We repalt the fabrication by PECVD of silicon-rich erbiumdoped silica films that exhibit both 1535 nm f%" and visible photoluminescence. Fluorescence spectra are presented along with absorption spectra that display a strong band edge in the blue, which we ascribe to the presence of Si microclusten. We are unable to observe chamcteristic E?+ absorption bands and propase that excitation of the rare e h is via an energy transfer pmcess from Si microciusters.

We have carried out a study of the photoluminescence properties of silicon-rich silica. A series of films grown using plasma enhanced chemical vapor deposition over a range of growth conditions were annealed under argon at selected temperatures. Photoluminescence spectra were measured for each film at room temperature and for selected films at cryogenic temperatures. The photoluminescence spectra exhibit two bands. Fourier transform infrared and electron spin resonance spectroscopies were used to investigate bonding and defect states within the films. The data obtained strongly suggest the presence of two luminescence mechanisms which exhibit different dependencies on film growth conditions and postprocessing. We make assignments of the two mechanisms as ͑1͒ defect luminescence associated with oxygen vacancies and ͑2͒ radiative recombination of electron-hole pairs confined within nanometer-size silicon clusters ͑''quantum confinement''͒.

We present a model for the luminescence spectrum of silicon nanoclusters. We propose that the major contribution to luminescence is from radiative recombination of confined excitons ͑quantum confinement͒. Utilizing the effective mass approximation we consider the variation in oscillator strength with cluster size and the associated change in the number of available free carriers. By varying both the mean cluster size and size distribution of silicon nanoclusters, the luminescence spectra are modeled to a good fit. We compare our model with experimental photoluminescence and electroluminescence data from this group and from others.

We present the results of what we believe to be the first study of the power efficiency of room temperature photoluminescence from thin films of silica containing silicon nanoclusters. Films were prepared by plasma enhanced chemical vapor deposition from silane and nitrous oxide precursors. Luminescence was excited using the 476 nm line of an argon-ion laser. We have measured power efficiencies for samples that exhibit luminescence solely due to radiative recombination of quantum confined excitons. Efficiencies around 0.04% are reported. © 1998 American Institute of Physics. ͓S0003-6951͑98͒03330-0͔Following Canham's report of visible luminescence from porous silicon, 1 there has been an explosion of interest in light emission from novel forms of nanoscale silicon. There have been a number of reports in the literature of visible and near-IR emission from silicon nanoclusters. [2][3][4][5][6] Typically, such clusters lie in the sub-100-Å diameter regime and exhibit a broad red luminescence band similar to that reported from porous silicon. Reports have been published of nanoclusters deposited onto silicon substrates and embedded within dielectric matrices such as silica. There has been much debate over the nature of the luminescence mechanism in this material and contradictory reports of its optical properties, but there is a growing consensus that, in common with porous silicon, quantum confinement of excitons within the nanoclusters plays a significant role. 7-10 Previous work by this group has addressed the nature of the luminescence mechanism and has indicated the presence of two distinct processes: radiative recombination of confined excitons within the silicon nanoclusters and defect luminescence from the surrounding matrix. 7,8 A single unique mechanism does not provide a good enough explanation of the luminescence properties of nanoscale silicon. However, whatever the mechanism, this remains a technologically important material as it makes a significant contribution to the search for a silicon-based light emitting material. For this reason, it is imperative to obtain measurements of luminescence efficiency from nanoclustered silicon. To date, despite the number of reports of luminescence from silicon nanoclusters, there have been no reported studies of luminescence efficiency from this class of material.In this letter we present the results of a study undertaken to measure photoluminescence power efficiencies of thin films of silica containing nanoclustered silicon. The films were produced by plasma enhanced chemical vapor deposition ͑PECVD͒: details of their growth can be found in Ref. 7. Films were 1-2 m thick and were grown on silicon substrates. Photoluminescence was excited using the 476 nm line of an argon-ion laser, and for the purposes of recording spectra luminescence was dispersed through a single-grating Bentham M300 monochromator and detected using a photomultiplier tube. Spectra were corrected for the spectral response of the optical system and the whole apparatus was computer controlled.For m...

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