High-Quality, Low- Cost Bulk Substrates

An Attempt to Develop the Electrochemical Solution Growth Process Electrochemical Solution Growth Reactor schematic (left) and image (right). Photos courtesy of SunEdison The ever-growing demand in the past decade for more energy efficient solid- suited for scalability to large-area Applications in Our Nation’s state lighting and electrical power manufacturing. The process operated at Industry conversion is leading to a higher demand a low temperature and at atmospheric ESG appeared to be well suited for for wide bandgap semiconductor-based pressure, and was hypothesized to be semiconductor manufacturing in existing devices, such as gallium nitride (GaN), scalable and low cost while providing a six to eight inch (150–200 millimeter) over traditional (Si)-based high growth rate capable of producing silicon (Si) wafer fabrication plants. If devices. High cost and limited large-area, high-quality GaN wafers. it had been successful, GaN substrates availability, however, have hindered the Although project objectives were not produced from the ESG method could adoption of GaN substrates to date. met, bulk GaN continues to be important have been utilized in applications such to bolstering U.S. competitiveness in as optoelectronic devices for , When utilizing GaN, current LED and high-efficiency power and solid-state lighting, high-voltage power power electronic device applications solid-state lighting. employ GaN epitaxially grown on top of electronics, high-performance backlights non-GaN substrates. The lattice mismatch for displays, ultraviolet light-emitting between the epitaxial GaN layer and Benefits for Our Industry and diodes (LEDs), ultraviolet detectors, high the non-native substrate surface leads Our Nation power switching devices, and quantum to considerable stress and high defect It was estimated that successful scaling cascade lasers. densities, ultimately compromising of the ESG growth method to large area device yield and performance. While GaN crystals could reduce the production Project Description bulk growth of GaN can combat these cost of bulk GaN wafers by up to a factor This project attempted to develop ESG issues, current growth methods for of 10. These substrates would have into a viable bulk growth process for bulk GaN have not fostered widespread allowed U.S. manufacturers to cultivate GaN that was scalable to large-area adoption to date due to limited scalability, emerging clean energy technology wafer manufacturing and able to produce low material quality, high operating markets in solid-state lighting and power cost-effective, high-quality bulk GaN temperatures and pressures, and slow electronics, including applications in substrates compared to the current state growth rates. A fundamentally different energy-efficient motors used in large- of the art. The first phase of the project manufacturing route for bulk growth of scale industrial processes and appliances, was designed to refine the laboratory- GaN not driven by thermal processes electric vehicles, and renewable power scale processes, develop a better is needed to provide an adequate generation and integration onto the understanding of molten salt electrolyte value proposition such as a desirable electric grid. Better-performing and reaction kinetics, and develop crystal combination of growth rate, scalability lower-cost GaN substrates can accelerate growth enabling computational flow to larger wafer sizes, electronic-grade the adoption of energy-efficient models. The goal of the second phase was material quality, and manufacturing costs. GaN-based lighting and high-voltage to establish a pilot-scale electrochemical power switching devices, ignite new The objective of this project was to reactor capable of growing wafers six market applications, and reduce U.S. develop Electrochemical Solution inches and larger. power consumption. Growth (ESG) into a viable bulk GaN growth process that would be well

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Barriers of impurities, particularly , Technology Transition • Existing heteroepitaxial growth inhibited the demonstration of crystalline The barriers to thick, high quality GaN techniques of large area GaN on GaN film growth on the seed template. growth on a seed prevent a meaningful , , or Si However, the presence of both Ga transition of the technology toward substrates result in high defect and N at the growth surface indicated commercialization. No benefits compared densities (i.e. wafer bowing and that the reactor hardware physics was to existing GaN growth technologies GaN film cracking) and poor device functioning properly, suggesting that were reported. yield and performance (i.e. higher achieving film growth was a matter leakage currents and lower breakdown of controlling the chemistry at the The final report for the project is voltages). interface. Researchers tried to eliminate available at: https://www.osti.gov/scitech/ the oxygen contamination interference, servlets/purl/1375013 • Traditional semiconductor bulk but they were unable to meet their goal crystal growth techniques are not of depositing 0.5μm of crystalline GaN transferrable to GaN due to its unusual on the GaN seed. The project was put Project Partners thermodynamic properties. on hold while researchers and DOE SunEdison, Inc.* discussed redirecting the project, but in St. Peters, MO • Homoepitaxial approaches (i.e. GaN the interim, SunEdison was acquired by a Principal Investigator (PI): Mike Seacrist films grown on GaN substrates) are not foreign company which initiated a project Email: [email protected] pursuable due to lack of native GaN closeout procedure. substrates. Sandia National Laboratories Albuquerque, NM Milestones Pathways Co-PI: Karen Waldrip This project began in September 2012 but All of the individual components of the was officially terminated in January 2017 Georgia Institute of Technology process were previously demonstrated upon the acquisition of SunEdison by a Atlanta, GA at the laboratory scale. The focus foreign company. Co-PI: Russell Dupuis of the first phase was development of the rotating seed growth process, • Reproducible films of GaN over For additional information, including optimizing and configuring large areas using ESG achieved with the electrolyte chemistry and electrode densities matching the seed please contact type, and configuration for enhanced template (Unmet). Brian Valentine production; conducting extensive Technology Manager modeling to understand ion mobility; • GaN reproducibly produced by ESG on U.S. Department of Energy and developing flow models to optimize two inch (50mm) diameter substrates Advanced Manufacturing Office ion transport to the growth surface and used to epitaxially grow GaN films Phone: (202) 586-9741 of the GaN seed. The second stage to compare with epitaxial GaN grown Email: [email protected]  involved scaling up to a larger reactor on other substrates (Unmet). and producing high-quality crystal for * Formerly known as MEMC • Functional ESG GaN-based power and extensive materials characterization and Electronic Materials, Inc. Sun Edison optical devices from two inch (50mm) prototype device development. Semiconductor is a wholly owned diameter substrates fabricated and subsidiary of GlobalWafers. Phase one’s key objective of the growth tested. Commercial prototype ESG of a crystalline GaN film on the seed reactor manufactured and tested for template was not achieved. The presence growth diameter scalability beyond four inch (100 mm) (Unmet).

For more information, visit: energy.gov/eere/amo

DOE/EE-1688 • December 2017