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 simila
r 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 na
nocrystals embedded in the pores are responsible for the orange-green PL ba
nd. (C) 1999 American Institute of Physics. [S0021-8979(99)05213-5].