Improved device linearity of AlGaAs/InGaAs HFETs by a second mesa etching

Conventional mesa isolation process in AlGaAs/InGaAs heterostructure FETs results in the gate contacting the exposed highly doped region at the mesa sidewalls, forming a parasitic gate leakage path. In this letter, we suppress the gate leakage from the mesa-sidewall and enhance microwave power performance by performing additional second mesa etching. The device gate leakage characteristics under high-input power swing are particularly investigated to reveal the improvement of device linearity, which is sensitive to the sidewall gate leakage. This modified device (M-HFETs) provides not only a higher linear rf output power but also a lower IM3 product than those characteristics in conventional HFETs.