THE FREE-BOUNDARY PROBLEM OF A SEMICONDUCTOR IN THERMAL-EQUILIBRIUM

The quasi-hydrodynamic model for semiconductor devices in thermal equi librium admits in general solutions for which the electron or hole den sity vanish. These sets are called vacuum sets. In this paper estimate s on the vacuum sets and a first step in the regularity of the free bo undary of these sets are presented. Numerical examples, including erro r estimates for linear finite elements, for the devices diode, bipolar transistor and thyristor indicate that the free boundary is more regu lar than theoretically predicted.