(Invited) Novel Implantation Processing and Characterization for Scalable GaN Power Devices

Wednesday, 4 October 2017: 15:45
Chesapeake B (Gaylord National Resort and Convention Center)
M. S. Goorsky (University of California Los Angeles), T. Bai (UCLA), C. Li (University of California, Los Angeles), M. J. Tadjer (U.S. Naval Research Laboratory), K. D. Hobart (Naval Research Laboratory), T. J. Anderson (NRL), J. K. Hite (Naval Research Laboratory, U.S. Naval Research Laboratory), and B. Feigelson (U.S. Naval Research Laboratory)
Novel ion implantation processing has been introduced to enable p-type doping for high performance vertical GaN p-n power devices. Multicycle Rapid Thermal Annealing (MRTA) leads to state-of the-art p-type doping (> 8% dopant ionization); high n-type doping can also be achieved. The implantation process is also compatible with a tapered implanted junction terminal extension approach to achieve effective edge termination necessary to provide breakdown voltages over 90% of the theoretical maximum value at minimal cost and processing complexity.

MRTA, with ambient control (N2 ambient at 200 psi), pulsed annealing up to ~1400 °C, and an appropriate dielectric encapsulant, is utilized to further improve activation efficiency and, ultimately, p-n junction performance through selective ion implantation and processing optimization. Here, the focus is on MRTA activation of Mg+ implantation, with comparison to the potential effectiveness of other p-type dopants, to assess the impact of the crystalline nature of the substrate and to optimize the encapsulant mask, in order to promote the highest dopant activation. This fundamental study of the role of defects in material produced by GaN epitaxial deposition is expected to lead to a pathway to high activation efficiency through a mechanistic understanding of the relationship between processing methods and performance. The critical link between defects and implant activation will be discussed through the use of novel structural materials characterization techniques as well as standard electrical and optical techniques. Electron microscopy defect analysis, determining the role of implanted and annealed defects, and providing localized strain measurements helps assess defect evolution as a function of implant and annealing parameters. X-ray based reciprocal space mapping as a function of the implant and subsequent annealing will be shown to correlate strain and defect formation with dopant activation in order to parameterize the MRTA process non-destructively. This information leads to the production of p-n junction devices that are scalable, provide high surge currents, and high ideality factors. Understanding point defect concentrations, dislocation types and concentrations, and residual stress will lead to effective p-type dopant activation and high device performance.