Threshold Voltage Control in Al0.72Ga0.28N/AlN/GaN HEMTs by Work-Function Engineering
نویسندگان
چکیده
The first demonstration of high-Al-composition (> 70%) AlGaN high electron mobility transistors (HEMTs) is reported. High electron mobility (∼1300 cm/Vs at room temperature) was achieved in novel high-Al-composition AlGaN 2-D electron gas structures. The threshold voltages (Vth) of Al0.72Ga0.28N/AlN/GaN HEMTs were shifted from −1.0 to −0.13 V by employing different gate metal stacks, Al/Au and Ni/Au, respectively. With a 4-nm Al2O3 gate dielectric on top of the nitride heterostructures, the ∼0.9-eV work-function difference between Al and Ni induced ∼0.9-V Vth shift in the pairs of the Al/Au and Ni/Au gate HEMTs, which indicates that the Fermi level is unpinned at the ALD Al2O3/AlGaN interface. The results were reproducible for HEMTs of various gate lengths. The results suggest that it is possible to obtain enhancementand depletionmode AlGaN HEMTs using work-function engineering which can enable integrated monolithic digital circuits without postgrowth recess etching or ion implantation.
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