Stepped versus square multiple-quantum-well modulators

Several authors have demonstrated that quantum well (QW) structures in which the quantum well is graded, stepped, or otherwise modified from the standard square geometry can have an improved quantum-confined Stark effect (QCSE). However, relatively few of these structures have been studied in geometries containing sufficient quantum wells for real modulator use. Here, we report the experimental study of 60-period multiple-quantum well (MQW) structures with photocurrents and in transmission. We have experimentally compared QW geometries containing single- and double-step structures to a standard square QW.