The fabrication and properties of silicon-nanocrystal-based devices and structures produced by ion implantation - The search for gain

Experiments were undertaken to verify a recent claim of optical gain produced by photo-excited silicon nanocrystals. This was achieved by propagating an optical probe beam (wavelength of 800 nm) through a slab waveguide containing silicon nanocrystals and measuring this signal as the nanocrystals were optically excited by a high energy density (3.5-3500 muJ/cm(2)) pump beam (wavelength 355 nm). The probe signal was observed to decrease when the guide was subjected to optical pumping - no gain was observed. Indeed, the results are shown to be consistent with an excited state absorption process, in which photo-generated carriers induce 'free' carrier absorption. (C) 2003 Elsevier Science B.V. All rights reserved.