In this study, Ge-rich a-SiGe films have been fabricated by RF magnetron co-sputtering at two different base-pressures. As-sputtered SiGe thin-films were then brought to ex-situ thermal annealing process at 550 ᵒ C. The result from transmittance was reduced owing to lesser defect density. Tauc’s model was used to measure the bandgap and it was found that the exponent n has a direct relation with atomic density and for low density of SiGe thin-film exponent n of 5 is the closest value comparable to the assumption. Introduction S. A. Shahahmadi 1, Ahmad A Zulkefle 1, Maslan Zainon 1, Nilofar Asim 1, Kamaruzzaman Sopian 1, Nowshad Amin 1,2,3 1 Solar Energy Research Institute, The National University of Malaysia, Bangi, Selangor, Malaysia 2 Department of Electrical, Electronic and System Engineering, Faculty of Engineering and Built Environment, The National University of Malaysia, Bangi, Selangor, Malaysia 3 Advanced Materials Research Chair, Chemistry Department, College of Sciences, King Saud University, Riyadh 11451, Saudi Arabia * Optical Properties of a-SiGe Thin Films on Glass by Co-Sputtering for Photovoltaic Application Hydrogenated amorphous silicon-germanium (a-SiGe:H) has been widely used at the bottom cell of thin-film silicon-based tandem structures. Tandem solar cells are usually fabricated by applying a-SiGe:H with a tunable band gap in the range of eV. However, hydrogen has an unstable host lattice due to the thermal annealing and poor endurance under high illumination. These characteristics of SiGe:H films have shown large scale of potential, which might be beneficial for non-hydrogenated SiGe thin-films. In order to deposit non-hydrogenated SiGe, sputtering is an alternative approach without involving any toxic gases. This inexpensive deposition technique can be applied in a large scale area. However, a few number of researches have been explored about deposition of SiGe through sputtering technique while the properties of SiGe have not been well documented at present. In this study, we have investigated the optical properties of amorphous silicon germanium (a-SiGe) thin-films under different atomic densities grown by sputtering. We have changed the atomic density based on defect passivation by ex situ thermal annealing process beside sputtering base-pressure.  All films are entirely amorphous in nature.  Sample 1 due to high surface roughness and defects density has the highest transmittance in this study, whereas sample 2 has lower transmittance.  By ex situ thermal annealing, transmittance reduces in sample 1 after thermal annealing (sample 3), despite the fact that transmittance spectra does not show any significant changes in sample 2 after thermal annealing (sample 4).  The highest α could be observed in sample 3 and 4. Notably, sample 3 has lesser α in value compared with sample 1 due to lesser defects.  The trend of bandgaps value in all of the graphs are same and bandgap reduction occurs by improving structural quality of i-a-Si 25 Ge 75 thin-films.  We have chosen 5 as a value of exponent n concerning the atomic density of thin-films. Therefore, sample 4 with the bandgap of 1.07 eV has the lowest defect density and sample 2, sample 3 and sample 1 have got the next titles respectively. Major Findings and Discussions Conclusion Experimental Procedures ENGE 2014 – International Conference on Electronic Materials and Nanotechnology for Green Environment The absorption coefficient and the transmittance spectra: (a) Transmittance (b) Absorption coefficient. Substrate Cleaning Process Methanol, acetone, methanol, DI water sonification for 10 minutes in each solvent Substrate Cleaning Process Methanol, acetone, methanol, DI water sonification for 10 minutes in each solvent Co-Sputtered SiGe Film Base pressure = Torr Argon Flow = 3 SCCM i-Si Power = 25 W i-Ge Power = 30 W Sub. Temperature = RT Si 0.25 Ge 0.75 Thickness = 650 nm Co-Sputtered SiGe Film Base pressure = Torr Argon Flow = 3 SCCM i-Si Power = 25 W i-Ge Power = 30 W Sub. Temperature = RT Si 0.25 Ge 0.75 Thickness = 650 nm Thermal Annealed SiGe Film Base Pressure = 20 mTorr Nigtrogen Flow = 20 mL/min Annealing Time = 300 min Annealing Temp. : 550 ˚C Natural cooling to RT Thermal Annealed SiGe Film Base Pressure = 20 mTorr Nigtrogen Flow = 20 mL/min Annealing Time = 300 min Annealing Temp. : 550 ˚C Natural cooling to RT The Tauc’s plots of samples with different exponent n. (a) n=2,(b) n=3, (c) n=4 and (d) n=5. (e) The overall bandgaps Sputter base- pressure Annealing temperature Sample 14 × TorrNon-annealed Sample 24 × TorrNon-annealed Sample 34 × Torr 550 ᵒ C Sample 44 × Torr 550 ᵒ C