A bipolar transistor structure and a method for fabricating the bipolar transistor structure include: (1) a collector structure located at least in-part within a semiconductor substrate; (2) a base structure contacting the collector structure; and (3) an emitter structure contacting the base structure. The interface of the emitter structure and the base structure includes an oxygen impurity and at least one impurity selected from the group consisting of a fluorine impurity and a carbon impurity, to enhance performance of a bipolar transistor within the bipolar transistor structure. The impurities may be introduced into the interface by plasma etch treatment, or alternatively a thermal treatment followed by an anhydrous ammonia and hydrogen fluoride treatment, of a base material from which is comprised the base structure.