High-performance 0.1-μm gate enhancement-mode InAlAs InGaAs HEMT's using two-step recessed gate technology

Novel approach for making high-performance enhancement-mode InAlAs/InGaAs HEMT's (E-HEMT's) are described for the first time. Most important issue for the fabrication of E-HEMT's is the suppression of the parasitic resistance due to side-etching around the gate periphery during gate recess etching. Two-step recessed gate technology is utilized for this purpose. The first step of the gate recess etching removes cap layers wet-chemically down to an InP recess-stopping layer and the second step removes only the recess-stopping layer by Ar plasma etching. The parasitic component for source resistance is successfully reduced to less than 0.35 Omega-mm. Etching selectivities for both steps are sufficient not to degrade uniformity of devices on the wafer. The resulting structure achieves a positive threshold voltage of 49.0 mV with high transconductance. Due to the etching selectivity, the standard deviation of the threshold voltage is as small as 13.3 mV on a 3-in wafer. A cutoff frequency of 208 GHz is obtained for the 0.1-mu m gate E-HEMT's. This is therefore one of the promising devices for ultra-high-speed applications.