Analysis of thickness-dependent optical parameters of a-Si:H/nc-Si:H multilayer thin films
Tóm tắt
Multilayer thin films with alternate hydrogenated amorphous (a-Si:H) and nanocrystalline silicon (nc-Si:H) layers are deposited in hot wire chemical vapor deposition (HWCVD) chamber using hydrogen (H2) dilution of silane (SiH4). Two sets (two samples for each set) have different nc-Si:H layer thickness with the same a-Si:H thickness. The transmittance spectra, refractive index and absorption coefficient are obtained using UV–Vis spectroscopy. An analysis of Tauc plot suggests thickness-dependent optical band gap shift. The films with thick nc-Si:H layers show a decrease in band gap from 1.78 to 1.68 eV, whereas the films with lower nc-Si:H layer thickness have an increased band gap from 1.64 to 1.72 eV. Further, the slope of the Tauc plot (B) and disorder indicator (Urbach energy, E
u) show that the films with thick nc-Si:H layers are poorly ordered as hydrogen dilution increases. These results illustrate that band gap shift can be attributed to the crystal size effect and film disorder. This shifting of optical band gap with the nc-Si:H layer thickness is useful in tuning of the absorber layer band gap which finds an application in photovoltaics.
Tài liệu tham khảo
Gajovic, A., Gracin, D., Krunoslav, J.S., Ceh Parramon, M.: Correlating Raman spectroscopy and high resolution transmission electron microscopy studies of amorphous/nanocrystalline silicon thin films. Thin Solid Films 517, 5453–5458 (2009)
Staebler, D.L., Wronski, C.R.: Reversible conductivity changes in discharge-produced amorphous Si. Appl. Phys. Lett. 31, 292 (1977)
i-Cabarrocas, P.R.: Plasma enhanced chemical vapor deposition of amorphous, polymorphous and microcrystalline silicon films”. J. Non-Cryst. Solids 266–269, 31–37 (2000)
Saleh, R., Nickel, N.H.: Raman spectroscopy of B-doped microcrystalline silicon films. Thin Solid Films 427, 266 (2003)
Sai, H., Matsui, T., Koida, T., Matsubara, K., Kondo, M., Sugiyama, S., Katayama, H., Takeuchi, Y., Yoshida, I.: Triple-junction thin-film silicon solar cell fabricated on periodically textured substrate with a stabilized efficiency of 13.6%. Appl. Phys. Lett. 106, 213902 (2015)
Cashmore, J.S., Apolloni, M., Braga, A., Caglar, O., Cervetto, V., Fenner, Y., Aschemann, S.G., Goury, C., Hotzel, J.E., Iwahashi, T., Kalas, J., Kitamura, M., Klindworth, M., Kupich, M., Leu, G.F., Lin, J., Lindic, M.H., Losio, P.A., Mates, T., Matsunaga, D., Mereu, B., Nguyen, X.V., Psimoulis, I., Ristau, S., Roschek, T., Salabas, A., Salabas, E.L., Sinicco, I.: Record 12.34% stabilized conversion efficiency in a large area thin film silicon tandem (MICROMORPH™) module. Prog. Photovolta. Res. Appl. 23(11), 1441–1447 (2015)
Mavilla, N.R., Solanki, C.S., Vasi, J.: Raman spectroscopy of silicon-nanocrystals fabricated by inductively coupled plasma chemical vapor deposition. Phys. E 52, 59–64 (2013)
Panchal, A.K., Solanki, C.S.: Fabrication of silicon quantum dots in SiNx multilayer using hot-wire CVD. J. Cryst. Growth 311, 2659–2663 (2009)
Goh, B.T., Wah, C.K., Aspanut, Z., Rahman, S.A.: Structural and optical properties of nc-Si: H thin films deposited by layer by layer technique. Journal of Material Science: Mater Electron 25, 286–296 (2014)
