John S. Bailey

Highly Transparent Conductive Electrode with Ultra-Low HAZE by Grain Boundary Modification of Aqueous Solution Fabricated Alumina-Doped Zinc Oxide Nanocrystals

Commercial production of transparent conducting oxide (TCO) polycrystalline films requires high electrical conductivity with minimal degradation in optical transparency. Aqueous solution deposited TCO films would reduce production costs of TCO films but suffer from low electrical mobility, which severely degrades both electrical conductivity and optical transparency in the visible spectrum. Here, we demonstrated that grain boundary modification by ultra-violet laser crystallization (UVLC) of solution deposited aluminium-doped zinc oxide (AZO) nanocrystals results in high Hall mobility, with a corresponding dramatic improvement in AZO electrical conductance. The AZO films after laser irradiation exhibit electrical mobility up to 18.1 cm2 V−1 s−1 with corresponding electrical resistivity and sheet resistances as low as 1 × 10−3 Ω cm and 75 Ω/sq, respectively. The high mobility also enabled a high transmittance (T) of 88%-96% at 550 nm for the UVLC films. In addition, HAZE measurement shows AZO film scatteri...

STRAIN SPLITTING OF THE GAMMA 5 AND GAMMA 6 FREE EXCITONS IN ZNO

High-quality ZnO crystals have been grown by vapor-phase techniques and by the hydrothermal method. Depending on the surface preparation technique, some hydrothermally grown crystals contain strain. These strains result in energy shifts of the free excitons as well as relaxation of the selection rules. The Γ6 unallowed exciton is observed in these samples without the application of a magnetic field. The Γ6 exciton is also observed to split in a strain field, consistent with the Γ9 symmetry for the top valence band in ZnO. The Γ5 and Γ6 excitons have been observed to split in the strain field. The splitting is believed due to combined strain and electron–hole spin exchange.

Large Scale Laser Crystallization of Solution-based Alumina-doped Zinc Oxide (AZO) Nanoinks for Highly Transparent Conductive Electrode.

A new method combining aqueous solution printing with UV Laser crystallization (UVLC) and post annealing is developed to deposit highly transparent and conductive Aluminum doped Zinc Oxide (AZO) films. This technique is able to rapidly produce large area AZO films with better structural and optoelectronic properties than most high vacuum deposition, suggesting a potential large-scale manufacturing technique. The optoelectronic performance improvement attributes to UVLC and forming gas annealing (FMG) induced grain boundary density decrease and electron traps passivation at grain boundaries. The physical model and computational simulation developed in this work could be applied to thermal treatment of many other metal oxide films.

Optical power limiting in ZnO crystals

We report optical power limiting in undoped single crystals of the wide band-gap semiconductor Zinc Oxide (ZnO). The ZnO crystals were grown at the Sensors Directorate of the Air Force Research laboratory using the hydrothermal method. The crystals are of high optical quality and are transparent in the visible part of the spectrum. The contributions of the real and imaginary parts of the third-order nonlinear optical susceptibility were studied using the Z-scan technique. The Z-scan experiments were carried out using picosecond pulses at 532 nm wavelength with the electric field polarization oriented orthogonal to the crystal c- axis. The nonlinear refractive index of the crystals is found to be negative. The ZnO samples exhibit two photon absorption and high damage thresholds. Our results indicate that the ZnO crystals may be good candidates for applications in optical power limiting and pulse stabilization.

High Quality Hydrothermal ZnO Crystals

Zinc Oxide crystals have historically been grown in hydrothermal autoclaves with a basic mineralizer; however, doubts have been raised about the quality of such crystals because they have often exhibited large x-ray rocking curve widths and low photoluminescence (PL) yield with large linewidths. Several ZnO crystals were grown hydrothermally and sliced parallel to the c-plane. This resulted in opposite surfaces (the C + and C - ) exhibiting pronounced chemical and mechanical differences. Different surface treatments were investigated and compared by PL both at room temperature and liquid helium temperatures, and by double axis X-ray rocking curve measurements. The high quality of hydrothermally-grown ZnO is substantiated by the narrow rocking curve widths and sharp PL peaks obtained. A critical factor in obtaining these results was found to be surface preparation.