Correlation of materials characteristics with microwave device performance in AlGaN high electron mobility transistors

AlGaN based high electron mobility transistors offer the promise of 5-10X the power density of similar InP and GaAs based structures coupled with attractive noise figure, at frequencies up to mmWave. Although significant advances in materials deposition and device fabrication have been made, the quality and reproducibility of epitaxial structures deposited on mismatched substrates remains a key factor limiting device performance. We have fabricated AlGaN HEMTs using structures deposited on sapphire and high resistivity SiC substrates in various MOCVD systems with distinct cross wafer uniformity traits. The resulting device DC and small signal RF characteristics show a strong correlation to cross wafer trends measured prior to processing using a range of nondestructive physical and electrical techniques. These provide an approach for rapid and effective characterization of AlGaN HEMT material that can be implemented prior to device processing, and provide predictive information on completed device performance. Projections indicate that devices fabricated from AlGaN MODFETs will provide 610 Watts/mm of output power density (>10X the power density for GaAs and InP based devices), due to their inherent breakdown field strength and transport properties. An additional benefit of the high breakdown voltage is improved efficiency over GaAs at high output power levels, which occurs due to the high output impedance of the wide bandgap material. Although initial development in this materials system was largely focused on optical devices for lighting and data storage, demonstrations of the frequency 1 , noise 2 , and power performance