Re-growth of transistors on implanted InP

We have developed a process for the re-growth of InP-DHBTs on selectively implanted subcollectors for the purpose of reducing the base-collector capacitance. Si⁺ sub-collector implants were performed at >200degC to minimize damage, an important criterion for achieving smooth morphologies in the re-grown devices. Spectroscopic ellipsometry was used to gauge the amount of implant-induced damage in InP. The wafers were annealed in a MOCVD system in a PH₃ ambient to activate the implanted Si dopant. DHBT re-growths on wafers processed under the optimal implant, annealing and re-growth conditions exhibited smooth morphologies. For these wafers, the field region of the re-grown transistor was indistinguishable from re-growth in the implanted region, when observed under a Nomarski optical microscope. Using the selective implant and re-growth process we have demonstrated significant reduction of the base collector capacitance in InP DHBTs. The base-collector capacitance was reduced by a factor of two over the standard mesa device with full overlap between heavily doped base and sub-collector regions