Record-low contact resistance for InAlN/AlN/GaN high electron mobility transistors on Si with non-gold metal

We have demonstrated 0.17-mu m gate-length In0.17Al0.83N/GaN high-electron-mobility transistors (HEMTs) on Si(111) substrates using a non-gold metal stack (Ta/Si/Ti/Al/Ni/Ta) with a record-low ohmic contact resistance (R-c) of 0.36 Omega mm. This contact resistance is comparable to the conventional gold-based (Ti/Al/Ni/Au) ohmic contact resistance (R-c = 0.33 Omega mm). A non-gold ohmic contact exhibited a smooth surface morphology with a root mean square surface roughness of similar to 2.1nm (scan area of 5 x 5 mu m(2)). The HEMTs exhibited a maximum drain current density of 1110mA/mm, a maximum extrinsic transconductance of 353mS/mm, a unity current gain cutoff frequency of 48 GHz, and a maximum oscillation frequency of 66GHz. These devices exhibited a very small (<8%) drain current collapse for the quiescent biases (V-gs0 = -5V, V-ds0 = 10 V) with a pulse width/period of 200 ns/1 ms. These results demonstrate the feasibility of using a non-gold metal stack as a low Rc ohmic contact for the realization of high-frequency operating InAlN/AlN/GaN HEMTs on Si substrates without using recess etching and regrowth processes. (C) 2015 The Japan Society of Applied Physics