Optical Band Gap Study of Bi1-xSbx (x = 0.10, 0.15 & 0.20) Thin Films

Authors C.F. Desai, P.H. Soni, M.P. Jani
Affiliations Department of Physics, Faculty of Science, The M.S. University of Baroda, Vadodara-390 002, India
Е-mail phsoni_msu@yahoo.com
Issue Volume 3, Year 2011, Number 1, Part 2
Dates Received 04 February 2011, in final form 30 April 2011, published online 08 May 2011
Citation C.F. Desai, P.H. Soni, M.P. Jani, J. Nano- Electron. Phys. 3 No1, 313 (2011)
PACS Number(s) 78.20.Ci, 81.15.Ef
Keywords Absorbance (2) , Band Gap (29) , Film thickness, Size effect (6) .
The solid-liquid interface of Bi1 – xSbx crystal growth is very favorable for investigations of electron- phonon phenomena. Bismuth is a semimetal with high electron and hole mobilities. When Bi is doped with Sb in the range of 7 to 22 atomic percentage, it undergoes semimetal-semiconductor transition. Interest in Bi-Sb materials system has recently been stimulated due to promise of a new generation of thermoelectric materials based on these alloys. The starting materials used in this study, Bi and Sb, were both of 99.999 % purity Bi1 – xSbx. Thin Films were grown using the thermal evaporation technique on a (001) face of NaCl crystal as a substrate at room temperature. The optical absorption was measured in the wave number range 500 cm – 1 to 4000 cm – 1. From the optical absorption data the band gap has been evaluated and the results indicate absorption through direct interband transition. The absorption spectra were obtained for films of various thicknesses. The band gap was found to increase with decreasing thickness, the dependence being inverse of square of thickness. The effect is most pronounced for thicknesses below 150 nm and is indicative of the quantum size effect. The estimate of the de Broglie wavelength of the carriers confirms this. The detailed results have been reported.

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