Physical properties and heterojunction device demonstration of aluminum-doped ZnO thin films synthesized at room ambient via sol–gel method

• Published in: Journal of alloys and compounds Vol. 521; pp. 155 - 162
• Main Authors: Karaagac, Hakan, Yengel, Emre, Saif Islam, M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 25.04.2012; Elsevier
• Subjects: Alloys; Aluminum; Azo; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Exact sciences and technology; Ii-vi semiconductors; Low-field transport and mobility; piezoresistance; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Oxide materials; Physics; Semiconductors; Silicon substrates; Sol gel process; Thin films; X-ray diffraction; Zinc oxide; Thin films; X-ray diffraction; Sol–gel process; Oxide materials; Transparency; Electrical conductivity; Surface morphology; XRD; Aluminium Zinc Oxides Mixed; Energy gap; Chemical composition; Silicon; Wide band gap semiconductors; IV characteristic; Sol-gel process; Optical constants; Heterostructures; Piezoresistance
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2012.01.103

► Undoped and Al doped ZnO (AZO) thin films were successfully prepared using sol–gel technique. ► Structural analysis has revealed that Al doping has a significant influence on preferential orientation. ► It has been observed that wrinkles forms on the surface of films when annealed with a fast heat ramp up rate. ► Optical analysis has revealed that that the band gap energy of ZnO thin film increases with increasing Al doping concentration. ► The lowest resistivity is observed for 1% Al ZnO thin film, which is 2.2×10−2(Ωcm). ZnO and some of its ternary wide-bandgap alloys offer interesting opportunities for designing materials with tunable band gaps, strong piezoresistivity and controlled electrical conductance with high optical transparency. Synthesizing these materials on arbitrary substrates using low-cost and unconventional techniques can help in integrating semiconductors with different physical, electrical, and optical characteristics on a single substrate for heterogeneous integration of multifunctional devices. Here we report the successful synthesis of aluminum (Al) doped ZnO (AZO) thin films on soda-lime glass, silicon and fluorine doped tin oxide (FTO) pre-coated glass substrates by using sol–gel deposition method at ambient condition. X-ray diffraction (XRD) analysis revealed that varying degree of Al doping significantly impacts the crystal orientation, semiconductor bandgap and optical transparency of the film. Crystal structure of the film is also found to be strongly correlated to the characteristics of the substrate material. The impact of heating rate during post annealing process is studied and optimized in order to improve the surface morphology of the deposited films. Optical characterizations have revealed that bandgap energy of AZO films can be tuned between 3.30eV and 4.1eV as the Al concentration is varied from 1% to 20%. Similarly, electrical characteristics of these films indicate that 1% AZO film has the lowest resistivity of 2.2×10−2Ωcm. Finally, 1% Al doped AZO thin film was used in fabricating a p-Si/n-AZO heterojunction, which exhibited good diode characteristics with more than five orders of magnitude rectification ratio and an ideality factor of 3.28.