The Need

The potential of different materials for vertical power switching is often assessed by calculating the Baliga Figure of Merit (BFOM). In the case of wide and ultra-wide bandgap materials, the high breakdown fields and the relatively good transport properties make the BFOM significantly higher than conventional Si electronics. However, the breakdown field predicted for a material requires that the entire bandgap be presented across the rectifying junction, such as in a PN junction. This is challenging to achieve in several wide bandgap materials where bipolar doping is not available or presents technological challenges. Schottky junctions can provide excellent rectification but the reverse breakdown of Schottky rectifiers is limited by the Schottky barrier height, which is significantly lower than the bandgap in most wide bandgap semiconductors. Thus, there is a need for an approach that can enable field management so that high breakdown fields can be achieved even in unipolar junctions.

The Technology

A team of researchers at The Ohio State University led by Dr. Siddharth Rajan has developed a method of dielectric heterojunction engineering comprising of a lightly doped n-type or p-type semiconductor drift layer and a high-k material with a dielectric constant that is at least 2 times higher than the value of the semiconductor drift layer. Metal Schottky contact is formed on the high-k material and metal Ohmic contact is formed on the lightly doped semiconductor. Under reversed bias, the dielectric constant discontinuity leads to a very low electric field in the low-k semiconductor drift layer. The electron barrier created by high-k material stays almost flat. Therefore, the dielectric heterojunction maintains a barrier to electron or hole tunneling at much higher voltages than the metal/semiconductor junction. Under forward bias, electrons flow from the semiconductor, through the high dielectric constant layer, into the metal. For small values of conduction band offset or valence band offset between the high-k and low-k material, dielectric heterojunction is expected to support efficient electron or hole transport.

Commercialization

• Photodetectors
• Power electronics

Benefits

• High k dielectric junction enables high breakdown field (5.7 MV/cm)
• Higher reliability
• Lower on-resistance for power electronics