Fabrication of high-quality ZnCdO epilayers and ZnO/ZnCdO heterojunction on sapphire substrates by pulsed laser deposition

摘要

ZnCdO is a promising partner of ZnO to form ZnO/ZnCdO heterojunction and quantum wells. High-quality Zn_(1-x)Cd_xO (0≤x≤9.60 at.%) films have been grown on c-plane sapphire substrates by pulsed laser deposition. XRD pattern confirmed all the ZnCdO films are of single hexagonal phase oriented along c-axis. A band gap of 2.949 eV at room temperature has been achieved. The relation between band gap of Zn_(1-x)Cd_xO system and Cd content x was expressed by E_g(x) = 1.023 × 10~(-4) x~2-0.034x+3.253 (0 at.%≤x≤ 100 at.%) according to the corrected first principles calculations. Furthermore, band offsets of ZnO/Zn_(1-x)Cd_xO (x = 9.60 at.%) heterojunction were characterized by X-ray photoelectron spectroscopy and valence-band offset of 0.203 eV was measured. A conduction-band offset of approximately 0.110 eV could be inferred from the measured valence-band offset. It is found that a type-Ⅰ alignment takes place at the interface. The accurate determination of the band alignment of ZnO/Zn_(1-x)Cd_xO heterojunction facilitates the design of optical and electronic devices based on ZnO/Zn_(1-x)Cd_xO.