Ballistic-electron-emission spectroscopy

Ballistic electron-emission spectroscopy (BEES) and microscopy (BEEM) have been carried out on epitaxial metal/semiconductor interfaces and on epitaxial nanostructures in UHV and at low temperatures. We describe how the band structure of the metal may lead to pronounced focusing of the hot carrier beam injected by the scanning tunneling microscope (STM) tip, thereby greatly enhancing the spatial resolution, such that spectroscopy at buried point defects becomes possible. The strain fields of Ge quantum dots buried underneath an epitaxial silicide film on a Si(100) substrate are found to induce a characteristic clustering of linear defects at the metal/semiconductor interface. The Schottky barrier height lowering associated with these defects allows for an easy identification of buried dots, despite the many mechanisms leading to contrast in BEEM images.