contacted region, the solver cannot set the metal work function of a certain fixed value to match with the semiconductor work function.

The simplest way to resolve this warning message is to adjust the doping profile in the semiconductor so that there is no variation in the doping density within the contacted region. If this doping variation is intentional then the “force ohmic” option in the properties of the electrical contact boundary condition should be disabled so that the solver can calculate the Schottky barrier at the contact.