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/µm
²
in size and a buried collector by O
⁺
implantation gives a good performance of f
t
= 54 GHz and f
max
= 42 GHz. The performance may be explained by the reduction of parasitic elements, base transit time, and collector depletion layer transit time.