GATE METALLURGY EFFECTS IN INAS ALSB HFETS - PRELIMINARY-RESULTS AND DEMONSTRATION OF SURFACE FERMI-LEVEL SHIFTS/

The effect of gate metallurgy on depletion-mode InAs/AlSb heterostruct ure field-effect transistors (HFETs) is studied for the first time by carefully comparing the characteristics of Al- and Ti/Au-gate transist ors. HFETs fabricated simultaneously from the same molecular beam epit axial layers and processed identically, but differing only in the meta l used for the gate electrode, feature very different gate and drain I -V characteristics. The metal dependence indicates that the Fermi leve l is not completely pinned at the surface of InAs/AlSb quantum wells. We also show that the gate metal modifies the charge control propertie s of InAs/AlSb HFETs: Al-gate HFETs exhibit an enhanced kink effect ac companied by a marked transconductance compression at zero gate bias, whereas the Ti/Au-gate devices exhibit nearly kink-free drain characte ristics. The gate metal dependence is shown to be a consequence of the increased channel equilibrium electron concentration accompanying the Al-metallization.