Highly Si-Doped GaN Regrown by Metal-Organic Vapor-Phase Epitaxy for Ohmic Contact Applied to Quaternary Barrier-Based High-Electron-Mobility Transistors

The quaternary barrier InAlGaN is suitable for GaN high-electron-mobility transistors (HEMT) power microwave applications. High doping of the semiconductor under the drain and source is a known suitable solution to achieve low ohmic contact resistance. However, InAlGaN quaternary alloys require a low thermal budget to avoid indium desorption from the active layer during regrowth and thus deteriorating the barrier. Herein, a selective-area growth technique at 850 degrees C by metal-organic vapor-phase epitaxy (MOVPE) to achieve low contact resistance with respect to temperature constraint is presented. Regrowth temperature and mask geometry are investigated to achieve selectivity and control of the regrowth rate. The use of H-2 as carrier gas decomposes the GaN buffer layer and damages the surface, creating material cluster during regrowth. Growth with N-2 carrier gas shows nonselective epitaxy, as there are deposits on the entire surface of the dielectric mask. Switching from one carrier gas to another depending on the step in the MOVPE reactor helps to control both the morphology and selectivity. The resulting high doping levels of 8 x 10(19) cm(-3) lead to a low contact resistance of 0.26 omega mm.