Visible and Infrared Photoluminescence from Deposited Germanium-Oxide Clusters and from Ge Nanocrystals

Abstract

Following Canham’s report of visible photoluminescence (PL) from porous silicon,1 the optical and electronic properties of nano-structures made from silicon (Si) or germanium (Ge) have attracted much attention, because they open a new possibility for photonic applications by the use of group-IV elements. In particular, PL properties of Si nanocrystals (nc-Si) have been widely studied and the relationship between the size of nc-Si and the PL peak energy has been revealed experimentally for at least red and near-infrared (NIR) PL.2–4 According to these reports, nc-Si with about 4 nm in diameter exhibits a PL peak at about 1.4 eV. As the size decreases further, the PL peak shifts to higher energies and reaches the visible region for nc-Si smaller than 2 nm. In contrast to nc-Si, there have been few reports on the size dependence of the PL spectra for Ge nanocrystals (nc-Ge). The nc-Ge has been prepared by several methods and these samples exhibit strong visible PL at about 2.2 eV independent of the size of nc-Ge (2–15 nm) and the preparation methods.5–11