Optimization and tolerance analysis of QCSE modulators and detectors

This paper describes the design constraints and optimization of multiple-quantum-well (MQW) devices for use as flip-chip bonded devices on silicon circuitry. These devices act as quantum-confined Stark effect (QSCE) modulators and detectors. It is shown that the optimal device thickness depends upon the biasing voltage levels as well as the voltage swing that is available from the silicon circuitry. Lower voltages favor thinner device designs. It was found that, for GaAs-AlGaAs quantum wells, a design in which the modulator and detector are of identical design, a combined efficiency of 0.36 could be achieved with a 5-V swing on the modulators, falling to 0.21 with 2.5 V. By using separate layers for the design of the modulator and detector, the performance could be improved significantly with 0.48 achievable for a 5-V swing. It is shown that optimizing the device to minimize nonuniformity effects makes the optimal design thinner.