PL spectra of a-SiOx with 39 at. % < [Si] < 59 at. %. (a) The initial spectra shift to the blue spectral range with decreasing Si content. (b) After degradation, the emission maxima coincide at E PL,deg = 2.16 eV for [Si] < 47 at. %. The spectrum of the sample with [Si] = 59 at. % is not affected by the degradation.
Summary of emission maxima E PL of both initial and degraded PL-spectra. The spectral degradation restricts the emission maxima to E PL,deg < 2.16 eV. The emission maxima of samples with E PL,ini < 2.16 eV are not affected by the spectral degradation. Most other publications did not report on luminescence of a-SiOx above E PL = 2.16 eV. 3,13,23 Probably, spectral degradation for these samples already occurred before the PL measurements.
Measured initial (solid curves) and modeled (dotted curves) PL spectra. The modeled spectra calculate from E 04 and E 0 according to the band tail luminescence model (Eq. (1) ). Both measured and modeled spectra agree well in E PL and the spectral shape. The overestimation of the low energetic and the underestimation of the high energetic shoulder are in accordance with the explanatory approach.
The measured and modeled initial PL spectra differ in shape. The overestimation of the low energetic ΔΦLE shoulder arises from (a) non-radiative recombination via defect states. The underestimation on the high energetic ΔΦHE side results from (b) the excitation of defect states and (c) the contribution of change carriers excited above the conduction band edge.
Initial (dashed curves) and degraded (solid curves) PL spectra replotted from Figures 1(a) and 1(b) . (a) For samples with E PL,ini > 2.16 eV, the degradation causes a redshift by ΔE PL. The degraded spectra share a common maximum around E PL,deg ≈ 2.16 eV. The sample with [Si] = 47 at. % remains unchanged since E PL,ini ≈ E PL,deg ≈ 2.16 eV. (b) In the spectra of samples with E PL,ini < 2.16 eV, a high-energetic shoulder emerges. The difference between degraded and initial spectra (dotted curves) unveils that this recombination center has the same energy E PL ≈ 2.16 eV. The sample with [Si] = 59 at. % remains unaffected by the spectral degradation.
The impact of Si = O on the degradation depends on the density of emerging trap states. The density of Si = O states is schematically represented by the red and blue bars. The higher the oxygen content, the higher is the density of Si = O trap states. For [Si] < 47 at. %, excited charge carriers are trapped at the Si = O states. Recombination is dominated by these localized states. In the range 51 at. % < [Si] < 55 at. %, only few excitons are trapped at the Si = O states. For [Si] > 59 at. %, the density of Si = O states is too low to affect the initial luminescence mechanism.
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