High Power Ternary Nitride Heterrojunction Transistors

We propose to develop high temperature heterojunction transistors for millimeter wave applications based on material deposition technology for growing epitaxial thin films of a unique series of ternary nitride alloys. The final transistor structure will rely on a gallium nitride (GaN) film as the second member of the heterojunction. Ternary nitrides are excellent candidates for service as transistor bases or channels since they offer a wide range of band gaps which are lower than corresponding binary nitrides (GaN, A1N) while being very closely lattice matched, insuring high gain operation. Our proposed efforts will utilize plasma-enhanced metalorganic chemical vapor deposition, a technology we have developed for the growth of stoichiometeric binary nitrides. Deposition of the unique series of nitride alloys will require the substitution of several suitable precursor species in place of triethylgallium, while maintaining a high flow rate of activated nitrogen species. Phase I studies will determine the best growth conditions by systematically varying the substrate temperature and precursor flow ratios in the gas phase, until the process yields excellent quality wide-gap nitride films. These films will be structurally characterized by electron microscopy and x-ray diffractometry. Additional optical and electrical measurements will provide feedback for optimizing the growth. Preliminary MESFET devices will be fabricated and evaluated. In PHase II, emphasis will be placed on optimization of device performance.