OPTICAL-PROPERTIES OF ULTRATHIN CRYSTALLINE AND AMORPHOUS-SILICON FILMS

The complex dielectric functions 2<hν<4 eV of ultrathin crystalline silicon c-Si and amorphous silicon a-Si:H films consisting of isolated clusters have been measured at 250°C by real time spectroellipsometry. For c-Si cluster films ∼12 Å thick, a well-defined absorption onset near 3 eV is observed that blueshifts with decreasing thickness, consistent with quantum confinement of electrons. A much broader absorption onset is observed for a-Si:H cluster films of similar thickness and is attributed to an electron mean free path less than the cluster size, which limits the observation of confinement effects. © 1995 The American Physical Society.