Optical Nonlinearities Due to Carrier Transport in Semiconductors

This paper describes a new class of optical nonlinearities which can be important in semiconductors. This nonlinearity relies on the motion of optically-excited carriers due to internal fields within the semiconductor. Such fields can exist. for example. in semiconductor depletion regions. The charge motion sets up a resultant space charge which acts opposite to the internal fields, reducing their value. The resultant decrease in electric field changes the absorption and/or refractive index through electro-absorption, electro-refraction, electro-optic effect or quantum confined Stark effect, depending on the geometry. To understand these new nonlinearities, we draw from concepts of photorefractivity, n-i-p-i structures, the quantum confined Stark effect (QCSE) in multiple quantum wells (MQW), and relations to the self-electro-optic effect device (SEED).