“…From the transmittance spectra, the optical bandgap of the grown structure can be calculated by using the following Tauc expression (Jakkala and Kordesch, 2017): where a , hv , A , E g and n are absorption coefficient, Planck’s equation (photon energy), a constant value that depends on transition probability, optical energy gap and a value that depend on the nature transition of electron (direct allowed semiconductor; n = 1/2), respectively. The absorption coefficient of the structure can be calculated by using the following Beer–Lambert law relation (Yusof et al , 2018): where T , I i , I e , a and d are transmittance, incident light, transmitted light, absorption coefficient and thickness of the structure, respectively.…”