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) is 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 Ω·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-μm gate E-HEMT´s. This is therefore one of the promising devices for ultra-high-speed applications