Study of edge-coupled waveguide InGaAs/InP heterojunction phototransistors for microwave applications

Heterojunction phototransistors (HPTs) are promising devices for high-performance optical fibre telecommunication systems for digital or microwave applications at long wavelengths (1.3 and 1.55 μm) They simultaneously detect and amplify an optical signal, thus combining the functions of a PIN photodiode and a HBT. Unlike avalanche photodiodes they exhibit an internal gain owing to transistor effect without high bias voltage and excess noise due to impact ionisation. First results obtained with two-terminal HPTs demonstrated the ability for these devices to exhibit gain up to 30 GHz and to perform optical-optical or electro-optical mixing. Due to the attractive properties of these devices for microwave and millimetric applications, we present a theoretical analysis of 2T and 3T devices, including comparison with experimental results. First, we present the device and the modelling tools that we developed in order to study and optimise: an optical model and an electrical model. Then we present the results of this study. (6 pages)