Enhancement-Mode Operation of Nanochannel Array (NCA) AlGaN/GaN HEMTs

In this letter, enhancement-mode (E-mode) AlGaN/ GaN high electron mobility transistors (HEMTs) were demon- strated based on lateral scaling of the 2-D electron gas channel using nanochannel array (NCA) structure. The NCA structure consists of multiple parallel channels with nanoscale width defined by electron-beam lithography and dry etching. Because of the improved gate control from the channel sidewalls and partially relaxed piezoelectric polarization, the fabricated 2 μm-gate-length NCA-HEMT with a nanochannel width of 64 nm showed a thresh- old voltage of +0.6 V and a higher extrinsic transconductance of 123 mS/mm, compared to -1.6 V and 106 mS/mm for the conventional HEMT with μm-scale channel width. The scaling of threshold voltages, peak transconductance, and gate leakage as a function of the nanochannel width were investigated. Small-signal RF performance of NCA-HEMTs were characterized for the first time and compared with those of conventional HEMTs.