Optical absorption, photo-luminescence and miniband formation of a highly ordered and dense 2-dimensional array of Si nanodisks for quantum dot solar cells

We fabricated a highly ordered and dense 2-dimensional array of Si nanodisks (NDs) with our new processes using a bio-template and damage-free neutral beam. Direct-bandgap-like photon emissions were observed from the Si-NDs due to quantum confinement by using time resolved PL measurements. The PL time-profiles were identified in three components (nanosecond region or less) originated in lateral coupling of wave-function i.e. miniband state and localized state in silicon nanodisks. Furthermore, The I-V characteristics of the 2D array of Si-NDs using conductive atomic force microscopy (AFM) indicated that the electronic states of the neighboring NDs were coupled and formed minibands in the 2D array. We also fabricated Si-NDs with an inter-layer of SiC, and found that the SiC matrix could yield a high absorption coefficient without any shift in the bandgap energy (Eg) of the Si-ND structure.