AVS 45th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM5
Ultra-high B and As Doping during Si(001) Gas-Source Molecular Beam Epitaxy: Growth Kinetics, Dopant-Incorporation, and Electrical Activation

Tuesday, November 3, 1998, 9:40 am, Room 308

Session: Semiconductor Surface Structure
Presenter: G. Glass, University of Illinois, Urbana-Champaign
Authors: G. Glass, University of Illinois, Urbana-Champaign
H. Kim, University of Illinois, Urbana-Champaign
A. Vailionis, University of Illinois, Urbana-Champaign
J. Soares, University of Illinois, Urbana-Champaign
P. Desjardins, University of Illinois, Urbana-Champaign
J.E. Greene, University of Illinois, Urbana-Champaign
Correspondent: Click to Email
Si(001) layers doped with B or As were grown on Si(001)2x1 substrates by gas-source molecular-beam epitaxy using Si@sub 2@H@sub 6@, B@sub 2@H@sub 6@, and AsH@sub 3@ at temperatures T@sub s@ = 500-850 °C. Dopant concentrations ranged from 1x10@super 16@ to 1.2x10@super 22@ cm@super -3@ for B and 1x10@super 16@ to 1x10@super 18@ cm@super -3@ for As. B incorporation was linear with incident B@sub 2@H@sub 6@/Si@sub 2@H@sub 6@ flux ratio for B concentrations C@sub B@ @<=@ 2.5x10@super 20@ cm@super -3@, and increased with higher flux ratios. As incorporation was linear to 3x10@super 17@ cm@super -3@, and subsequently was sub-linear. At T@sub s@ = 550 and 600 °C, B was incorporated into substitutional electrically-active sites for C@sub B@ up to 2.5x10@super 20@ cm@super -3@. At higher B concentrations, there is a large and discontinuous decrease in the electrically active fraction of B, although the total activated B concentration continues to increase. Hall-effect measurements show the As to be fully electrically active for all films in the study. All films were fully strained. TEM investigations revealed that B doped films grown at T@sub s@ @<=@ 600 °C, and all As doped films were highly perfect with no indication of precipitates or dislocations. Deuterium temperature-programmed desorption measurements as a function of increasing C@sub B@ and C@sub As@ show strong surface segregation. The B deactivation behavior can be explained on the basis of a model which accounts for strong B segregation to the second-layer, and the surface formation and subsequent incorporation of electrically inactive B-dimers at higher C@sub B@ values. In contrast, As acts to passivate the surface, resulting in arrested growth as the As coverage approaches 1 ML. The combination of HR-XRD, SIMS and Hall-effect measurements, show that the Si-B bond length due to B-dimers is 1.99 Å, compared to 2.04 Å for substitutional B atoms.