InP-HBTs with good high frequency performance at low collector currents using silicon nitride planarisation

A fabrication process for small area HBTs with a self-aligned base contact has been developed, based on silicon nitride planarisation. The mean current gain for 130 realised devices ranged from 40 for the smallest devices, to 71 for the largest, with a standard deviation of <10%. The transit frequency was 94.7±2.6 GHz, and the maximum frequency of oscillation 95.1±4.4 GHz, at a collector current of only 0.3 mA. The extremely good high frequency performance at low currents and high uniformity improves the competitiveness using InP-based HBTs for fabrication of complex integrated circuits