Lateral p/sup +//p regrown base contacts for AlGaAs/InGaAs HBTs with extremely thin base layers

Summary form only given. Selective regrowth of heavily C-doped p+-GaAs contact layers drastically reduces base resistance Rg of HBTs, giving high-f/sub max/ above 200 GHz for HBTs with planar p/sup +//p regrown contact (PC) structures. This paper describes an advanced regrown base structure with high process controllability as well as excellent microwave performance. In this structure, the regrown contact layer is in lateral contact (LC) with an intrinsic base layer and enables the access to extremely thin base layers without delicate base exposure processes, This LC structure was used for HBTs with thin (60, 40 nm-thick) graded-InGaAs base layers for the first time. Excellent device performance was achieved: a dc current gain more than 100, a base transit time /spl tau//sub B/ shorter than 0.2 ps, and an f/sub max/ of 208 GHz. Unlike the PC structure, the LC structure with the thin and graded base has a reduced contact area and GaAs/InGaAs heterostructure interface. To evaluate the effect of this LC structure on device performance, detailed analysis was carried out on the contact resistance and recombination current at the regrowth interface.