Design, fabrication and characterization of GaN-based HFET's

AlGaN-GaN modulation doped field effect transistors (MODFETs) with short gates show great promise for high power microwave amplifier applications. The lattice mismatch between Al/sub x/Ga/sub 1-x/N limits the thickness and/or the fraction of Al in the barrier. An upper limit of x=0.40 exists for 150 /spl Aring/ thick barriers for example, although lower x values and thicker barriers are commonly used. It is also possible to dope the channel, as well as the barrier. A simple analytical design model has been developed to show the tradeoff of 2DEG density with barrier composition and thickness, channel composition and thickness, and the location and sheet density of atomic planar doping.