Impact of Si doping on radio frequency dispersion in unpassivated GaN/AlGaN/GaN high-electron-mobility transistors grown by plasma-assisted molecular-beam epitaxy

We report on the effect of Si doping on the transient behavior of unpassivated high-power GaN/AlGaN/GaN high-electron-mobility transistors grown by plasma-assisted molecular-beam epitaxy on 6H-SiC. The incorporation of Si into the heterostructure barrier is found to reduce the level of radio frequency dispersion as compared to undoped structures. In some devices which incorporate Si doping of the barrier, the pulsed and steady-state current-voltage characteristics coincide, and gate lag is found to be insignificant. More typically, similar to90% of the dc value of drain current is restored at 1 mus after pulsing the gate from pinch off to V-GS=0 V. Significant gate lag is observed in devices that are not doped with Si. In the undoped structure, the drain current reaches only similar to70% of the dc value within 1 mus. The transient behavior in the two designs is attributed to the same defect state with activation energy of 0.22 eV. Dispersion reduction is correlated with an increase of gate leakage current in Si-doped devices. (C) 2003 American Institute of Physics.