Optical properties of hydrogenated amorphous carbon determined by ellipsometry

Margit Koos; Tivadar Lohner; Said H. Moustafa; Istvan Pocsik

doi:10.1117/12.320958

19 August 1998 Optical properties of hydrogenated amorphous carbon determined by ellipsometry

Margit Koos, Tivadar Lohner, Said H. Moustafa, Istvan Pocsik

Proceedings Volume 3573, OPTIKA '98: 5th Congress on Modern Optics; (1998) https://doi.org/10.1117/12.320958
Event: OPTIKA '98: Fifth Congress on Modern Optics, 1998, Budapest, Hungary

Abstract

The complex dielectric function [(epsilon) ((omega) ) equals (epsilon) ₁((omega) ) + i(epsilon) ₂((omega) )] and the complex refractive index [N((omega) ) equals n((omega) ) + ik((omega) )] are presented for diamond-like amorphous carbonlayers as well as for amorphous carbon thin films (a- C:H) exhibiting other properties. By employing spectral ellipsometry the optical constants were determined in the photon energy range of 1.47 - 4.59 eV. Series of thin films were prepared in radio frequency plasma discharge of methane by varying the negative self bias (U_S.b.) in the range of 200 V < U_S.b. < 600 V. The a-C:H samples in this series exhibit transition in electrical and optical properties with increasing room temperature conductivity from approximately 4 X 10^-10 (Omega) ^-1 cm^-1 to 2 X 10^-2 (Omega) ^-1 cm^-1 and with decreasing optical gap from 1.3 eV to 0.5 eV as the deposition voltage changes in the range of 200 - 600 eV. The most pronounced changes in optical constants and in bonding structure occur near 500 V self bias. The (epsilon) ₂((omega) ) spectrum exhibits a broad maximum which shifts to lower energies by increasing deposition self bias. The optical properties are discussed in terms of electronic band structure related to sp³ and sp² hybridized bonding states of carbon atoms and to intermediate range ordering of sp² bonded sites.

Citation Download Citation

Margit Koos, Tivadar Lohner, Said H. Moustafa, and Istvan Pocsik "Optical properties of hydrogenated amorphous carbon determined by ellipsometry", Proc. SPIE 3573, OPTIKA '98: 5th Congress on Modern Optics, (19 August 1998); https://doi.org/10.1117/12.320958

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