Design and realisation of InP-HBTs for optical telecommunications

Microwave InP/InGaAs HBTs are fabricated and tested using materials grown by MOCVD. The characteristics of these devices with spacer layers are studied using an analytical model, combining the thermionic-field-emission (TFE) process at the B/E hetero-interface and the diffusion current in the quasi-neutral region. Good agreement was found between the experimental data and the theoretical predictions. To demonstrate the suitability of using InP-based HBTs for low power analogue applications, we compared the turn-on voltages of the InP/InGaAs HBTs with typical GaAs-based HBTs as well as with the commercial Si bipolar transistors. The results obtained showed clearly that, among all the material systems studied, the InP/In_0.53Ga_0.47As MBTs have the lowest turn-on voltage (0.2 V). This is in good agreement with the theoretical prediction. InP-HBTs with modest emitter geometries demonstrated a cut-off frequency of 32 GHz. We also measured the spectral responses of these transistors and compared them with the theoretical data