CROSS-SECTIONAL TRANSMISSION ELECTRON-MICROSCOPY STUDY OF SI SIGE HETEROJUNCTION BIPOLAR-TRANSISTOR STRUCTURE GROWN BY ULTRA-HIGH-VACUUM CHEMICAL-VAPOR-DEPOSITION/

Si/SiGe heterojunction bipolar transistor (HBT) structure: grown by ul tra-high vacuum chemical vapor deposition (UHVCVD), was investigated w ith cross-sectional transmission electron microscopy (XTEM). It was de termined that a very thin layer exists in the strained SiGe layer grow n on Si; which is in parallel to the interface of SiGe and Si, and the position of thin layer changes with the intrinsic SiGe spacer width b ut not with the Ge content in the strained SiGe base layer. The base c ollector junction turn-on voltage of the HBT decreases from similar to 0.6 V to similar to 0.2 V when the spacer width decreases from 100 A to 75 A, and increases from similar to 0.2 V to similar to 0.4 V when the Ge content in the strained SiGe base layer decreases from 16% to 1 0%. A possible explanation for this phenomenon is that the Ge atom acc umulates to form a very thin Ge-rich layer.