DEVELOPMENT OF CONTROLLABLE CHEMICAL DEPOSITION TECHNIQUES FOR FABRICATION OF NANOCRYSTALLINE SEMICONDUCTING METAL SELENIDE THIN FILMS ― A POSSIBLE ROUTE TO CONTROL THE BAND-GAP ENERGY AND OTHER RELEVANT PARAMETERS OF SEMICONDUCTING NANOMATERIALS

摘要

Controllable chemical techniques for fabrication of nanocrystalline semiconducting metal selenide thin films are presented. The obtained thin films materials are identified using the method of X-ray diffraction. On the basis of recorded X-ray diffraction patterns, using Debye-Scherrer equation, the average crystal sizes of chemically deposited thin films are estimated. For investigation of their optical properties, UV-VIS spectra are recorded. Within the framework of parabolic approximation for the dependence of electronic energy on the wave vector, according to the Fermi's golden rule, the recorded optical spectra are correspondingly mathematically transformed. On the basis of dependence of (μhv)~(1) vs.hv the type of electronic transition is determined and the optical band gap energy (at room temperature) is calculated for each particular case. The calculated values of band gap energies for the investigated thin film materials are higher than the corresponding bulk values in those cases where these data are available. This finding is attributed to the size quantization effects. Since the crystal size is determined by deposition conditions, a possibility for controlling the band gap energies, as well as other relevant parameters of semiconducting thin films is outlined, which is of fundamental importance in nanoscience and nanotechnology of these materials.