Aluminium-doped zinc oxide (AZO) thin films with different aluminium (Al) concentrations were grown by RF-magnetron sputtering with substrate active cooling. Sputtering induced sample heating was aimed to be mitigated by the applied cooling, achieving films with electrical resistivities as low as , in the as-deposited state. Subsequently, an annealing treatment was performed to enhance the electrical properties and assess the effect of the Al concentration. The absorption coefficient spectra of zinc oxide (ZnO) exhibits an excitonic absorption contribution to the fundamental absorption that is typically not considered in AZO when determining the optical bandgap. Nevertheless, here we show that this free exciton band remains visible in AZO even at Al concentrations greater than 4 at.%. Additionally, the doping-induced defect states increases the width of tail states. These two factors have a substantial effect on the absorption edge, and thus must be considered with adequate models when attempting to determine the optical bandgap. In this work, we use a recently developed Elliot-based optical dispersion model to accurately determine the optical bandgap, exciton binding energy and Urbach energy of AZO thin films. On the other hand, we assess the infrared free carrier absorption, typically modeled by the Drude dispersion formula, by considering a complex frequency-dependent dynamical resistivity and the polar nature of the ZnO lattice…
Autor(es):LA Enrique, S Mishra, E Serquen, F Bravo, K Lizárraga, D Cespedes, M Piñeiro, P Llontop, JA Guerra
Año: 2025
Título de la revista: Journal of Physics D: Applied Physics
Volumen: 58
Número: 9
Url: https://doi.org/10.1088/1361-6463/ada168