Important physical parameters of Bi₂O₃ thin films found by applying several models for optical data

Abstract

Different optical parameters for thin solid films can be computed as functions of wavelength from the optical transmission and reflection spectra. Subsequently, several models can be tested on the obtained data, in order to check their validity with respect to the materials under study. Moreover, these models offer the possibility to estimate essential physical parameters. Such models are tested within this article for the refraction index and for the real part of the complex dielectric constant, for bismuth trioxide thin films deposited on glass substrates maintained at three different temperatures. Also, the model proposed by Tauc is applied for the absorption spectrum of the same films, in order to determine the type of electronic transition and to estimate the optical energy bandgap. It will be noticed that the optical parameters vary rather significantly with changing substrate temperature, while the structure of the films, as studied by means of X-ray diffractometry is almost insensitive to this change of deposition parameter.

Bismuth Oxide Thin Films for Optoelectronic and Humidity Sensing Applications

“…8 Á 10 À5 Torr)o n t o chemically-cleaned microscope glass substrates (most commonly used, easily available, cheap and resistant to fairly high temperatures) kept at different temperatures, at least 50 degrees apart (e.g.27 C = room temperature, RT, 77 C and 127 C, respectively). Such deposition conditions would lead to bismuth trioxide films with a semi-transparent, dark gray appearance [11].…”

“…The optical data have to be processed in order to compute the most relevant optical parameters: the refractive index and the absorption coefficient. Then, different models can be applied to these parameters in order to infer new and important figures, such as the energy bandgap and type of electronic transitions within the films [11,[58][59][60][61].…”

“…Thus, as the XRD spectra from Figure 2 prove, merely Figure 1. XRD spectrum for a bismuth trioxide thin film [11]. Figure 2.…”

“…Bismuth trioxide thin films, Bi 2 O 3 , which is the most important industrial compound of bismuth, have also captured the interest of researchers because they have large energy bandgap, high refractive index, high photoconductivity, photosensitivity to ultraviolet radiation, etc. [1][2][3][4][5][6], properties that recommend bismuth trioxide for a wide variety of applications: optical coatings, solar cells, components in electronic circuitry, recording layers in CDs and DVDs and gas and humidity sensors [7][8][9][10][11][12][13]. Moreover, complex oxides containing Bi and V, such as BiVO 4 have been found as efficient photoelectrochemical (PEC) material for the treatment of polymer-containing wastewater from oilfields, especially when co-doped with W/Mo [14] or Zn [15] or by adding NaCl to the precursor solution when the chemical bath deposition method was employed for BiVO 4 photoanodes [16].…”

“…The deposition of bismuth trioxide can be accomplished by virtually any known method used for thin films: thermal evaporation [11,[20][21][22][23][24]; pulsed laser ablation-PLD [25][26][27][28][29][30], spray pyrolysis [31][32][33], electrodeposition [34], sol-gel [35], etc. Depending on the chosen deposition method, on its conditions (nature and temperature of the substrate, the vacuum level, the nature and pressure of the ambient gases, etc.)…”