AlGaAs/GaAs heterojunction bipolar transistors with small size fabricated by a multiple self-alignment process using one mask

A multiple self-alignment process for HBT´s using one mask is developed to form emitters, emitter contacts, emitter contact leads, buried small collectors, base contacts, and base contact leads. This process makes it possible to produce HBT´s of very small size and to reduce parasitic elements. An AlGaAs/GaAs HBT fabricated by the process, with an emitter 1 × 20/µm²in size and a buried collector by O⁺implantation gives a good performance of ft= 54 GHz and fmax= 42 GHz. The performance may be explained by the reduction of parasitic elements, base transit time, and collector depletion layer transit time.