Role of polarity in SiN on Al/GaN and the pathway to stable contacts. (25th March 2020) - Reddy, Pramod
Abstract: Despite being the most widely used dielectric for passivation of GaN-based lateral devices, amorphous silicon-nitride still faces many stability challenges, which arise from its complex bulk electronic and interface properties on the polar (Al)GaN surfaces. In this investigation, SiN has been applied as an ultra-thin interlayer (∼3–5 nm) in vertical contact structures on Ga-polar and N-polar GaN templates to study the metal–insulator–semiconductor- (MIS-) like system and better understand the interaction between the polar surface and its dielectric overlayer. We describe the role of amphoteric ≡Si centers in SiN in passivating and providing the polarization countercharge to Al/GaN of different polarities. The consequent requirements of the concentration profile of the amphoteric defects and the corresponding chemical profile of SiN is discussed. The importance of SiN surface termination and their influence on the interface potential on Al/GaN that determines device performance and reliability is also shown. Finally, a pathway to highly stable and reliable ohmic contacts to n-type Ga-polar GaN without instabilities associated with metal directly alloying with GaN as in the case of traditional contacts is proposed.