LOW-DISTORTION ALGAAS INGAAS POWER HFETS WITH QUANTUM-DOPED GRADED-LIKE CHANNELS/

We report on the fabrication and characterization of quantum-doped gra ded-like channel heterojunction field-effect transistors (HFETs) by mo lecular beam epitaxy (MBE) using a multiple pulse doping technique. Th e extended equations describing the piecewise doping profiles have bee n developed to derive the transconductance and second-harmonic to fund amental ratio. It is found that the thickness of depletion width domin ates the maximum transconductance and the high doping gradient offers the device linearity. Two HFETs with different doping gradients have b een fabricated to elucidate this concept. We obtain the maximum extrin sic transconductance of 165 mS mm(-1). Both have broad plateaus on the ir transconductance versus gate-to-source voltage profiles. Further, t he devices exhibit a gate-to-drain and a drain-to-source breakdown vol tage larger than 25 V. The very small output conductance and good pinc h-off characteristics indicate good confinement of the electrons in a quantum-doped channel.