Microscopy and spectroscopy of buried nanostructures

Ballistic-electron-emission microscopy (BEEM) has been performed on epitaxi al CoSi2/Si(111) and CoSi2/Si(100) films, and on CoSi2/Si/Ge/Si(100) hetero structures containing buried Ge quantum dots. At CoSi2/n-Si(111) and CoSi2/ p-Si(111) interfaces the spatial variation of hot carrier transmission is d ominated by scattering at dislocations and point defects, while the Schottk y barrier height is not measurably affected by defects. The excellent spati al resolution of 1.3 nm, achieved for films as thick as 5 nm on n-Si(111) a nd of 1.6 nm on p-Si(111) can be explained only by taking into account the theoretically predicted focussing effect of the hot electron beam, induced by the special constant energy surfaces of CoSi2. Scanning tunneling spectr oscopy (STS) studies of Ge quantum dots buried in a Si matrix have revealed a substantial lowering of the Si surface band gap due to the strain impose d by the dots. In CoSi2/Si/Ge/Si(100) heterostructures the Ge-induced strai n has been found to modify the defect structure at the CoSi2/Si interface, leading to pronounced contrast variations in BEEM images. The BEEM contrast gives direct evidence for the rotation of Ge islands by 45 degrees during capping with epitaxial Si. (C) 2000 Elsevier Science B.V. All rights reserv ed.