Optically induced and charge-transport-assisted electroabsorptive and electro-optic nonlinearity in cadmium telluride

Abstract

We have observed the optically triggered formation of a high electric field region underneath the negative electrode. The optical control of the magnitude and the position of this field build-up, typically 10 to 20 times the applied field, combined with the electro-optic or the Franz-Keldysh effect, provides a novel large optical nonlinearity. The high field region (0.1-0.2 mm wide) forms in few microseconds upon illumination by below bandgap light (860-900 nm) and persist in the dark with a latch time of 2-5 s. This effect is highly sensitive, requiring approximately 10 nJ/cm2 absorbed fluence, and exhibits an intensity and applied voltage dependent response time. Furthermore, this high field can be erased by illuminating the region through ITO electrodes with near bandgap light (835-nm GaAs laser diode). This field buildup and erasure can be used in a variety of device configurations (one- or two- dimensional arrays, self switching or two wavelength schemes) for opto-optical switching and spatial light modulation applications. These devices can benefit from the large electro-optic coefficient of CdTe (5–6 pV/m) for high contrast polarization switching, or taking advantage of the high electric fields, use the observed Franz-Keldysh electro-absorption which provides large absorption and the associated refractive index changes.