Effect of aluminum addition on the optical, morphology and electrical behavior of spin coated zinc oxide thin films

Aluminum-doped ZnO thin films of high optical transmittance (∼ 84-100%) and low resistivity (∼ 2.3x10-2 Ωcm) have been prepared on glass substrate by the spin coating and subsequent annealing at 500°C for 1h in air or vacuum. Effect of aluminum doping and annealing environment on morphology, optical transmittance and electrical resistivity of ZnO thin films has been studied with possible application as a transparent electrode in photovoltaic. The changes occurring due to aluminum addition include reduction in grain size, root mean square roughness, peak-valley separation, and sheet resistance with improvement in the optical transmittance to 84-100% in the visible range. The origin of low electrical resistivity lies in increase in i) electron concentration following aluminum doping (being trivalent), formation of oxygen vacancies due to vacuum annealing, filling of cation site with additional zinc at solution stage itself and ii) carrier mobility.