LOW-POWER EXCITON-BASED HETEROJUNCTION BIPOLAR-TRANSISTORS FOR THRESHOLDING LOGIC APPLICATIONS

Abstract

The principles of an integrated optoelectronic controller-modulator device, based on excitonic transitions and the enhanced Stark effect in quantum wells, are outlined. The device consists of a controller and a modulator as components. The controller is a heterojunction phototransistor with multiquantum wells incorporated in the base-collector depletion region. The amplified output of the controller enables switching of the modulator for low optical power levels. Experimental results on GaAs-AlGaAs based devices, realized by one-step molecular beam epitaxy and selective etching, are presented. The bipolar devices have current gain approximately 35-40. The integrating-thresholding properties of the device are demonstrated and switching characteristics for 10-mu-W input to the controller are measured. Cascadability, optoelectronic amplification, and multistage operation are demonstrated in terms of a fan out of eight devices. The integrating-thresholding properties also lend themselves to the implementation of neurons and to the realization of decision making processes. The controller-modulator device can form a versatile basic module for optical computation architectures.