High-gain InGaAs heterojunction phototransistor operating at 930 nm using resonant periodic absorption for surface-emitting laser logic devices

Abstract

Using a new technique called resonant periodic absorption, we have achieved high-optical gain in InGaAs/GaAs heterojunction phototransistors (HPTs) for wavelengths at which GaAs substrates are transparent(>925 nm). These devices are promising for optoelectronic interconnect, optical-logic device, neural network, and lightwave communication uses. Specifically, these InGaAs HPTs are ideally suited for integration with InGaAs vertical cavity surface-emitting laser (VCSEL) diodes to produce monolithic surface-emitting laser logic (CELL) devices.1 Resonant periodic absorption is achieved in an asymmetric microresonator consisting of a strained layer InGaAs/GaAs HPT sandwiched between distributed Bragg reflectors. By aligning the optical intensity maxima with the InGaAs quantum wells in the collector region of the phototransistor, we are able to achieve high gain(>600 at a 4.0-V bias and a 50-mA collector current) at wavelengths >900 nm from a structure in which the absorption coefficient, aL, is only ~0.1. We describe the design, growth, and fabrication of a monolithic CELL consisting of an InGaAs/GaAs HPT and VCSEL operating at 930 nm. CELL devices are cascadable optical logic devices (smart pixels) in which incident light generates photocurrent in the phototransistor that is internally amplified and then used to drive the VCSEL above threshold. These devices will operate at a wavelength that is in the passband of the GaAs substrate and therefore avoid the problems associated with the removal of the substrate in AlGaAs/GaAs CELL structures operating in transmission.