A METASTABLE STATE IN SELF-ELECTRO-OPTIC EFFECT DEVICES USING STARK LADDER TRANSITIONS

A self-electro-optic effect device (SEED) based on Wannier-Stark local ization in GaAs/AlAs superlattices, can show multiple negative differe ntial resistance (NDR) regions in the photocurrent vs reverse bias vol tage curve. This phenomenon comes from the multiple Stark ladder trans itions, which successively come into resonance with the optical input to the SEED, when the external electric field intensity is varied. Usi ng these multiple NDR regions in a symmetric SEED configuration, we ha ve found, for the first time, a metastable point isolated inside the b istable hysteresis curve of the optical switching characteristics, in the sense that it cannot be reached by conventional CW light quasistat ic intensity variations. Optical tri-state switching via this intermed iate state has been observed in transmission by an optical pulse excit ation method, and can be explained clearly with a novel global stabili ty analysis of differential equations for photocurrents in the symmetr ic SEED system.