Structure and Optical Properties of ZnO/MgxZn1-xO Multiple Quantum Wells Using a Y2O3 Buffer Layer on Si (111)
Wei-Lun Huang (黃偉綸)1*, Wei-Rein Liu (劉維仁)2, Liang-Hsun Lai (賴良訓)2, Chia-Hung Hsu (徐嘉鴻)2,3, Wen-Feng Hsieh (謝文峰)3, Mingh-Wei Hong (洪銘輝)4, Ray-Nine Kwo (郭瑞年)5
1Program for Science and Technology of Accelerator Light Source, National Chiao Tung University, Hsinchu, Taiwan
2National Synchrotron Radiation Research Center, Hsinchu, Taiwan
3Photonic, National Chiao Tung University, Hsinchu, Taiwan
4Physics, National Taiwan University, Taipei, Taiwan
5Physics, National Tsing Hua university, Hsinchu, Taiwan
* presenting author:Huang Wei-Lun,
A set of ten-period ZnO/MgxZn1-xO multiple quantum wells (MQWs) with well thickness varying from 1.6 to 4.8 nm have been grown by pulsed laser deposition on Si (111) substrates using a nm-thick Y2O3 buffer layer. Single phase MgxZn1-xO with Mg contents X = 0.33 ~ 0.36, as determined from lattice constant and optical absorption, was adopted as the barrier material. It was found that the quality of the MQWs was greatly improved by using the Y2O3 buffer layer on Si (111). The appearance of pronounced Pendellösung fringes in the X-ray crystal truncation rods is a clear evidence of the high crystalline quality of samples, because interface roughness and inhomogeneity in thickness and composition would decrease the phase coherence and suppress the fringes. High resolution cross-sectional transmission electron microscopy (TEM) images also confirmed the regularly arranged well and barrier layers. Low-temperature photoluminescence (PL) spectra showed localized exciton (LE) emissions at 3.53, 3.35 and 3.23 eV for the samples with well width of 1.6, 2.7 and 4.8 nm, respectively. For the MQWs with 2.7 and 4.8 nm thick wells, their exciton binding energy were less than the characteristic value of the bulk ZnO, 60 meV, indicating the presence of the quantum confined Stark effect. Furthermore, the observed phonon interaction decreased with decreasing well width. For the MQWs with 1.6 nm wells, its LE emission was blue-shifted with the exciton binding energy large than 60 meV, which are attributed to the dominant quantum confinement effect. Our results manifest both quantum confinement effect and quantum confined Stark effect induced by the built-in electric field play important roles in determining the physical properties of these high-quality MQWs.

Keywords: ZnO, MgxZn1-xO alloy, Multiple Quantum Wells, Superlattice, Photoluminescence