Structural and optical properties of amorphous selenium prepared by plasma-enhanced CVD

Determination of Optical Properties of Undoped Amorphous Selenium (a-Se) Films by Dielectric Modeling of Their Normal-Incidence Transmittance Spectra

“…Therefore, in principle, two independent optical measurements are necessary at each spectral wavelength to solve for the unknowns and but, in practice, the true geometric thickness of the film is not known in prior and is thus to be determined at the same time-that is, three unknowns to be retrieved from two independent optical measurements at the same spectral wavelength, which demands adequate model suppositions or an otherwise optical analytical approach (Tan, 2006;Tan et al, 2007;Tan et al, 2006;Vautier et al, 1988;Bettstelleret al, 1993;Mulama et al, 2014;Benkhedir, 2006;Solieman et al, 2014;Adachi & Kao1980;Kotkata & Abdel-Wahab, 1990;Kotkata et al, 2009;Navarrete et al, 1990;Solieman & Abu-Sehly, 2010;Nagels et al, 1995;Tichy et al, 1996;Nagels et al, 1997;Tauc, 1972;Tauc, 1979;Heavens, 1991;Azzam & Bashara, 1987;Ward, 1994;Dragoman & Dragoman, 2002;Stenzel, 2005;Joo et al, 1999;Dobrowolski et al, 1983;Klein et al, 1990;Kukinyi et al, 1996;Chiao et al, 1995;Case, 1983;Peng & Desu, 1994;Birgin et al, 1999;Mulato et al, 2000;Erarslan & Gungor, 2010;Ventura et al, 2005;Manifacier et al, 1976;Swanepoel, 1983;Minkov, 1990;El-Naggar et al, 2009;…”

“…Regarding optical properties of undoped a-Se films, a lot of work were carried out for decades, but this issue is still continue to receive research attention as the existing information on their optical behavior is still less than adequate and disperse. The reported literature values of room-temperature band-gap energy of undoped or slightly-doped a-Se scatter greatly in the range (1.4 2.2 eV) and the values of their optical constants vary from one work to another (Mott & Davis, 1979;Tan, 2006;Tan et al, 2007;Tan et al, 2006;Vautier et al, 1988;Bettstelleret al, 1993;Adachi & Kao1980;Kotkata & Abdel-Wahab, 1990;Kotkata et al, 2009;Navarrete et al, 1990;Solieman & Abu-Sehly, 2010;Nagels et al, 1995;Tichy et al, 1996;Nagels et al, 1997;. The diversity of these findings may be related to different film thicknesses, to dissimilar methods and preparation conditions used in film deposition, and to variability of experimental techniques used to characterize optical response of studied films.…”

“…The diversity of these findings may be related to different film thicknesses, to dissimilar methods and preparation conditions used in film deposition, and to variability of experimental techniques used to characterize optical response of studied films. Discrepancies in reported optical properties of undoped a-Se films may also be linked to techniques employing different theoretical formulations for analyzing measured optical data, and to the interband transition mechanisms and band-energy structure models used for interpreting the optical absorption phenomena operative in them (Mott & Davis, 1979;Tan et al, 2006;Vautier et al, 1988;Bettstelleret al, 1993;Mulama et al, 2014;Benkhedir, 2006;Adachi & Kao1980;Kotkata & Abdel-Wahab, 1990;Kotkata et al, 2009;Navarrete et al, 1990;Solieman & Abu-Sehly, 2010;Nagels et al, 1995;Tichy et al, 1996;Nagels et al, 1997;.…”

“…The other spectral absorption regime is habitually assigned to the structural-disorder and defect-related low-absorption region below the absorption edge of amorphous (non-crystalline) dielectrics and semiconductors where , with the extinction coefficient is always debated to exhibit a linear-exponential dependence on the exciting photon energy and on the sample's ambient temperature , the so-called Urbach-tail behavior, of the analytical form given by (Mott & Davis, 1979;Nagels et al, 1995;Tichy et al, 1996;Nagels et al, 1997) ,…”

“…The parameters and are different constants of the amorphous material, is an energy constant comparable to , and Γ is a temperature-dependent energy parameter that signifies the extent of energy states below absorption edge, referred to as the breadth of absorption (Urbach-) tail, neither its origin nor temperature dependency is a definitely solved problem, with a variety of formulations for its variation with temperature (Nagels et al, 1995;Tichy et al, 1996;Nagels et al, 1997). To limit the Tauc -model to the interband spectral region of an amorphous semiconductor and to make mathematical evaluation of the respective real part of its complex dielectric constant feasible and physically meaningful, a phenomenological broadening term Γ has been added to the photon energy , in addition to multiplying the -formulation given in Equation (19) by step functions of the Heaviside type to account for cutoff energies at the absorption edge and high-energy side (Adachi, 1991).…”