SSD Rectifiers

Abstract

In the previous chapter, it was demonstrated that the trade-off between the on-state and reverse recovery power loss can be greatly improved by merging the physics of the P-i-N rectifier and the Schottky rectifier1 to create the MPS rectifier structure illustrated in Fig. 7.1. In this structure, the drift region is designed using the same criteria as used for P-i-N rectifiers in order to support the desired reverse blocking voltage. The device structure contains a Ps-N junction over a portion under the metal contact and a Schottky contact for the remaining portion. During on-state current flow in the MPS rectifier, most of the current flows via Schottky contact with some modulation of the drift region by injection of holes into the drift region. The on-state voltage drop can be less than that of the P-i-N rectifier under these conditions. At the same time, the carrier distribution in the MPS rectifier has a low value at the anode side making the reverse recovery process much superior to that for the P-i-N rectifier. One drawback of the MPS rectifier structure is the larger leakage current when compared with the P-i-N rectifier due to thermionic emission current flow at the Schottky contact. The leakage current can be reduced to acceptable levels by using a relatively large barrier height and the shielding provided by the P-N junction.