The influence of gate-feeder/mesa-edge contacting on sidegating effects in In/sub 0.52/Al/sub 0.48/ As/In/sub 0.53/Ga/sub 0.47/As heterostructure FET´s

Sidegating effects in InAlAs/InGaAs heterostructure field effect transistors (HFETs) were experimentally investigated. Two different configurations of gate feeder across the mesa edges are compared in In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As. HFETs. HEMTs and heterostructure insulated-gate FETs (HIGFETs) were fabricated, each with different gate-feeder configurations. HFETs with the gate air bridge over the mesa edge can maintain 99% of the drain-source (I/sub ds/) current level at sidegate voltages (V/sub sg/) extending up to -30 V, while the non-air-bridge configuration of HFETs show a 30% drop of I/sub ds/ at the same V /sub sg/. This significant discrepancy of sidegating effect is attributed to depletion region modulation at the mesa edge below the gate feeder. By lifting the gate feeder above the mesa step, sidegating is reduced, which suggests the channel/substrate trap effects are negligibly small. The role of air-bridge structures in determining the sidegating characteristics is discussed.<>