Full-wave electromagnetic modelling of an InP/InGaAs travelling-wave heterojunction phototransistor

Three-dimensional full-wave electromagnetic analysis of a travelling-wave heterojunction phototransistor (HPT) is presented. Employing the finite-difference time-domain method and run on a fast, parallel processing machine the simulation herein allowed, for the first time to our knowledge, the simultaneous investigation of the optical and electrical characteristics of the travelling-wave structure. Snapshots of the field propagation inside the device provide valuable insight into its passive behaviour and conclusively demonstrate the velocity mismatch between the optical wave and the photo-enerated electrical signal. Numerical results are presented for the device's output characteristic impedance, photocurrent and effective refractive indices of the optical and electrical signal that quantify the difference in the velocities of the two waves. Moreover, results obtained from the method's initial test in the simulation of an asymmetric planar optical waveguide, similar to the one integrated within the HPT's structure, compare very favourably with the theory.