Vertical GaN Power Electronics – Opportunities and Challenges

Tremendous progress has been made in wide-bandgap (WBG) power electronic devices. Most WBG
devices today are based on silicon carbide (SiC) or gallium nitride (GaN). However, the most mature
GaN-based power device, the high electron mobility transistor (HEMT), falls short of the full potential of
GaN for several reasons: (1) internal stress due to the growth of thick buffer layers on non-native
substrates; (2) the lateral architecture of the HEMT produces a non-ideal internal electric field
distribution; and (3) avalanche ruggedness is lacking. GaN-based HEMTs are thus unacceptable for
higher-voltage applications such as the electric grid and vehicle drivetrain electrification. In contrast to
GaN HEMTs, vertical GaN power devices grown on native GaN substrates do not suffer from these
shortcomings. However, materials challenges exist for vertical GaN, such as the quality of native
substrates and the epitaxial growth of thick (tens of microns or more), low-doped (< 10 16 cm -3 n-type)
drift layers required for high breakdown voltage. Processing challenges also exist, such as the ability to
selectively dope GaN and to activate buried p-layers. This talk will present progress in the design,
fabrication, and evaluation of vertical GaN power devices. The fundamental material properties relevant
for such devices will be discussed, including how they enable devices superior to those fabricated from
other semiconductors. Challenges and progress associated with substrates and epitaxial growth will be
covered, as will design trade-offs and processing challenges (including yield and reliability) for various
types of diodes and transistors.