Origin of enhanced carrier mobility and electrical conductivity in seed-layer assisted sputtered grown Al doped ZnO thin films

In the present study, a ZnO seed-layer assisted sputtered deposition approach is used to enhance the carrier mobility and electrical conductivity of Al doped ZnO (AZO) thin film. The seed layer assisted grown AZO thin film showed an electrical conductivity, optical transmittance, and high figure-of-merit of 1806.94 ± 10.50 S/cm, >90% (Vis-NIR), and 1.68 × 10⁻² Ω⁻¹, respectively. This high optoelctronic properties make AZO thin film qualified to be used for transparent electrode applications. The carrier mobility in the seed-layer assisted grown AZO thin film is observed to be 15.21 ± 0.04 cm²/Vs which is two-fold higher than AZO thin film grown without seed-layer. The origin of enhanced carrier mobility is investigated in the light of generated defects and their nanoscale distribution in the polycrystalline AZO thin film during the sputtering process. The low grain boundary potential is observed in seed layer assisted grown AZO thin film using nanoscale Kelvin probe force microscopy and was attributed to the low defects segregation towards grain boundaries. The argument of low carrier defects like zinc interstitial and oxygen vacancies in seed-layer assisted grown AZO thin film is experimentally verified using X-ray photoelectron spectroscopy analysis. The analysis of defect chemistry and their nanoscale distribution helps us to understand that intrinsic defects and their segregation at grain boundaries critically affect the carrier mobility in AZO thin film.