Optical and Structural Properties of Bismuth Doped ZnO Thin Films by Sol-Gel Method: Urbach Rule as a Function of Crystal Defects

E.F. Keskenlera, S. Aydınb, G. Turgutb and S. Doğanc aRecep Tayyip Erdoğan University, Faculty of Engineering, Department of Nanotechnology Engineering, Rize, 53100, Turkey bAtatürk University, K. Karabekir Education Faculty, Department of Physics, Erzurum, 25240, Turkey cDepartment of Electrical and Electronics Engineering, Faculty of Engineering and Architecture, Balikesir University, Balikesir, 10145, Turkey

Received: October 3, 2012; Revised version: April 25, 2014; In final form: June 26, 2014

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Bismuth (Bi) doped zinc oxide (ZnO:Bi) thin films were prepared on glass substrates by sol-gel spin coating technique using homogeneous precursor solutions, and effects of Bi doping on the structural and optical properties of ZnO were investigated. The crystalline of ZnO films shifted from polycrystalline nature to amorphous nature with Bi doping. The plane stresses (σ) for hexagonal ZnO and ZnO:Bi crystals were calculated according to the biaxial strain model. The Urbach rule was studied as a function of non-thermal component to the disorder (defects in crystal structures) which is especially observed in the case of non-crystal semiconductors. The calculated Urbach energies and steepness parameters of undoped ZnO and ZnO:Bi films varied between 44.33 meV and 442.67 meV, and 58.3 × 10-2 and 5.8 × 10-2, respectively. The Urbach energies of the films increased with an increase in the Bi doping concentration and a great difference was observed for 7.0 mol.% doping. The band gap values of the films exhibited a fluctuated behavior as a result of doping effect.

DOI: 10.12693/APhysPolA.126.782 PACS numbers: 78.20.-e, 78.66.Hf, 78.40.Fy, 78.66.Jg, 68.37.Yz, 68.55.ag, 68.60.Bs