Structural optical and electrical properties of transparent conductive ITO/Al-Ag/ITO multilayer contact

Developing a new design and structure of transparent conductive oxides (TCO) materials to improve performance in optoelectronic devices are important and quite challenging. Microstructural, optical and electrical properties of sandwiched Al-Ag metals interlayer between top and bottom ITO layers (ITO/Al-Ag/ITO) have been investigated. The multilayer ITO/Al-Ag/ITO (IAAI) films were prepared using RF and DC magnetron sputtering method. Post annealing treatment at 400oC was conducted on IAAI and ITO (for reference) films in air. X-ray diffraction measurements show that the insertion of Al-Ag intermediate bilayer led to the crystallization of Ag interlayer even at as-deposited stage. Peaks intensities at ITO (222), Ag (111) and Al (200) crystal plane were observed after annealing treatment, indicating an enhancement in crystallinity of the IAAI film. The post-annealed IAAI film reveals a continuous and smooth surface roughness with improved growth in grain size as examined by atomic force microscopy (AFM) and field emission scanning electron microscopic (FESEM) respectively. Comparing the optoelectronic properties of IAAI film with single ITO film, the annealed IAAI film exhibited a remarkable improvement in optical transmittance (86.1%) with a very low sheet resistance of 2.93 Ω/sq as measured by UV-Vis spectrophotometer and four-point probe method. The carrier concentration increased more than double when Al-Ag layer was inserted between the ITO layers as determined by Hall Effect measurements. The under layer Al film helps to halts the Ag film agglomeration and oxidation which subsequently enhances the stability of IAAI multilayer film.  The performance of IAAI contact has been found to be high at 76.4 × 10-3 Ω compares to single ITO (69.4 × 10-3) contact as calculated by the figure of merit (FOM).