The influence of gate-feeder/mesa-edge contacting on sidegatingeffects in In0.52Al0.48As/In0.53Ga0.47As 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 _0.52Al_0.48As/In_0.53Ga_0.47As. 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_ds) current level at sidegate voltages (V_sg) extending up to -30 V, while the non-air-bridge configuration of HFETs show a 30% drop of I_ds at the same V _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