Photometric spectra of a series of a-Si:H films obtained by black etching for increasing treatment times tetch showing (a) the total hemispherical reflection spectra and (b) the total hemispherical transmission spectra. The respective spectra of the untreated a-Si:H film are indicated by tetch = 0 s. The initial thickness of all samples was equal to the thickness of the untreated a-Si:H film; after the etching these samples show the coherent optical thicknesses dcoh as indicated.
Total absorption spectra A of (a) the untreated and black-etched a-Si:H films from Fig. 1 and (b) an untreated and black-etched µc-Si:H film. The absorption spectra are calculated from the respective experimental spectra of the total hemispherical reflection R and the total hemispherical transmission T. The spectra of the untreated samples after smoothing of the interference fringes and those of the samples with the longest treatment times are represented by shaded area graphs.
Extended absorption spectra for (a) the series of untreated and black etched a-Si:H films from Fig. 2(a) and (b) the corresponding µc-Si:H films from Fig. 2(b). The data in the low-absorption region are obtained via photothermal deflection spectroscopy (symbols) and are fitted to the photometrical data (solid lines) in the region where αL ≈ 1.
Enhancement of the internal absorption probability due to light trapping in the black-etched (a) a-Si:H and (b) µc-Si:H films from the previous figures. The spectra Ap , represented by symbols, are obtained directly from the experimental data and are linked to the right-hand scale. The solid curves Amax represent the spectra of the maximally achievable absorption in the films investigated according to the theory of statistical light trapping. The experimentally obtained absorption enhancement factors Fe are represented as indicated in the left-hand legend and are linked to the left-hand scale. The respective theoretical enhancement factors Ft are represented by broken lines.
Three-dimensional atomic force microscopy images of (a) an untreated a-Si:H surface, (b),(c) a black-etched a-Si:H surfaces with increasing treatment time tetch , and (d) a black-etched µc-Si:H surface. The variation of the silicon fraction at the air–Si interface of the films as obtained via statistical analysis of the AFM data is shown in the diagram at the right-hand side of each image.
Two-dimensional AFM images (a) of the black-etched a-Si:H sample from Fig. 5(c) and (b) of the black-etched µc-Si:H sample from Fig. 5(d).
Photoconductivity spectra σ ph of a-Si:H films treated by black etching with increasing treatment tetch (a) under illumination of the air-exposed black-etched side of the films and (b) under illumination of the films through the glass substrate.
Stripe illumination experiments carried out with a a-Si:H thin film before (open circles) and after (black triangles) black etching. The principle of the experiment is illustrated in the inset. The lines are guides for the eye only.
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