Abstract:
Transparent conductive oxides (TCOs) are a unique class of materials which exhibit appreciable level of electrical conductivity, high optical transparency in the visible range and high infrared reflectivity in a single material. Their uniqueness has demonstrated to be of great importance to many optoelectronic applications. However, compared to the prosperous n-type TCOs, the synthesis, performance and development of existing p-type TCOs has impeded the advancement in technology based on their applications. This comes about from their unique electronic configuration which makes the VBM localized and anisotropic in nature. To address this challenge, Tin have been predicted to demonstrate promising results when doped with group (III) atoms with Sb-co-doping enhancing stability of films. In this study, p-type SnO2:Ga and Sb-co-doped SnO2:Ga thin films have been successfully prepared on blue plus microscope glass substrates using the sol-gel dip-coating method. The concentrations of gallium and antimony composition have been varied and their effects investigated. The transmittance spectra of undoped SnO2 film is transparent with an average transmittance ranging between 61.1 - 81.1 %, SnO2:Ga films at 50.4 – 72.6 % and Sb-co-doped SnO2:Ga films at 53.6 - 78.1 % when set at a wavelength range of 400 nm to 900 nm respectively. Undoped SnO2 has a direct band gap value of 3.89 eV, SnO2:Ga films at values of between 4.07 eV - 4.15 eV and Sb-co doped SnO2:Ga films at 4.10 eV - 4.16 eV. Optical band gap widening and the narrowing is observed for all SnO2:Ga and Sb-co-doped SnO2:Ga. On the conductivity types, all the prepared films are p-type conductive except at higher co-doping levels of Sb. SnO2:Ga thin films resistivity is of order 1.6 x 10-2 to 3.44 x 10-3 Ω cm and Sb-co-doped SnO2:Ga order 4.55 x 10-3 to 6.92 x 10-3 Ω cm. I-V characteristics demonstrate an ohmic behaviour for all films. Morphological analysis reveals films exhibiting smooth surfaces, devoid of cracks. Average crystallite sizes and FWHM values defines a better crystallinity of the films. Combinations of these properties in a single film contribute a valuable insight into p-type TCOs of SnO2:Ga and Sb-co-doped SnO2:Ga films, addressing the limitations associated with their characterization and suitable for optoelectronic applications.
