Electron microscopy of the ordered boron 2 × 1 structure buried in crystalline silicon

The fabrication of an ordered dopant distribution within a semiconductor provides an exciting challenge to thin-film growth. In this paper the structure of an ordered boron layer embedded in silicon is analyzed by electron microscopy. Planar-transmission electron diffraction confirms preservation of the 2 × 1 ordered boron layer beneath the crystalline Si cap. High-resolution transmission electron microscopy in cross-section clearly identifies the BSi layer and shows that the width of this layer in the growth direction is ≤ 5 monolayers (ML). This confirms earlier X-ray diffraction and Auger electron spectroscopy results which determined the boron spreading to be ∼ 3 ML. Secondary ion mass spectroscopy results, showing a resolution-limited impurity profile, are also included. Plan-view imaging is used to identify defects in the structure. These results provide further insight into this unique dopant structure which yields the narrowest electrically active dopant profile reported.