OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Microelectronics; Advanced Materials; Space Technology The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: Develop growth system and process for aluminum scandium nitride (AlScN) and aluminum scandium nitride/gallium Nitride (AlScN/GaN) epitaxial structures to enable next generation radio frequency (RF) transistor technology. DESCRIPTION: Next generation radio frequency (RF) devices are necessary for future Air Force radar and communications systems to advance spectral dominance, range, and efficiency beyond state of the art. This requires new RF transistor technology with higher current and lower losses that can be highly scaled and can operate at high temperatures. High electron mobility transistors (HEMTs) based on AlScN/GaN heterostructures have demonstrated great potential to achieving these goals [1]. Compared to current AlGaN/GaN HEMT technology, AlScN/GaN HEMTs have significantly higher charge density in the two-dimensional electron gas (2DEG) channel, due to higher polarization, resulting in larger on-current and improved device scaling for higher frequency operation. AlScN layer with Sc concentration of ~19% can be epitaxially lattice matched to GaN reducing mechanical strain improving reliability and operating temperatures [2]. To develop this technology, a supply of high quality, uniform, wafer scale AlScN and AlScN/GaN structures will be necessary to produce HEMTs. Currently, ScAlN and ScAlN/GaN is produced only at small laboratory volumes by molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD) due to the challenge of efficiently growing high quality epitaxial AlScN layers with Sc concentrations above 18% [2,3]. To achieve the necessary supply of material for development of RF HEMTs based on AlScN/GaN, a suitable process and equipment are essential. MOCVD is the industry standard for GaN but has been challenging to adapt for growth of AlScN due to the low vapor pressure of Sc containing precursors and low incorporation of Sc, which requires novel equipment and process development. The proposed growth system and process should meet the following thresholds: deposition of Al(1-x)Sc(x)N with Sc concentration (x) greater than 18% (x > 0.18) with a thickness greater than 100 nm and sub nm surface roughness (RMS < 5 nm at 25 m2 scale ) at a growth rate greater than 100nm per hour. Deposition of a Al(1-x)Sc(x)N/GaN device heterostructure with x > 0.18, thin Al(1-x)Sc(x)N layer ( < 50nm) with nm scale thickness uniformity, and sub nanometer surface roughness (RMS < 2nm). Demonstrate the formation of a 2DEG at the AlScN/GaN interface with high sheet concentration (> 8x1012 cm-2). Demonstrate growth on 2 or larger substrates. PHASE I: Determine feasibility, establish a plan, and describe the epitaxial growth process, tool features, and issues for controllable deposition of Al(1-x)Sc(x)N with Sc concentration (x) greater than 18% (x > 0.18) with a thickness greater than 100 nm. Provide detail and documentation that demonstrates the accomplishment of a "Phase I-type" effort, including a feasibility study, which should be clearly identified to potential stakeholders, describing the pathway to integrating with Department of the Air Force (DAF) operations, and outlined how the solution could be used by other DoD or Governmental customers. Information on integrating with existing systems and transition and commercialization plans need to be identified. PHASE II: Develop a fully-functional epitaxy process and system capable of producing Al(1-x)Sc(x)N layers with Sc concentration (x) greater than 18% (x > 0.18) with a thickness greater than 100 nm, and sub nm surface roughness (RMS < 5 nm at 25 m2 scale) at a growth rate greater than 100nm per hour on a 2 or larger substrate. Producing a Al(1-x)Sc(x)N/GaN device heterostructure with x > 0.18, thin Al(1-x)Sc(x)N layer ( < 50nm) with nm scale thickness uniformity, and sub nanometer surface roughness (RMS < 2nm). Demonstrate the formation of a (2DEG) at the AlScN/GaN interface with high sheet concentration (> 8x1012 cm-2) on 2 or larger substrates Identification of manufacturing/production issues and or business model modifications required to further improve the process and device performance should be documented. These Phase II awards are intended to provide a path to commercialization, not the final step for the proposed solution. Delivery of a prototype to Air Force of the fully operational system with appropriate control software is required by the end of Phase II for evaluation. PHASE III DUAL USE APPLICATIONS: The performer shall address scale up and manufacturing of the product developed as a prototype in Phase II. AlScn and AlscN/GaN layers with >80% useable area that meet the Phase II requirements should be achieved. The small business may work with suitable industrial partners for transition to military and civilian applications. An epitaxy process and system of this design will enable devices for efficient high power high frequency RF power amplifiers to replace existing technology for radar and communication applications. Direct access with end users and government customers will be provided with opportunities to receive Phase III awards for providing the government additional research, development, or direct procurement of products and services developed in coordination with the program. REFERENCES: 1. A. J. Green, et al. ScAlN/GaN High-Electron-Mobility Transistors With 2.4-A/mm Current Density and 0.67-S/mm Transconductance , IEEE Electron Device Letters 40, 1056 (2019).; A. J. Green, et al. RF Power Performance of Sc(Al,Ga)N/GaN HEMTS at Ka-Band , IEEE Electron Device Letters 41, 1181 (2020). 2. M. Hardy, et al. Scandium Aluminum Nitride as an Emerging Material for High Power Transistors 2018 IEEE MTT-S International Microwave Workshop Seriec on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP), Ann Arbor, MI, USA, 2018, pp. 1-3 3. S. Leone, et al., "Metal-Organic Vapor Deposition of Aluminum Scandium Nitride Physicia Status Solidi RRL 1900535 (2019).; J. Ligi et. al. Metalorganic chemical vapor phase deposition of AlScN/GaN heterostrucutres Journal of Applied Physics 127, 195704 (2020). KEYWORDS: Wide bandgap semiconductor; epitaxial system; aluminum scandium nitride; gallium nitride; high electron mobility transistors; RF power amplifiers
