Modeling and limitations of AlGaN/GaN HFETs

Field effect transistors based upon the AlGaN/GaN system often demonstrate current slump and premature saturation of the gain, accompanied by degradation of the RF output power and power-added efficiency. It is shown that source resistance modulation under high current injection conditions can produce premature saturation effects consistent with experimental data. Elimination of the effect will require design modifications that increase the threshold for space-charge effects to become significant.

Field-Effect Transistors based upon the AIGaN/GaN heterostructure are predicted to be capable of producing RF output power on the order of 10–12 W/mm of gate periphery [1] and spot experimental results indicate performance in agreement with the theoretical predictions, with approximately 10 W/mm RF power [2] obtained in C-band and X-band. Power-added efficiency, with good gain, also approaches the theoretical expectations, at least through C-band. However, the RF performance of these devices of Ten experience limitations due to physical effects that prevent the devices from producing predicted performance. In particular, these devices of Ten demonstrate premature saturation and the gain experiences compression at relatively low RF drive, as shown in Fig. 1.