title: The thickness-dependent band gap and defect features of ultrathin ZrO2 films studied by spectroscopic ellipsometry.
abstract: The band gap and defect features of ultrathin ZrO2 films with varying thicknesses have been investigated by spectroscopic ellipsometry through the point-by-point data inversion method. The ε2-sprectra in the 3-6 eV range are extracted based on an optical model consisting of a Si substrate/effective ZrO2 film/air ambient structure where the effective ZrO2 film is a combination of interfacial layers and ZrO2. Evident widening of the band gap with a reducing size is observed when the effective ZrO2 films are below a critical thickness, somewhere between 8.80 nm and 17.13 nm. This is due to quantum-confinement and amorphous effects. Moreover, the sub-band-gap defects at interfacial layers and in bulk ZrO2 are identified and present strong thickness dependence as well. The interfacial defects at 3.26, 4.13, 4.43, and 4.77 eV mainly exist below the critical thickness and exhibit a significant suppression with increasing film thickness. The bulk defects at 4.15 eV and 4.46 eV dominate in ZrO2 films once they are over the critical thickness. The evolution of the band gap and defects is closely related to variance in the electronic structure of amorphous ZrO2. Our results may be helpful in understanding controversial problems concerning the size effect on ultrathin high-k oxide films and exploring the further miniaturization of electronic devices based on them.
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China. rjzhang@fudan.edu.cn.
authors.forename: Ji-Ping
authors.initials: JP
authors.lastname: Xu
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China. rjzhang@fudan.edu.cn.
authors.forename: Rong-Jun
authors.initials: RJ
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of ASIC and System, School of Microeletronics, Fudan University, Shanghai 200433, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China. rjzhang@fudan.edu.cn.
authors.forename: Zi-Yi
authors.initials: ZY
authors.lastname: Wang
authors.affiliation: Institute of Electronic Engineering, China Academy of Engineering Physics, Mianyang, Sichuan 621999, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Chen
authors.affiliation: Institute of Electronic Engineering, China Academy of Engineering Physics, Mianyang, Sichuan 621999, China.
authors.forename: Qing-Hua
authors.initials: QH
authors.lastname: Huang
authors.affiliation: State Key Laboratory of ASIC and System, School of Microeletronics, Fudan University, Shanghai 200433, China.
authors.forename: Hong-Liang
authors.initials: HL
authors.lastname: Lu
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China. rjzhang@fudan.edu.cn.
authors.forename: Song-You
authors.initials: SY
authors.lastname: Wang
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China. rjzhang@fudan.edu.cn.
authors.forename: Yu-Xiang
authors.initials: YX
authors.lastname: Zheng
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China. rjzhang@fudan.edu.cn.
authors.forename: Liang-Yao
authors.initials: LY
authors.lastname: Chen