Gerke, S.; Becker, H.-W.; Rogalla, D.; Singer, F.; Brinkmann, N.; Fritz, S.; Hammud, A.; Keller, P.; Skorka, D.; Sommer, D.; Weiß, C.; Flege, S.; Hahn, G.; Job, R.; Terheiden, B.
Influence of post-hydrogenation upon electrical, optical and structural properties of hydrogen-less sputter-deposited amorphous silicon
Teil von
  • Thin solid films, 2016-01-01, Vol.598, p.161-169
Ort / Verlag
LAUSANNE: Elsevier
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Amorphous silicon (a-Si) is common in the production of technical devices and can be deposited by several techniques. In this study intrinsic and doped, hydrogen-less amorphous silicon films are RF magnetron sputter deposited and post-hydrogenated in a remote hydrogen plasma reactor at a temperature of 370 °C. Secondary ion mass spectrometry of a boron doped (p) a-Si layer shows that the concentration of dopants in the sputtered layer becomes the same as present in the sputter-target. Improved surface passivation of phosphorous doped 5 Ω cm, FZ, (n) c-Si can be achieved by post-hydrogenation yielding aminority carrier lifetime of ∼360 μs finding an optimum for ∼40 nm thin films, deposited at 325 °C. This relatively low minority carrier lifetime indicates high disorder of the hydrogen-less sputter deposited amorphous network. Post-hydrogenation leads to a decrease of the number of localized states within the band gap. Optical band gaps (Taucs gab as well as E ) can be determined to ∼1.88 eV after post-hydrogenation. High resolution transmission electron microscopy and optical Raman investigations show that the sputtered layers are amorphous and stay like this during post-hydrogenation. As a consequence of the missing hydrogen during deposition, sputtered a-Si forms a rough surface compared to CVD a-Si. Atomic force microscopy points out that the roughness decreases by up to 25% during post-hydrogenation. Nuclear resonant reaction analysis permits the investigation of hydrogen depth profiles and allows determining the diffusion coefficients of several post-hydrogenated samples from of a model developed within this work. A dependency of diffusion coefficients on the duration of posthydrogenation indicates trapping diffusion as the main diffusion mechanism. Additional Fourier transform infrared spectroscopy measurements show that hardly any interstitial hydrogen exists in the posthydrogenated a-Si layers. The results of this study open the way for further hydrogen diffusion experiments which require an initially unhydrogenated drain layer.
ISSN: 0040-6090
ISSN: 1879-2731
DOI: 10.1016/j.tsf.2015.11.063

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