Fundamental limitations of InP MISFET due to Gunn oscillations

The strong bulk negative differential resistivity (NDR) exhibited by InP, causing instabilities and limiting performance, is investigated using a 2-D hydrodynamic energy model. A study of drain current instability shows that it occurs more easily in MISFETs than in GaAs MESFETs, and that the maximum usable doping level decreases when the ratio L/sub g//a decreases. This can be related to the fact that in a MISFET the gate control is less effective than in a MESFET, as previously show, and the NDR in InP is more important than in GaAs. For a planar uniformly doped structure, oscillations occur for very low N/sub d/a product and give low current values. For power amplification, a nonuniform doping profile with overdoping between gate and drain contact has been used to obtain stable operation. Such a solution may involve other limitations due to the breakdown mechanism and parasitic capacitances.<>