High-Efficiency AlGaN/GaN/Graded-AlGaN/GaN Double-Channel HEMTs for Sub-6G Power Amplifier Applications

In this article, the superior power performance of a double-channel high-electron-mobility transistor (HEMT) operating at a high drain voltage of sub-6 GHz was demonstrated using a heterostructure of Al0.3Ga0.7N/GaN/AlxGa1-xN/GaN, x ranging from 0.3 to 0, top-down double channel with graded barrier HEMT (DCGB-HEMT). In comparison to single channel HEMT (SC-HEMT), DCGB-HEMT exhibits superior direct current (dc) characteristics, including a wider gate voltage swing, a higher saturation current (up to 1307.80 mA/mm), and a higher OFF-state breakdown voltage (up to 165 V). Through TCAD simulation, the breakdown voltage was increased because the graded barrier reduces the peak value of the electric field at the gate's edge on the drain side. Compared to SC-HEMT, DCGB-HEMT's current collapse (CC) decreased from 23.35% to 9.82%. Electrons from the upper channel are more effectively prevented from being captured by acceptors in a buffer induced by Fe-doping by a thicker 3-D electron gas (3DEG) forming between the bottom channel and graded bottom barrier, prevailing over a thinner 2-D electron gas (2DEG). DCGB-HEMT's maximum power-added efficiency (PAE) increased from 56% to 70.4%. DCGB-HEMTs exhibit superior PAE due to their improved gate control, lower leakage, and improved CC at high drain voltage.