US Patent 7728403 Semiconductor device

A semiconductor device of unipolar type has Schottky-contacts (6) laterally separated by regions in the form of additional layers (7, 7″) of semiconductor material on top of a drift layer (3). Said additional layers being doped according to a conductivity type being opposite to the one of the drift layer. At least one (7″) of the additional layers has a substantially larger lateral extension and thereby larger area of the interface to the drift layer than adjacent such layers (7) for facilitating the building-up of a sufficient voltage between that layer and the drift layer for injecting minority charge carriers into the drift layer upon surge for surge protection.