Investigation of single boron accepters at the cleaved Si : B(111) surface

The cleaved and (2X1) reconstructed (111) surface of p-type Si is investiga ted by scanning tunneling microscopy (STM). Single B accepters are identifi ed due to their characteristic voltage-dependent contrast, which is explain ed by a local energetic shift of the electronic density of states caused by the Coulomb potential of the negatively charged acceptor. In addition, det ailed analysis of the STM images shows that apparently one orbital is missi ng at the B site at sample voltages of 0.4 - 0.6 V, corresponding to the ab sence of a localized dangling-bond state. Scanning tunneling spectroscopy ( STS) confirms a strongly altered density of states at the B atom due to the different electronic structure of B compared to Si.