Laser-Induced Growth Device and Optical Properties of ZnO
Microcrystals
LIAO Yi-min1, YAN Yin-zhou1, WANG Qiang2*, YANG Li-xue3, PAN Yong-man1, XING Cheng1, JIANG Yi-jian1, 2
1. Faculty of Materials and Manufacturing, Institute of Laser Engineering, Beijing University of Technology, Beijing 100124, China
2. College of New Materials and Chemical Engineering, Beijing Institute of Petrochemical Technology, Beijing 102617, China
3. School of Printing and Packing Engineer, Beijing Institute of Graphic Communication, Beijing 102627, China
Abstract：ZnO is third-generation semiconductors which can be used as the carrier of ultraviolet photoluminescence and multi-resonance mode laser. In recent years, ZnO microcrystals prepared by optical vapor supersaturation precipitation (OVSP) have shown important advantages in photocatalysis, efficient multi-color light source and efficient electroluminescence. However, the high preparation cost and low production efficiency hinder the development of the large-scale device. In this work, we designed and built a set of growth devices with a working wavelength of 1 080 nm and a power of 18% (@2 500 W) laser heating. The height of the raw material rod was 6.5 mm, and the diameter was 8 mm. The results show that the morphology, structure, and luminescence properties of the products prepared by this device are very close to those prepared by the OVSP method, and the production efficiency is greatly improved (~500 %). The growth device successfully prepared acceptor-rich ZnO single crystal micro rods with complete hexagonal cross-section morphology. The diameter and length of ZnO micro rods are about 3.8 and 10~20 μm, respectively. Raman spectra show that the Raman peaks of ZnO micro rods are sharp, and the Raman mode at 437 cm-1 indicates that the ZnO micro rods are hexagonal wurtzite structures with good crystallinity. By analysing the PL spectra of ZnO micro rods, it was found that the ZnO microtubes prepared by the OVSP method had a similar ultraviolet bimodal structure, indicating that there exists an abundant zinc-vacancies acceptor. In the 80~280 K range, with the increase of temperature, the fluorescence intensity of ZnO microrods appears “thermal quenching-negative thermal quenching-thermal quenching” behavior. The negative thermal quenching behavior in the range of 166~200 K is related to the intermediate state energy level (trap center) at 477 meV below the conduction band bottom, and the thermal quenching phenomenon in the range of 200~280 K is related to the non-radiative recombination center at 600 meV below the conduction band bottom. The appearance of both is related to the prepared ZnO microrod oxygen vacancy (VO) defect. The laser growth device developed in this paper has high feasibility and practicability. This preparation method lays a technical foundation for the rapid batch growth of ZnO single crystal micro rods with rich acceptors and is also of great significance for its application in optoelectronic devices.
Key words：ZnO microcrystal; Laser material processing; Raman spectrum; PL spectrum
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