Breakdown mechanisms limiting the operation of double doped PHEMTs scaled into sub-100 nm dimensions

The breakdown limit of pseudomorphic high electron mobility transistors (PHEMTs) with double delta-doping structure scaled down into sub-100 nm dimensions is extensively investigated by Monte Carlo device simulations. The two mechanisms responsible for breakdown are channel impact ionization and tunnelling from the gate. The double doped PHEMTs may have two possible placements of the second delta doping layer: either below the channel or between the gate and the first delta doping layer. Quantum mechanical tunnelling starts at very low drain voltages but quickly saturates, having a greater effect on those PHEMTs with the second doping layer placed above the original doping. The threshold for impact ionization occurs at larger drain voltages which should assure the reliable operation voltage scale of double doped PHEMTs. Those double doped PHEMTs with the second delta doping layer placed below the channel deteriorate faster with the reduction of the channel length due to impact ionization than those devices with the second doping layer above the original doping.