Optimization of InAlAs/InGaAs heterostructure field effect transistors for an application in optoelectronic receivers

The authors investigate the influence of the layer sequence on transconductance, leakage current, gate-source capacitance, and current gain cut-off frequency and the optimization of InAlAs/InGaAs HEMTs (high electron mobility transistors) for application in optoelectronic receivers. A medium sheet concentration range around 3.0 to 3.5*10/sup 12/ cm/sup -2/ seems to be a good compromise between high-frequency behavior, system sensitivity, and technical aspects for 1- mu m gate length HEMTs. In that range one observes no strong dependence of the leakage current, transit frequency, and gate-source capacitance on the carrier sheet concentration. Further lowering of the doping level and/or a simultaneous increase in doping layer thickness is problematic since the gate to channel distance has to be increased and the contribution of the doping layer to the 2-D electron gas (2DEG) becomes less effective. On the other hand the processing of a wafer with lower doping levels is less critical with respect to the gate recess control. The thermal stability of these layers will be improved also.<>