Abstract:

Experimentally:

The amorphous Selenium thin films were prepared for different thicknesses using thermal evaporation method on a glass substance at the room temperature and at pressure of 1.0 atm. The purpose of the research is to determine the energy gap for the gray Selenium using two different methods, which are spectrophotometer, and I-V measurement. The band gap of thin films with respect to normal to vapor beam detection decreases with the angle of deposition. In our case, the experimental band gap using spectrophotometer is 1.9 eV, while the theoretical value is 1.7 eV.

In the research, we found out the variety of elements at the surface as well as the nature of thin film and the structure of the Selenium thin film using two ways, scanning electron microscope (SEM), and X-RAY. Scanning electron microscope helps to observe the optical properties of Selenium when the substrate is heated and unheated. As a result, some elements were found such as Oxygen. In addition, because of grains that formed on the thin film, the Selenium is an amorphous. Also, X-RAY provides to find out the diffraction pattern of the structure of the Selenium thin film.

Theoretically:

In this part of research, we used WEIN2K package to find out the electrical properties of Selenium, and the energy gap. To calculate the energy gap, WIEN2K provides two methods. The first method is the density of state (DOS), and the second method is the band structure. The experimental lattice constants for Selenium are a= 4.64 Angstrom, b= 4.64 Angstrom, c= 4.9495 Angstrom, and since the structure is hexagonal, then α=β=90 and γ=120. The Selenium structure contains three Selenium atoms with positions 0.2037a, 0.0b, 0.0c for atom one, and for the second atom are 0.7963a, 0.7963b, 0.3333c and 0.0a, 0.2037b, 0.6667c for the third atom. As a result, we obtain that the energy gap is 1.3 eV using DOS and Generalized Gradient Approximation 2008 (GGA 08). From the band structure, it is quite obvious to identify weather the band gap is direct or indirect. The optical energy band gap of the thin film decreases with the thickness due to quantum size effect. Moreover, we implement Modified Becke Johnson method (MBJ) to get more precise results, and we conclude that the energy gap of hexagonal Selenium is 1.3 eV.

Hossam AlDeen Yousef

Affiliation

Refine Results

Photoelectric properties of Selenium