Dalal, V.L., Madhavan, A.: Alternative designs for nanocrystalline silicon solar cells. J. Non-Cryst. Solids 354, 2403–2406 (2008)
Kar, D., Das, D.: Superior optical response of size-controlled silicon nano-crystals in a-Si:H/nc-Si: H superlattice films for multijunction solar cells. RSC Adv. 5, 61118–61126 (2015)
Tong, S., Liu, X., Bao, X.: Study of photoluminescence in nanocrystalline silicon/amorphous silicon multilayers. Appl. Phys. Lett. 66, 469–471 (1995)
Jun, K.H., Lim, K.S.: Enhanced vertical photo-sensitivity in & #x03BC;c-Si:H/a-Si: H superlattices. J. Non-Cryst. Solids 261, 268–272 (2000)
Pattnaik, S., Chakravarty, N., Biswas, R., Dalal, V., Slafer, D.: Nano-photonic and nano-plasmonic enhancements in thin film silicon solar cells. Sol. Energy Mater. Sol. Cells 129, 115–123 (2014)
Madhvan A., Dalal,, V.L., Noack M.A.: Superlattice structures for nanocrystalline silicon solar cell. In: IEEE International conference on Electro/Information Technology (EIT 2008) (2008), pp 383–388
Ganjoo, A., Golovchak, R.: Computer program PARAV for calculating optical constants of thin films and bulk materials: Case study of amorphous semiconductors. J. Optoelectron. Adv. Mater. 6, 1328–1332 (2008)
Tauc, J. (ed.): Amorphous and liquid semiconductor. Plenum Press, New York (1974)
Gracin, D., Aramon, J.S., Juraic, K., Gajovic, A., Ceh, M.: Analysis of amorphous nano crystalline multilayer structure by optical photo-deflection and photo-current spectroscopy. Micron 40, 56–60 (2009)
Rotaru, C., Nastase, S., Tomozeiu, N.: Amorphous phase influence on the optical bandgap of polysilicon. Phys. Status Solidi (A) 171, 365–370 (1999)
Hwang, H.S., Park, M.G., Ruh, H., Yu, H.: Investigations on microcrystalline silicon films for solar cell application. Bull. of Korean Chem. Soc. 31(10), 2909–2912 (2010)
Bakr, N.A., Mubarak, T.H., Habubi, N.F.: Impact of dilution gases on structure, properties and growth of hydrogenated nanocrystalline silicon (nc-Si:H) prepared by HW-CVD method. Int. J. Thin Film Sci. Technol. 2(2), 113–126 (2013)
Funde, A.M., Bakr, N.A., Kamble, D.K., Hawaldar, R.R., Amalnerkar, D.P., Jadkar, S.R.: Influence of hydrogen dilution on structural, electrical and optical properties of hydrogenated nanocrystalline silicon (nc-Si:H) thin films prepared by plasma enhanced chemical vapour deposition(PE-CVD). Solar Energy Material and Solar Cells 92, 1217–1223 (2008)
Goh, E.S.M., Chen, T.P., Sun, C.Q., Liu, Y.C.: Thickness effect on the band gap and optical properties of germanium thin films. J. Appl. Phys. 107, 024305 (2010)
Bhattacharya, K., Das, D.: Effect of deposition temperature on the growth of nanocrystalline silicon network from helium diluted silane plasma. J. Phys. D Appl. Phys. 41, 155420 (2008)
Tong, G.B., Aspanut, Z., Muhamad, M.R., Rahman, S.A.: Optical properties and crystallinity of hydrogenated nanocrystalline silicon (nc-Si:H) thin films deposited by rf-PECVD. Vacuum 86(8), 1195–1202 (2012)
Cody, G.D., Tiedje, T., Abeles, B., Brooks, B., Goldstein, Y.: Disorder and optical absorption edge of the hydrogenated amorphous silicon. Phys. Rev. Lett. 47(20), 1480–1483 (1981)
Street, R.A.: Hydrogenated amorphous silicon. Cambridge University Press, New York (1991). (ISBN: 0521371562)