Enhancement-mode InAlAs/InGaAs/InP HEMTs with Ir-based gate metallization

The reliability of high electron mobility transistors (HEMTs) significantly depends on the stability of the gate Schottky contact to the semiconductor. Gate sinking during the fabrication and device operation alters transconductance, gate capacitance, and threshold voltage, which are crucial device parameters for modeling HEMT devices and designing circuits. In particular for enhancement-mode InAlAs/InGaAs/InP HEMTs (eHEMTs) where thermally-treated Pt is utilized as the gate metallization, thermal stability has always constituted a problem due to the diffusion of Pt. Although aspects of this diffusion are utilized to enhance e-mode behavior, no quantitative measurements have been conducted to estimate the diffusion depth of Pt in InAlAs. Further, it would be preferable to develop a metallization scheme where the Schottky contact barrier height is similar to that of Pt but with a much lower diffusivity. To this end, we have developed a gate metal structure based on Ir for InAlAs/InGaAs/InP HEMTs and investigated its thermal stability in comparison to the conventional Pt-based contact. A 0.15 um-gatelength eHEMT utilizing Ir/Ti/Pt/Au gate was fabricated to demonstrate the potential of Ir-based gate technology