Pulsed laser deposited Al-doped ZnO thin films for optical applications

Highly transparent and conducting Al-doped ZnO (Al:ZnO) thin films were grown on glass substrates using pulsed laser deposition technique. The profound effect of film thickness on the structural, optical and electrical properties of Al:ZnO thin films was observed. The X-ray diffraction depicts c-axis, plane (002) oriented thin films with hexagonal wurtzite crystal structure. Al-doping in ZnO introduces a compressive stress in the films which increase with the film thickness. AFM images reveal the columnar grain formation with low surface roughness. The versatile optical properties of Al:ZnO thin films are important for applications such as transparent electromagnetic interference (EMI) shielding materials and solar cells. The obtained optical band gap (3.2–3.08 eV) was found to be less than pure ZnO (3.37 eV) films. The lowering in the band gap in Al:ZnO thin films could be attributed to band edge bending phenomena. The photoluminescence spectra gives sharp visible emission peaks, enables Al:ZnO thin films for light emitting devices (LEDs) applications. The current–voltage (I–V) measurements show the ohmic behavior of the films with resistivity (ρ)~10−3 Ω cm.