Résumé
In theory, alloying ZnO with Cd it is possible to tune the bandgap from the visible to the UV spectral regions. The CdO Γ-Γ bandgap in the stable rock-salt phase is ~2.3 eV, but different calculations indicate that the bandgap is much lower in the wurtzite phase, 0.92-0.95 eV [1, 2]. The possibility tocontrol the bandgap also allows enhancing the carrier confinement through the development of heterostructures. Nevertheless, there are some problems related to the Cd solubility in the ZnO structure [3] and to the strong tendency of Cd to diffuse, which hinder the formation of high quality Zn1-xCdxO/ZnOheterostructures.In this work we present a detailed microstructure and optical analysis of high Cd content Zn1-xCdxO/ZnO multiple quantum well (MQW) nanowires grown by remote-plasma-enhanced metal-organic chemical vapor deposition. Six samples with ten Zn1-xCdxO/ZnO wells with widths from 0.7 to 10 nm are demonstrated, showing PL emissions ranging from 3.03 to 1.97 eV. The MQW nanowires with well thickness ≤ 2 nm show high radiative efficiencies compared with the thickest ones, consistent with the presence of quantum confinement. A single wurtzite phase and the MQW periodicity were confirmed by high resolution x-ray diffraction analysis. Finally, in order to quantify the Cd content and distribution along the structure, high resolution electron transmission microscopy and micro energy dispersive X-ray (micro-EDX) analysis were performed in single MQW-nanowires. A significant reduction of the Cd content is observed in the wells due to Cd interdiffusion to the barrier. Interdifussion effects modify the band strcuture and, consequently, the optical properties of the MQW heterostructure. These effects have to be considered in order to have a correct explanation of quantum confinement effects in Zn1-xCdxO/ZnO heterostructures.References[1] A. Schleife, C. Rödl , J. Furthmüller and F. Bechstedt, New J. Phys.,13, 085012 (2011).[2] A. Janotti, D. Segev and C. G. Van de Walle, Phys. Rev. B, 74, 045202 (2006).[3] K. Sakurai, T. Takagi, T. Kubo, D. Kajita, T. Tanabe, H. Takasu, Sz. Fujita and Sg. Fujita J. Cryst. Growth,514, 237 (2002).