Structural and Electrical Characterization of Pure and Al-Doped ZnO Nanorods.

Ivana Panžić,Vilko Mandić,Ivana Capan,Tomislav Brodar,Arijeta Bafti

doi:10.3390/ma14237454

Abstract

Pure and Al-doped (3 at.%) ZnO nanorods were prepared by two-step synthesis. In the first step, ZnO thin films were deposited on silicon wafers by spin coating; then, ZnO nanorods (NR) and Al-doped ZnO NR were grown using a chemical bath method. The structural properties of zincite nanorods were determined by X-ray diffraction (XRD) and corroborated well with the morphologic properties obtained by field-emission gun scanning electron microscopy (FEG SEM) with energy-dispersive X-ray spectroscopy (EDS). Morphology results revealed a minute change in the nanorod geometry upon doping, which was also visible by Kelvin probe force microscopy (KPFM). KPFM also showed preliminary electrical properties. Detailed electrical characterization of pure and Al-doped ZnO NR was conducted by temperature-dependent current–voltage (I–V) measurements on Au/(Al)ZnO NR/n-Si junctions. It was shown that Al doping increases the conductivity of ZnO NR by an order of magnitude. The I–V characteristics of pure and Al-doped ZnO NR followed the ohmic regime for lower voltages, whereas, for the higher voltages, significant changes in electric conduction mechanisms were detected and ascribed to Al-doping. In conclusion, for future applications, one should consider the possible influence of the geometry change of (Al)ZnO NRs on their overall electric transport properties.

Highlights

ZnO is a direct wide-bandgap (3.37 eV) semiconductor with a large exciton binding energy of 60 meV, high electron mobility, high breakdown electric field strength, high radiation tolerance, and high thermal conductivity [1,2], suitable for electronic, optoelectronic, and sensing applications
We investigated the most important electric properties of undoped and
The SEM micrographs confirmed that closely packed arrays of vertically aligned nanorods with approximately the same lengths were achieved for all synthesis conditions

Summary

Introduction

ZnO is a direct wide-bandgap (3.37 eV) semiconductor with a large exciton binding energy of 60 meV, high electron mobility, high breakdown electric field strength, high radiation tolerance, and high thermal conductivity [1,2], suitable for electronic, optoelectronic, and sensing applications. The tetrahedral coordination is typical for covalent bonding, but ZnO has a substantial ionic character. ZnO, where zinc atoms are present in excess in comparison to oxygen atoms, resides at the borderline between covalent and ionic semiconductors. It is a nonstoichiometric compound due to the excess of zinc atoms, and even undoped ZnO shows intrinsic n-type conductivity with high electron densities around 1021 cm−3. Zni , and the oxygen vacancies, V, are the dominant donors in undesired n-doped ZnO films. This remains controversial since impurities that are shallow donors, such as hydrogen [3], are unintentionally introduced and could cause the abovementioned behaviour

Methods

Results

Conclusion