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

Abstract

ZnCdO is a promising partner of ZnO to form ZnO/ZnCdO heterojunction and quantum wells. High-quality Zn1−xCdxO (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 2.949eV at room temperature has been achieved. The relation between band gap of Zn1−xCdxO system and Cd content x was expressed by Eg(x)=1.023×10−4x2−0.034x+3.253 (0at.%≤x≤100at.%) according to the corrected first principles calculations. Furthermore, band offsets of ZnO/Zn1−xCdxO (x=9.60at.%) heterojunction were characterized by X-ray photoelectron spectroscopy and valence-band offset of 0.203eV was measured. A conduction-band offset of approximately 0.110eV 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/Zn1−xCdxO heterojunction facilitates the design of optical and electronic devices based on ZnO/Zn1−xCdxO.