P-i-N Rectifiers

Abstract

It was demonstrated in the previous chapters that the on-state voltage drop of silicon Schottky barrier rectifiers becomes large when the device is designed to support more than 200 volts in the reverse blocking mode. Power device applications, such as motor control, require rectifiers with blocking voltages ranging from 300 volts to 5000 volts. Silicon P-i-N rectifiers have been developed for these high voltage applications. In a P-i-N rectifier, the reverse blocking voltage is supported across a depletion region formed with a P-N junction structure. The voltage is primarily supported within the n-type drift region with the properties of the p-type region optimized for good on-state current flow. Any given reverse blocking voltage can be supported across a thinner drift region by utilizing the punch-through design1. Since it is beneficial to use a low doping concentration for the n-type drift region in this design, it is referred to as an i-region (implying that the drift region is intrinsic in nature). The silicon P-i-N rectifiers that are designed to support large voltages rely upon the high level injection of minority carriers into the drift region. This phenomenon greatly reduces the resistance of the thick, very lightly doped drift region necessary to support high voltages in silicon. Consequently, the on-state current flow is not constrained by the low doping concentration in the drift region. A reduction of the thickness of the drift region, by utilizing the punch-through design, is beneficial for decreasing the on-state voltage drop.