Rectifier With PN Clamp Regions Under Trenches

A structure that includes a rectifier is formed as follows. A trench is formed in a semiconductor region of a first conductivity type. A dielectric layer is formed along opposing sidewalls of the trench but is discontinuous along the bottom of the trench. A doped liner is formed over the dielectric layer and along the bottom of the trench. The doped liner includes dopants of a second conductivity type and is in direct contact with the semiconductor region along the bottom of the trench. A portion of the dopants are diffused from the doped liner into the semiconductor region along the bottom of the trench to form a doped region. The doped region forms a PN junction with the surrounding semiconductor region.