Role of polarity in SiN on Al/GaN and the pathway to stable contacts

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.

Comparative Study on Schottky Contact Behaviors between Ga- and N-Polar GaN with SiNx Interlayer

“…Secondly, as identified from Figure 3, the Schottky barrier of the LPCVD SiN x /GaN structure is higher than that of the PECVD SiN x /GaN structure. The possible reasons for this are as follows: The deposition temperature of the LPCVD SiN x is above 700 • C, in which case almost all of the NH 3 in the chamber decomposes; thus, very few hydrogen atoms enter into the SiN x [38]. For PECVD, the deposition temperature is below 400 • C. The low deposition temperature results in a high rate of H incorporation in the SiN x .…”

Polarity control and fabrication of lateral polarity structures of III-nitride thin films and devices: progress and prospects

“…Finally, note that SiN x is a highly charge-compensated dielectric, where defect complexes could pin the Fermi level in the upper or lower half of its bandgap. This provides huge opportunities in the band bending modulation of novel N-polar electronic devices [66].…”

(Invited) A Path Toward Vertical GaN Superjunction Devices

“…The phenomenon that allows for the superjunction is the asymmetry in defect incorporation. Specifically, preferential incorporation of shallow donor oxygen occurs in N-polar GaN making it n-type while Ga-polar GaN remains semi-insulating (24,25,(48)(49)(50). In contrast Mg incorporates similarly into GaN for both polarities.…”