| Al-doped ZnO (Al: ZnO) belongs to a class of materials known as transparent conductors with remarkable combination of high electrical conductivity and good optical transparency. Such a blend of properties allows them to be used for many optoelectronic devices, light emitting diodes, solar cells, etc. However, recent observations of metal-like and metal-semiconducting transitions in this system reveal a lack of understanding of the fundamental scattering processes that lead to such behaviors.;In this work, we have investigated the effect of Al-doping on the structural, morphological, electrical and optical properties of ZnO thin films. Al-doped ZnO films were deposited using RF-magnetron sputtering, where the Al-content was varied from 1 to 10 at%. No noticeable traces of secondary phases were detected as seen from the X-ray diffraction measurements. The electrical resistivity decreased by greater than two orders, an effect of Al-doping. Metal-like behaviors were observed due to the high degeneracy of the samples. Metal-semiconducting transitions were observed, which were attributed to charge disorder, explained using weak localization theory. The evidence of weak localization was justified from the observation of negative magnetoresistance at all doping levels. Magnetoresistance analysis clearly shows that both electron-electron and electron-phonon are the dominant inelastic scattering mechanisms that control the conductivity behaviors and lead to the observed metal-semiconducting transitions.;The optical absorption edge shows a blue shift with Al-doping attributed to the Burstein-Moss theory of band filling. The results have been explained considering the non-parabolic nature of the conduction and valence bands. The non-parabolic nature of the bands was confirmed from the plasma edge analysis as well where the variation of the effective mass with increasing carrier concentration should be accounted for at heavy doping and plays a dominant role in Al-doped ZnO system.;The primary objective of this work was to understand the underlying scattering processes that occur through detailed magneto-transport studies. In addition, the effect of heavy doping as seen from the optical studies such as absorption edge and plasma edge is also presented. |
