Implementation of the GaN lateral polarity junction in a MESFET utilizing polar doping selectivity

Abstract

The difference in surface energies between the Ga-polar orientation and the N-polar orientation of GaN translates into a completely different behavior for the incorporation of intentional and unintentional impurities. Oxygen is found to be an impurity with higher concentration in the N-polar films than in Ga-polar films and is the cause of n-type conductivity observed in N-polar films. Utilizing this doping selectivity we fabricated a depletion-mode metal-semiconductor field effect transistor (MESFET) with n-type N-polar domains as source and drain and a Ga-polar channel on polarity-patterned wafers. The difference in the electronic properties of the different domains, i.e., as-grown N-polar domains are n-type conductive and Ga-polar domains are insulating, allows for laterally selective doped areas that can be realized for improving contact resistance to the n-type conduction channel. Basically, the N-polar domains acted as the ohmic contacts to the channel localized in a Ga-polar domain. A MESFET with a Schottky gate was fabricated as an example of implementation of this novel structure showing a lowering in the specific contact resistivity.