Band gap dependence upon thickness of chalcogenide Ge-As-S thin films

We have studied thin films of Ge25As30S45 glass evaporated by electron-beam technique. We have analyzed the transmission spectra of thin films of the same nominal composition, obtained under identical conditions, but with four different thicknesses varying from 1 to 7 micrometers. All fabricated films were annealed for 1h at 300oC (below the glass transition temperature of this glass). As a result, we observed a thickness dependent blue-shift of about 100 nm of their transmission edge. We have calculated the optical band gap of those annealed thin films and we have observed that the slope of absorption edge becomes less abrupt and the band gap decreases when their thickness increases. Furthermore, this band gap decrease is accompanied with a broadening of the tails and localized states, which indicates an increase of the degree of disorder in the vitreous network. This could be explained by the higher density of defects and dangling bonds in the thinner films since the amount of deposited material is smaller. This implies therefore an increase of both the degree of disorder and the concentration of defects, and consequently the decrease of the optical gap.

[1]  Ashtosh Ganjoo,et al.  CURRENT UNDERSTANDING OF PHOTOINDUCED VOLUME AND BANDGAP CHANGES IN AMORPHOUS CHALCOGENIDES , 2001 .

[2]  Virginie Nazabal,et al.  Dysprosium doped amorphous chalcogenide films prepared by pulsed laser deposition , 2006 .

[3]  Younes Messaddeq,et al.  Study of photoinduced birefringence vs As content in thin GeAsS films , 2013 .

[4]  K. L. Chopra,et al.  Photoinduced changes in the Urbach tail in Ge‐ and As‐based chalcogenide glasses , 1983 .

[5]  M. Fadel,et al.  Some optical properties of Se-Ge-As amorphous chalcogenide glasses , 1992 .

[6]  N. Mott,et al.  Electronic Processes In Non-Crystalline Materials , 1940 .

[7]  Ashtosh Ganjoo,et al.  Photoinduced structural changes in obliquely deposited As- and Ge-based amorphous chalcogenides: correlation between changes in thickness and band gap , 1998 .

[8]  S. Elliott,et al.  The Physics and Chemistry of Solids , 1956, Nature.

[9]  A. A. Abu-Sehly,et al.  Effect of annealing temperature on the optical and electrical properties of amorphous As45.2Te46.6In8.2 thin films , 2002 .

[10]  重治 小野木,et al.  Journal of Applied physics,Vol.33 : 1962年に発表されたレオロジー関連の論文 , 1963 .

[11]  Annie Pradel,et al.  CHALCOGENIDE THIN FILMS DEPOSITED BY RADIO-FREQUENCY SPUTTERING , 2004 .

[12]  J. Gonzalez-Leal,et al.  On the irreversible photo-bleaching phenomenon in obliquely-evaporated GeS2 glass films , 1997 .

[13]  G. Amin,et al.  Structure, optical absorption and electrical conductivity of amorphous AsSeGe thin films , 2001 .

[14]  M. Wakkad,et al.  Optical and calorimetric studies of Ge-Sb-Se glasses , 2000 .

[15]  L. Ambrosio,et al.  Journal of materials science: materials in medicine. , 2003, Journal of materials science. Materials in medicine.

[16]  V. Pamukchieva,et al.  Photoinduced anisotropy in photobleached Ge–As–S films , 2001 .

[17]  M. Abdel-Rahim,et al.  Annealing dependence of optical and electrical properties of Ga8As46Te46 thin films , 1999 .

[18]  M. Abdel-Rahim,et al.  Optical absorption and electrical conductivity of amorphous AsTeGe thin films , 1998 .