Optimum design and fabrication of InAlAs/InGaAs HEMT's on GaAs withboth high breakdown voltage and high maximum frequency of oscillation

A simple model to describe the dependence of the breakdown voltage between gate and drain on width of the gate recess in an InAlAs/InGaAs high electron mobility transistor (HEMT) is presented. In this model, the depletion region laterally spreads to the drain region. It enables us to express the dependence of device parameters on the width of the gate recess. The model suggests that the breakdown voltage increases with the width of the gate recess and then saturates, which is experimentally confirmed. Calculations based on the model show that the maximum frequency of oscillation (f_max) also increases with the width of the gate-recess due to the reduction in both the drain conductance and the gate-to-drain capacitance, and then slightly decreases with the width due to the increase in the source resistance. We fabricated InAlAs/InGaAs HEMT's lattice-mismatched on GaAs substrates with optimum recess-width, and these exhibited both a high breakdown voltage of 14 V and a high f_max of 127 GHz at a gate length of 0.66 μm