DURIP: Molecular Beam Epitaxy Upgrades to Enable Revolutionary Extreme Bandgap Semiconductors
Abstract
Georgia Institute of Technology Dr. W. Alan DoolittleDURIP: Molecular Beam Epitaxy Upgrades to Enable Revolutionary Extreme BandgapSemiconductorsDURIP: Molecular Beam Epitaxy Upgrades to Enable Revolutionary Extreme Bandgap SemiconductorsAbstractSpurred in part by Ga Tech s innovations, a revolution has begun in extreme bandgap semiconductors (EBGS), such as AlN and Al(GaScYIn)N, with bandgaps exceeding ~5 eV. These EBGS offer unprecedented electrical power, temperature, and voltage capability, surpassing the prior stateof the art by 5-50 times, enabling previously impossible DOD missions. Additionally, EBGS facilitate advanced Deep UV (DUV) optics like lasers, detectors, LEDs enabling optical sterilization, and biological warfare neutralization devices. They are also crucial for emerging high-temperature memory, computation, and acoustic devices. However, the newly discovered epitaxial techniques that have enabled Al-based EBG synthesis are not well aligned with unchanged 40+ year old epitaxy technology. Thus, monies are requested to dramatically lower impurity incorporation in EBGs. These impurities are known to be the performance limiting sources preventing further advances. Molecular beam epitaxy (MBE) systems commonly used for III-Nitride epitaxy today are relics of the 1980#s GaAs era and have not been redesigned in at least 40+ years. These tools were designed for use with substrate temperatures rarely exceeding 600 ºCand for materials that readily condensed on cooled cryopanels. But when using these ancient tool designs for III-Nitride epitaxy, the substrate heaters see temperatures exceeding ~900 ºC becoming sources of outgassed carbon/oxygen bearing gasses that are readily attracted by Al, Sc, Be etc# resulting in high impurity incorporation. And gaseous pumping was an afterthought meaning for EBGs, thenitrogen used is not efficiently pumped away. This limits growth rates which limits the background impurity concentration and the practical device thickness. Finally, the effusion cells of today are nearly identical to those found in the 1980#s. New designs are required that limit impurity outgassing and can withstand the frequent shutter cycles of metal modulated epitaxy (MME), the method shown recently to bypass many of the prior EBGS roadblocks and has excited a new era of EBGS exploration. But MME consumes a ~$12,000 effusion cell every 4-6 months, taking ~3 weeks to recover after each failure. Two 1983 #production# MBE systems are targeted for upgrade to provide the throughput needed to deliver multiple DOD project goals. The total renovation costs for two MBE systems is ~1/3that of a single new MBE system yet provides EBGS advantageous capabilities not found in any commercial MBE system. Upgrades targetthe lower impurity generation with the added benefit of increased growth rates and improved reliability and uptime. Three areas of impurity generation are targeted by the requested upgrades: 1) Dramatically lower outgassing from the substrate heater. In collaboration with UHV Design Inc., Dr. Doolittle has engineered a substrate heater capable of greater than 900 ºC with impurity trapping by liquid nitrogen cooled baffles and should offer a 1-2 order of magnitude improvement in substrate heater outgassing. 2) Massively improved (>620%) pumping capability. For the first time, we propose a cryopump that maximizes the theoretical pumping capacity of an MBE system. 3) Increase reliability, cleaner effusion cells. Using a new design developed by Innovative Advanced Materials Inc., a valved effusion cell that eliminates the source of MME effusion cell failure will be implemented. This cell will not only fix reliability issues found when effusion cells are operated beyond their design limits, but will provide impurity trapping of outgassing heater elements, is field rebuildable and has faster flux modulation. Approved for Public Release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 13, 2025
- Source ID
- N000142512118
Entities
People
- W. Alan Doolittle
Organizations
- Georgia Tech Research Corporation
- Office of Naval Research
- United States Navy