Si surface band-gap shift on top of buried Ge quantum dots

Ge dots grown by molecular beam epitaxy on Si(100) substrates and subsequen tly capped with a IO-nm thick epitaxial Si layer were investigated by means of in-situ scanning tunneling microscopy (STM), scanning tunneling spectro scopy (STS) and ballistic electron emission microscopy (BEEM). At the well- ordered and mostly flat Si surface, protrusions up to 0.35 nm in height wer e found at a density equal to the island density before capping. Additional ly, holes caused by a directed Si diffusion away from highly strained regio ns could be observed. The lateral in-plane strain was determined from the e lastic deformations measured by STM. Due to this inhomogeneous strain a cha nge of the electronic surface structure occurs, resulting in a lowering of the surface band-gap on top of the buried islands. It was also possible to detect the buried islands by BEEM even though no more protrusions could be found on the surface of an additionally deposited CoSi2 film. (C) 2000 Else vier Science B.V. All rights reserved.