Electrical characteristics of Al_xGa_1-xN/GaN heterostructure with isoelectronic Al-doped channel for HFET application

Based on investigating the effects of isoelectronic Al-doping on GaN film, a new layer structure is proposed for a heterostructure field effect transistor (HFET) including an isoelectronic Al-doped channel. The electron mobility measured at 77 (300) K significantly increased from 145 (130) cm²/V·s in the undoped sample to 823 (440) cm²/V·s in the Al-doped sample grown with a trimethylaluminum flow rate of 3 μmol /min, while maintaining the background doping concentration below ∼ 6 × 10¹⁶ cm^-3. Two-dimensional electron gas mobilities of 1690 and 9280 cm²/Vs were measured for a 25-nm Al_0.3Ga_0.7N/1-nm AlN/70-nm Al-doped channel/GaN heterostucture at 300 and 77 K, respectively. The improved results are explained based on a decrease in the compensating acceptors or other defects associated with the formation of screw dislocation due to the incorporation of Al in the channel layer, plus a decrease in the alloy disorder scattering in the heterostructure based on introducing a binary thin A1N layer between the Al_0.3Ga_0.7N and Al-doped channel layers.