Low-temperature UV photoluminescence of ion beam synthesized Si nanoclusters embedded in Si

Ultraviolet (UV) photoluminescence (PL) data taken on a double Au implanted Si matrix are reported. This has been studied over a wide temperature range of 28-220 K. At low temperature, the spectrum shows four peaks corresponding to a zero-phonon line (ZPL) and three low-energy phonon-assisted lines. At 28 K the ZPL has an energy of 3.362 eV with a lifetime of ~240ps suggesting transitions across a direct gap. The temperature variation of the ZPL intensity indicates an activation energy ~10 meV comparable to the binding energy of excitons in crystalline Si (c-Si). For T>100 K, it shows a redshift which can be understood as coming from exciton-phonon interaction. At lower temperatures the corresponding line broadening shows evidence of interaction with low-energy phonons of average energy ~7 meV as suggested earlier. All the above results indicate the emission to be coming from Si nanoclusters (NCs) embedded in the matrix.