The Optical Properties of Zinc Oxide Grown by Atomic Layer Deposition

• Main Authors: Mong-Kai Wu, 吳孟楷
• Other Authors: 陳敏璋
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/65875863434501759648

碩士 === 臺灣大學 === 材料科學與工程學研究所 === 95 === Abstract This thesis studied the optical properties of the ZnO deposited by atomic layer deposition (ALD) on different substrates. It can be divided into three topics. The first topic is the epitaxial growth of ZnO on the SiC substrate. The columnar growth mode of ZnO on SiC was activated at high deposition temperatures. The photoluminescence measurements showed a high pumping threshold of stimulated emission, which was attributed to the lack of optical confinement due to the lower the refractive index of ZnO than that of SiC.. Two-step approach was used to grow ZnO with high crystalline quality at a low deposition temperature in the “ALD window”. By introducing a buffer layer deposited at high temperatures, highly orientated ZnO thin films could be grown on the buffer layer at a lower deposition temperature. The second topic is the stimulated emission in the polycrystalline ZnO thin films deposited on SiO2 The low-threshold stimulated emission in ZnO thin films was achieved. By controlling the film thickness and the annealing condition, the stimulated emission resulted from the electron-hole plasma (EHP) shifted toward larger photon energy and the lasing threshold increased. It could be attributed to the inter-diffusion between ZnO and SiO2, which reducds the many-body effects and modified the bandgap renormalization in ZnO. The third topic is the deposition of ZnO nanostructures by ALD. The initial island seeds as well as the selective growth of ZnO on homo- and hetero-interfaces were used to prepare the ZnO nanorods on the sapphire substrate. The ZnO island seeds were prepared by the initial ALD cycles followed with high-temperature post-annealing. Subsequent ALD growth proceeded preferentially on the ZnO island seeds over the sapphire substrate, leading to the formation of ZnO nanorods. Highly orientated ZnO nanorods with large-area uniformality and strong UV emission at room temperature were achieved. On the other hand, ZnO quantum dots were deposited into the voids between the SiO2 nanoparticles by using the excellent conformality of ALD. The ZnO dots were distributed uniformly in the SiO2 matrix. Because of the quantum confinement effects, significant blue-shift in the spontaneous emission spectrum was observed. We also presented the electroluminescence from the n-ZnO/SiO2/p-GaN heterojunction diode. The Mg deep-level emission in p-GaN appeared at low injection current density. With increasing the current density, the Mg deep-level emission from p-GaN saturated and electroluminescence from ZnO gradually dominated. Strong UV emission at reverse breakdown region was observed, which might be attributed to the impact ionization in GaN.