Scaling of Stark-Shifted Nonlinearities in Multiple Quantum Well Structures

Abstract

Optical switching and logic devices require a large optical nonlinearity (absorptive or refractive) per absorbed photon (or injected charge), combined with a rapid excitation recovery time. The accumulated absorptive (or index) changes during a laser pulse are proportional to the shorter of either the pulse duration or the excitation lifetime. Optimally the two are matched, in which case the switching energy (power-time product) is determined primarily by the change in absorption coefficient (or refractive index) per photogenerated carrier-pair. Any mechanism, material or structure that will enhance the per-carrier nonlinear response is therefore of considerable interest. Device structures (such as self-electrooptic effect devices (SEED’s), hetero n-i-p-i’s, and piezoelectric multiple quantum wells (MQWs)) that rely on the screening of applied, built-in or intrinsic fields are purported to have large per carrier nonlinearities primarily because the carriers generated in a single well can escape and move to screen multiple wells. As a class, we refer to the nonlinearities in such structures as Stark-shifted nonlinearities, since they arise from a reduction in the quantum-confined Stark effect (QCSE) as the field is screened by the photogenerated charge.