Orange-green emission from porous Si coated with Ge films: The role of Ge-related defects

Photoluminescence (PL) spectra of porous Si (PS) coated with Ge films were examined using the 514.5 nm line of Ar+ laser. A new orange-green PL band, centered at 2.25 eV, was observed with full-width at half-maximum of similar to 0.1 eV, in addition to the reported PL bands at 3.1, 2.0, and 1.72 eV. With increasing the thickness of Ge layer coated, the new PL band remains unchanged in peak energy but drops abruptly in intensity. Spectral analysis and some experimental results from Raman scattering and x-ray diffraction indicate that Ge-related defects at the interfaces between PS and the Ge nanocrystals embedded in the pores are responsible for the orange-green PL band. (C) 1999 American Institute of Physics. [S0021-8979(99)05213-5].