OBSERVATION OF P DONORS ON THE SI(111) SURFACE BY SCANNING-TUNNELING-MICROSCOPY

We report on the individual observation of substitutional P donors on the reconstructed Si(111) 2 x 1 surface by means of scanning tunneling microscopy and tunneling spectroscopy. Depending on the scanning volt age, the dopants give rise to different features superimposed on the b ackground lattice. This is explained by the influence of the charged P atom on the electronic surface-states resulting in a local band shift . The spatial arrangement of the donors obeys a statistical distributi on, excluding significant clustering even at a P concentration of 6 x 10(19) cm(-3) which is far above the metal-insulator transition.