Melioration of Electrical and Optical Properties of Al and B Co-Doped ZnO Transparent Semiconductor Thin Films

Abstract

Undoped, Al-doped and Al-B co-doped ZnO transparent semiconductor thin films were deposited on glass substrates by sol-gel method and spin coating technique. This study investigated the influence of Al (2 at.%) doping and Al (2 at.%)-B (1 or 2 at.%) co-doping on the microstructural, surface morphological, electrical and optical properties of the ZnO-based thin films. XRD analysis indicated that all as-prepared ZnO-based thin films were polycrystalline with a single-phase hexagonal wurtzite structure. The substitution of extrinsic dopants (Al or Al-B) into ZnO thin films can significantly degrade the crystallinity, refine the microstructures, improve surface flatness, enhance the optical transparency in the visible spectrum and lead to a shift in the absorption edge toward the short-wavelength direction. Experimental results showed that the Al-doped and Al-B co-doped ZnO thin films exhibited high average transmittance (>91.3%) and low average reflectance (<10%) in the visible region compared with the ZnO thin film. The optical parameters, including the optical bandgap, Urbach energy, extinction coefficient and refractive index, changed with the extrinsic doping level. Measured results of electrical properties revealed that the singly doped and co-doped samples exhibited higher electron concentrations and lower resistivities than those of the undoped sample and suggested that 2 at.% Al and 1 at.% B were the optimum dopant concentrations for achieving the best electrical properties in this study.

Effect of Al Incorporation on the Structural and Optical Properties of Sol–Gel AZO Thin Films

“…It is well known that by doping, the aforementioned properties of ZnO thin films can be significantly improved. For this purpose, the elements of II, III, IV groups are widely used, as they increase the electrical and optical performance of ZnO-based materials [24][25][26][27]. Among them, the group III elements such as B, Al, Ga and In are frequently used as extrinsic donors to achieve a higher conductivity, transparency and a better quality of the resulting doped films by promoting a free electron through the substitution of zinc cation with a trivalent ion [28,29].…”

Optical properties of ZnO nanorods and ZnO/CdZnS thin films

“…The optical properties of semiconductors are considered one of the most important properties of these materials because many electronic and optoelectronic applications depend on controlling these properties such as the absorption spectrum and the energy gap [13][14][15] . The process of surface modification and coating with other materials as surface layers is one of the most important methods and attempts to control the optical properties of semiconductor [16][17][18].…”