Effect of a Step Barrier on the Quantum-Confined Stark Effect and Applications to Electroabsorption Modulators with High Saturation Optical Power

Abstract

The effect of a step barrier on the quantum-confined Stark effect (QCSE) is examined theoretically. We use a InGaAsP/InGaAsP quantum well (QW) as the basis structure and compare it with QWs having different step-barrier heights and widths. Since the step barrier delays the red shift of the QCSE when the electric field is applied from the well to the step barrier, QWs with step barriers can be used for high-optical-power operation. The reason behind the high-optical-power operation is that the high electric field facilitates the sweep-out of photogenerated carriers in the QW, thus reducing the charge screening effect. A wider step barrier is also shown to have an earlier onset of the red shift, thereby increasing the amount of red shift at a given field. Hence, the electroabsorption modulators with wider-step QWs can be used to increase the slope of the transfer curve and to reduce the residual absorption when a higher detuning energy is used.