Delay time analysis for 0.4- to 5- mu m-gate InAlAs-InGaAs HEMTs

InAlAs-InGaAs HEMTs with 0.4- to 5- mu m gate lengths have been fabricated and a maximum f/sub T/ of 84 GHz has been obtained by a device with a 0.4- mu m gate length. A simple analysis of their delay times was performed. It was found that gradual channel approximation with a field-dependent mobility model with E/sub c/ of 5 kV/cm holds for long-channel devices (L/sub g/>2 mu m), while a saturated velocity model with a saturated velocity of 2.7*10/sup 7/ cm/s holds for short-channel devices (L/sub g/<1 mu m).<
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