Strong green emission in ZnO films after H2 surface treatment

• Main Authors: Li, T., Herng, T. S., Liang, H. K., Bao, N. N., Wong, J. I., Xue, J. M., Chen, Tupei, Ding, Jun
• Other Authors: School of Electrical and Electronic Engineering
• Format: Article
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/95985; http://hdl.handle.net/10220/11405
• Institution: Nanyang Technological University

Using a two-step fabrication technique (pulsed laser deposition (PLD) and H2 surface treatment), we fabricated ZnO thin films that could emit ultra-strong green emission with coexistence of random lasing phenomenon. After PLD deposition, the as-prepared undoped ZnO thin films (200–500 nm) were annealed in Ar 95%–H25% ambient at 500 °C. The H2 treatment led to the formation of a porous structure that creates substantial optical cavities (diameter ~1.3 µm). Surprisingly, these optical cavities tremendously amplified the green emission rather than ultraviolet (UV) emission. There was insignificant change in emission intensity after high-temperature annealing (700 °C) in O2 and acetone dipping, indicating the samples are thermally and chemically stable. The samples exhibited a high quantum yield of 32%. We studied the origin of this ultra-strong green emission using low-temperature photoluminescence, extensive structural study and cyclic annealing. The results suggested that neither hydrogen nor VO plays a role in green emission. The green emission was attributed mainly to the complex defects and the presence of structural defects in the porous structure. In addition, we demonstrated the feasibility of large-scale green emission ZnO fabrication via micro-size patterning, paving a way to practical optoelectronic applications.