Tri-Gate Al_0.2Ga_0.8N/AlN/GaN HEMTs on SiC/Si-Substrates

Abstract

A nanochannel array structure was applied to realize enhancement-mode high electron mobility transistors based on AlGaN/AlN/GaN-heterostructures grown on Si substrates using a SiC transition layer. The fabricated nanochannel array HEMT, consisting of 78 channels connected in parallel with a channel width of 100 nm defined by electron-beam lithography and dry etching, shows a threshold voltage of 0.35 V. The high electron mobility transistors with LG= 0.2 μm had a maximum drain current density of 445 mA/mm and a peak extrinsic tranconductance of 235 mS/mm. A unity current gain cut-off frequency of 30 GHz and maximum oscillation frequency of 40 GHz were measured on these devices.

Enhancement- and depletion-mode AlGaN/GaN HEMTs on 3C-SiC(111)/Si(111) pseudosubstrates

“…Comparison of the cutoff frequencies of our E‐mode tri‐gate and D‐mode planar GaN/Al 0.2 Ga 0.8 N/AlN/GaN HEMTs on Si with our last results and with the best f T data reported by other groups for AlGaN/GaN HEMTs on Si and on SiC .…”

“…Note that f max exceeds f T for the tri‐gate device which is uncommon if rectangular gates are used, but was also observed in Ref. .…”

“…The steeper threshold voltage dependence in comparison to Ref. was achieved by changing the etching conditions to improve the sidewall geometry. The SiN passivation increases the effective barrier thickness and changes the stress state and interface state density.…”

“…A recent realization of E‐mode HEMTs are multi‐mesa‐channel (MMC) structures or nanochannel arrays (NCA). They employ a tri‐gate structure , where the gate is wrapped around narrow AlGaN/GaN bodies from three sides (from the top and from both perpendicular sidewalls), similar to the tri‐gate Si MOSFETs which currently enjoy increasing popularity. Other possibilities to fabricate E‐mode AlGaN/GaN HEMTs are ultrathin AlGaN barriers , gate recess , or fluorine plasma treatment .…”