Modulation-Doped Field Effect Transistors (MODFETs) have gained much attention in recent years because of their ultrahigh speed and inherently low device noise. In this thesis, a novel pseudomorphic MODFET structure has been proposed and realized with a very thin buffer layer and a p-i-n dipole layer. This dipole layers is used to shield the Fermi level pinning effect from the surface of GaAs substrate and minimize the thickness of GaAs buffer layer. For transistors with a gate length of 1.8 μm and drain-to-source spacing of 5μm, but different gate widths, the measured maximum transconductances (gm) are about 300 mS/mm, and the corresponding drain currents are about 220 mA/mm. These measured maximum transconductances (gm) are unusually high for devices with similar scale. These outstand...[ Read more ]

Modulation-Doped Field Effect Transistors (MODFETs) have gained much attention in recent years because of their ultrahigh speed and inherently low device noise. In this thesis, a novel pseudomorphic MODFET structure has been proposed and realized with a very thin buffer layer and a p-i-n dipole layer. This dipole layers is used to shield the Fermi level pinning effect from the surface of GaAs substrate and minimize the thickness of GaAs buffer layer. For transistors with a gate length of 1.8 μm and drain-to-source spacing of 5μm, but different gate widths, the measured maximum transconductances (gm) are about 300 mS/mm, and the corresponding drain currents are about 220 mA/mm. These measured maximum transconductances (gm) are unusually high for devices with similar scale. These outstanding performances are due to the high carrier concentration in 2-dimensonal electron gas (2-DEG) channel and improved carrier confinement provided by high energy barrier due to the p-i-n dipole layer.