Vertical scaling of ultra-high-speed AlInAs-GaInAs HEMTs

The scaling of the vertical dimensions of 0.15- mu m-gate-length Al/sub 0.48/In/sub 0.52/As-Ga/sub 0.47/In/sub 0.53/As high-electron-mobility transistors (HEMTs) to reduce their well-known excessive gate leakage current, premature breakdown voltage, and poor output conductance is discussed. It is found that, with a proper choice of doping densities and layer thicknesses, it is possible to realize very-high-performance AlInAs-GaInAs HEMTs (f/sub T/=160 GHz, f/sub max/=300 GHz for 0.15- mu m*50- mu m devices) with low gate leakage current, high breakdown voltage (7.0 V), and very low DC output conductance (45-mS/mm). The DC output conductance exhibits a very strong dependence on the AlInAs doping-thickness product and appears to be a limiting factor in the device power gain. By reducing the doping-thickness product, it was possible to reduce the output conductance by a factor of 3 and thus increase the power gain cutoff frequency by a factor of 1.7.<
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