Well-width dependence of the emission linewidth in ZnO/MgZnO quantum wells
1 Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen, 361005, People's Republic of China
2 Department of Physics, Xiamen University, Xiamen, 361005, People's Republic of China
3 State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou, 510275, People's Republic of China
4 Department of Advanced Materials Science, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8561, Japan
5 Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing, 100083, People's Republic of China
Nanoscale Research Letters 2012, 7:605 doi:10.1186/1556-276X-7-605Published: 31 October 2012
Photoluminescence (PL) spectra were measured as a function of well width (LW) and temperature in ZnO/Mg0.1Zn0.9O single quantum wells (QWs) with graded thickness. The emission linewidth (full width at half maximum) was extracted from the emission spectra, and its variation as a function of LW was studied. The inhomogeneous linewidth obtained at 5 K was found to decrease with increasing LW from 1.8 to 3.3 nm due to the reduced potential variation caused by the LW fluctuation. Above 3.3 nm, however, the linewidth became larger with increasing LW, which was explained by the effect related with defect generation due to strain relaxation and exciton expansion in the QW. For the homogenous linewidth broadening, longitudinal optical (LO) phonon scattering and impurity scattering were taken into account. The LO phonon scattering coefficient ΓLO and impurity scattering coefficient Γimp were deduced from the temperature dependence of the linewidth of the PL spectra. Evident reduction of ΓLO with decreasing LW was observed, which was ascribed to the confinement-induced enhancement of the exciton binding energy. Different from ΓLO, a monotonic increase in Γimp was observed with decreasing LW, which was attributed to the enhanced penetration of the exciton wave function into the barrier layers.