The effect of thickness and/or doping on the nonlinear and saturable absorption behaviors in amorphous GaSe thin films

Kurum U., Yuksek M., YAĞLIOĞLU H. G., ELMALI A., Ates A., KARABULUT M., ...Daha Fazla

JOURNAL OF APPLIED PHYSICS, cilt.108, sa.6, 2010 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 108 Sayı: 6
  • Basım Tarihi: 2010
  • Doi Numarası: 10.1063/1.3486047
  • Dergi Adı: JOURNAL OF APPLIED PHYSICS
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Anahtar Kelimeler: absorption coefficients, amorphous semiconductors, defect states, gallium compounds, III-VI semiconductors, optical saturable absorption, semiconductor doping, semiconductor thin films, 2-PHOTON ABSORPTION, OPTICAL-PROPERTIES
  • Ankara Üniversitesi Adresli: Evet

Özet

We investigated the nonlinear and saturable absorption characteristics of very thin amorphous undoped GaSe, Ge (0.01 at. %), and Sn (0.5 at. %) doped GaSe films by pump-probe and open aperture Z-scan techniques. Linear absorption measurements indicate blueshift in energy with increasing film thickness. Thinner films exhibit saturable absorption while thicker films exhibit nonlinear absorption for 4 ns and 65 ps pulse durations. The films exhibit competing effects between nonlinear and saturable absorption. Saturable absorption behavior weakens while nonlinear absorption appears with increasing film thickness. In addition to that, saturable absorption behavior is very sensitive to doping. Doping causes absorption behaviors to appear in thinner films compared to undoped films. These behaviors are attributed to increasing localized defect states with increasing film thickness and doping. To derive the transmission in open aperture Z-scan data, a theoretical model incorporating one photon, two photon, and free carrier absorptions and their saturations were considered. The experimental curves were fitted to the theory of open aperture Gaussian beam Z-scan based on the Adomian decomposition method. Nonlinear absorption coefficients and saturation intensity thresholds were extracted from the fitting of the experimental results for both pulse durations used for the experiments. Saturation intensity threshold values increased with increasing film thickness and doping. The lowest saturation intensity threshold for undoped GaSe film was found to be 1.9 X 10(-3) GW/cm(2) for 45 nm film thickness and increased about two orders of magnitude for 74 nm film thickness. (C)2010 American Institute of Physics. [doi:10.1063/1.3486047]