Modeling of a low-intensity electro-optical semiconductor switching device due to intrinsic photoconductivity

Abstract

An electro-optical device consisting of a stack of undoped alternating layers of narrow- and wide-gap materials (e.g., GaAs/AlGaAs) together with a series resistor under constant voltage bias is analyzed theoretically. The GaAs heterolayers with a width in the order of a carrier mean free-path are a photo-active region of this vertical device. The device operates only in the presence of a low-intensity light beam due to the intrinsic photoconductivity of the active region. The Franz–Keldysh effect, the strong accumulation of the photocarriers in the photo-active layers due to the charge separation in the presence of the static electric field, and the ballistic component of the total current are responsible for the unusually large electro-optical nonlinearity of the device. Kirchhoff’s law for the electrical circuit of the device provides a sensitive feedback between the voltage drop over the layer and the photocurrent. In a Fabry–Perot cavity a room temperature electro-optical bistabitity is obtained at light intensities less than 10 mW/cm2 with a switching time of about 100 ns.