Aqueous lateral exitaxial overgrowth of ZnO layers on honeycomb patterned buffer layers through a Continuous Flow Reactor

• Main Authors: Shu-Han Yang, 楊舒涵
• Other Authors: Hou-Guang Chen
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/kx6rhd

碩士 === 義守大學 === 材料科學與工程學系 === 105 === In this study, the growth of high quality zinc oxide (ZnO) epitaxial layer is the major objective. To further reduce dislocation density, lateral epitaxial overgrowth (LEO) integrating with patterning processing had been proposed. In previous study, maskless LEO of ZnO on sapphire substrate in low temperature aqueous solution, through the assistance of line-patterned buffer layer, was reported. Although the dislocation density had been reduced, the effect of wing-tilt(a tilt angle of 0.1o) remained in the LEO ZnO layer. To suppress the wing-tilt effect, in our previous work, lateral epitaxial overgrowth of ZnO layer on hexagonal-patterned ZnAl2O4 buffer layers, with continuous flow reactors to conduct long duration epitaxial growth (>24h), can almost prevent the impact of wing-tilt effect. In this work, another pattern design with hexagonal symmetry, honeycomb pattern, was used to fabricated patterned ZnAl2O4 buffer layers on sapphire substrates. In this study, two different size of honeycomb patterned buffer layer was adopted to perform LEO. Aqueous lateral exitaxial overgrowth of ZnO layer was implemented on honeycomb patterned buffer layer through a conventional autoclave vessel or a continuous flow reactor, respectively. For conventional autoclave vessel, the crystal growth always needs to be interrupted to refresh the growth solution; meanwhile, the formation of the bubble on the center of honeycomb pattern obstruct the growth of ZnO in lateral directions; as a result, the fully coalesced ZnO layer cannot be achieved by the hydrothermal processing with conventional autoclave vessel. In contrast, for aqueous lateral exitaxial overgrowth of ZnO layer through the continuous flow reactor to implement long-duration hydrothermal growth, after LEO growth for 96h, the film was fully coalesced. It is evident that the LEO of ZnO through a continuous flow reactor can prevent the impact of gas bubbles. Based on X-ray diffraction rocking curve measurement, the wing-tilt was almost absent. The average dislocation density in the coalesced LEO layer was about 108 pitting/cm2. The microstructures and optical properties of coalesced ZnO film was implemented by transmission electron microscope and micro photoluminescence measurement.