Reduction of short channel effects in self-aligned AlInAs/GaInAs HEMTs by lateral bandgap engineering for high f/sub max/

Advances in materials and processing technology have made possible the fabrication of HEMTs with f/sub /spl tau// as high as 340 GHz (f/sub max/=250 GHz). However it is difficult to simultaneously obtain a high f/sub /spl tau// and f/sub max/. This is because a high f/sub /spl tau// requires a self-aligned FET structure. However the reduced source-drain separation results in short channel effects like drain induced barrier lowering and high output conductance. Also the gate-drain capacitance Cgd is increased. This reduces the f/sub max/ of the device. In this abstract we present a novel lateral bandgap engineering technique which reduces the short channel effects in a self-aligned HEMT and makes it possible to achieve a f/sub max/ in a high f/sub /spl tau// FET structure.