Impact of Thickness on the Optical Properties of Selenium Thin Films

Abstract

Objectives: The primary objective of this investigation is to make a systematic study on the impact of thickness on optical properties, such as energy gap, absorption coefficient, optical density etc., for selenium thin films. Understanding of the band gap energy and its influence on film thickness is of utmost importance in acquiring the intended electrical characterization of semiconducting films. Materials and methods: Ultra-purity selenium (99.99 %) was deposited on glass substrates. During deposition, the glass substrate with its holder were rotated with constant speed to have a smooth coating. Results and discussions: The XRD findings indicate that selenium is amorphous in nature. The optical band gap energy is found to be decreasing form (2.3 to 2eV) with the rise of film thickness in interval (200 to 1000 nm). The band gap energy obeys inverse square law with respect to thickness. Conclusion: We have properly grown thin films of Se below the De Broglie wavelength limit by thermal evaporation in vacuum. The optical density varies directly with film thickness. The absorption coefficients were in the interval (0.5 to 4) × 107m-1. The AFM results confirmed that the Se nano-size increases with the increase in thickness. Both the grain boundaries and sub-grain regions are clearly visible in the SEM micrographs