After describing the characterization of heterostructured pn junction and the direction of design for the high speed operation of HBT, I made the HBT using the wafer grown by LPE.
$Si_3N_4$ were used as mask for the fine confinement of Zn. diffusion. The equipment of plasma etching, which was to make the fine pattern, was characterised, and used for the etching of $Si_3N_4$.
C-V curves between emitter and base and base and collector were measured, from which a.c. parameters were derived. So I could derive the maximum of frequency from it as well as various process parameters.