Vertical Laser Lifted Off Ultrawide Bandgap AlxGa1-xN Power Electronic Devices Transferred from Bulk AlN for Resilient Adaptable Power Electronics
Abstract
Ultrawide bandgap (UWBG) AlGaN will enable high voltage, high current, reliable, radiation hard devices needed to achieve mid-term high power conversion objectives for DoD applications. A recent 5-year plan for Power Electronic Power Distribution Systems (PEPDS) calls for integrated power electronic building blocks (iPEBB) that seek to increase power handling, requiring a co-design approach that accounts for both electrical and thermal constraints. DoD’s investment in UWBG is predicated on their high critical electrical field (greater than11 MV-cm as measured by our team) approximate 30x that of Si and approximate 3x WBG semiconductors (SiC and GaN), to enable efficient power management in a smaller footprint as codified in the figure of merit (FOM), which predicts greater than9x improvement in power handling for lateral devices, and greater than100x in optimized vertical devices.In this effort, we propose to develop highly miniaturized UWBG iPEBBs using vertical AlGaN transistors, leveraging UofSC co-PI Khan’s proven track record of pioneering WBG AlGaN-GaN lateral transistors. The seed capability for this work includes scaling to UWBG transistors, including a record 1.3A-mm in UWBG AlGaN channels in 2020, a 2022 report that showed 10kA-cm2 in vertical AlGaN diodes, and a 2023 report of record power handling 2GW-cm2 on bulk AlN substrates. Increased power density is required to miniaturize ship power systems, while increasing power switching speed for battlefield agility and to ensure future design of power systems, particularly those using pulse-width modulation (PWM).Due to their intrinsic superior thermal performance (e.g. AlN), compact UWBG iPEBBs allow for much smaller overall footprints over even SiC, or GaN WBG devices, leading to knock-on effects in overall system power usage and efficiency, and system adaptability. However, the full promise of these novel materials has been bottlenecked by the following key issues that we will solve-i) Thermal and electrical resistances of the insulating growth substrates e.g. sapphire-AlN. UWBG devices have very short channels capable of accommodating high voltages. However, the active device electrical resistance becomes so small that the substrate resistance dominates the resistive heat source, giving little advantage over SiC-GaN. To overcome this, we will remove the substrate and transfer the active device with integrated heat spreader to copper heat sinks using a laser liftoff (LLO) technique developed by our team in 2021 that showed a significant thermal advantage.ii) Misfit threading dislocations approximate108cm-2 due to growth on non-native sapphire leading to off-state leakage, limiting the off-state performance of the iPEBB. By growing on bulk AlN substrates, with dislocations approximate104cm-2, defect free devices will be demonstrated. The team has unique access to these substrates not easily available commercially. Moreover, the team’s LLO capability developed on sapphire is applicable to AlN substrates.iii) Doping of UWBG materials for effective electrical contacts to minimize are a challenge we will overcome using pulsed atomic layer epitaxy (PALE), another technique pioneered by mentor co-PI Khan. Recent results on AlN suggest that high doping both p and n-types throughout the AlGaN alloy system is possible.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 06, 2024
- Source ID
- FA95502310506
Entities
People
- M. V. S. Chandrashekhar
Organizations
- Air Force Office of Scientific Research
- Office of the Secretary of Defense
- University of South Carolina