Relation between synthesis conditions, dopant position and charge carriers in aluminium-doped ZnO nanoparticles

Abstract

The ability to achieve an understanding of the correlations between chemical synthesis, doping mechanism and properties of aluminium-doped zinc oxide (ZnO:Al) nanocrystals is of great importance to evaluate the potential of ZnO:Al nanocrystals as optimal building blocks for solution deposited transparent conductive oxide layers. Two series of Al-doped ZnO nanoparticles were synthesized by solution-based methods under different conditions yielding phase-pure wurtzite ZnO:Al nanocrystals with different morphologies (quasispheres and rods). In both series 80% of the input Al is incorporated in the ZnO:Al crystals. Furthermore, ²⁷Al nuclear magnetic resonance demonstrated a 5 times higher tetrahedral Al content for the quasispheres, which can be directly linked to the presence of free charge carriers, as showed with Fourier transform infrared spectroscopy. XPS data show the Zn²⁺ and O²⁻ chemical state of the constituting ions. It is demonstrated that an efficient Al doping, creating charge carriers in the ZnO, can be achieved by controlling the chemical synthesis parameters of the nanoparticles.