A detailed investigation of in situ-doped polysilicon emitters with interfacial oxide employed in implanted-base Si bipolar junction and epitaxial-base silicon/germanium (SiGe) heterojunction bipolar transistors is presented. In order to tune and control transistor parameters such as current amplification we modify the poly/monocrystalline silicon interface sandwiched between the emitter polysilicon and the base substrate or epitaxy. Various types of interface oxidation were examined and correlated to bipolar device data. We profoundly studied subnanometer silicon oxide growth by rapid thermal oxidation, low-pressure furnace oxidation, and chemical oxidation. Also a combination of thin chemically grown oxides with a thermal postoxidation was characterized. We correlate the oxide thickness to transistor parameters such as current amplification beta. Also, the influence of As-enhanced oxide breakup during different emitter anneals as well as the dependence on annealing parameters on beta was studied. (c) 2005 American Vacuum Society.