Synthesis and Optical Properties of Undoped and Aluminum Doped ZnO Nanowires for Optoelectronic Nanodevice Applications

Abstract

Zinc oxide (ZnO) is a major wide band gap semiconductor material for optoelectronic and photonic devices because of its exceptional optical properties, arising from the combination of a wide band gap (~3.37 eV) and a large exciton binding energy (~60 meV). In this paper, the effects of Al doping on the optical properties of the ZnO nanowires are studied. In this paper, the doping effects of Al on the ZnO nanowires are studied. Results show the Al enhanced the UV photoluminescence emission in ZnO. With increasing optical excitation, a clear difference in the NBE photoluminescence peak characteristics of ZnO nanowires is observed when Al is introduced. Undoped nanowires exhibit a clear redshift of this emission peak above a certain threshold corresponding to the onset of bandgap renormalization effect . Furthermore, the measured integrated intensity of the near-band edge (NBE) emission changes from a free-excitonic behavior at lower excitation powers into a bimolecular radiative recombination at higher excitation powers beyond that same threshold level. By contrast, in Al-doped nanowires, there is no such peak shift in the same range of excitation power and only excitonic recombination process is observed, which is attributed to the incorporation of Al donors and the higher exciton binding energy in Al-doped ZnO. This makes Al-doped ZnO a promising platform for room-temperature polariton `lasers' because excitons could be preserved at high pump intensities.