DESIGN OPTIMISATION OF ULTRA-SHORT GATE HEMTS USING MONTE CARLO SIMULATION

By using a Monte Carlo simulator the static and dynamic characteristics of a 50 nm gate AlInAs/GaInAs δ−doped HEMTs are investigated. The Monte Carlo model includes some important effects that are indis-pensable when trying to reproduce the real behaviour of the devices, such as degeneracy, presence of surface charges, T-shape of the gate, presence of dielectrics and contact resistances. Among the large quantity of design parameters that enter into the fabrication of the devices, we have studied the influence on their per-formance of two factors: the doping level of the δ-doped layer and the length of the recess. We will show that the first one has a very important effect on the cutoff frequency and other important figures of merit of the transistor, and its value has to be carefully chosen. Conversely, we have also checked that the influence of the recess length is quite slight