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 demonstrated 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
$\mu\hbox{m}$
-gate-length NCA-HEMT with a nanochannel width of 64 nm showed a threshold 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
$\mu \hbox{m}$
-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.