In a general aspect, a method can include forming well region of one conductivity type in a semiconductor region of another conductivity type An interface between the well region and the semiconductor region can define a diode junction at a depth below an upper surface of the semiconductor region. The method can further include forming at least one dielectric region in the semiconductor region. A dielectric region of the at least one dielectric region can have an upper surface that is disposed in the well region at a depth in the semiconductor region that is above the depth of the diode junction; and a lower surface that is disposed in the semiconductor region at a depth in the semiconductor region that is the same depth as the diode junction or below the depth of the diode junction.