title: Realization of Cu-Doped p-Type ZnO Thin Films by Molecular Beam Epitaxy.
abstract: Cu-doped p-type ZnO films are grown on c-sapphire substrates by plasma-assisted molecular beam epitaxy. Photoluminescence (PL) experiments reveal a shallow acceptor state at 0.15 eV above the valence band edge. Hall effect results indicate that a growth condition window is found for the formation of p-type ZnO thin films, and the best conductivity is achieved with a high hole concentration of 1.54 × 10(18) cm(-3), a low resistivity of 0.6 Ω cm, and a moderate mobility of 6.65 cm(2) V(-1) s(-1) at room temperature. Metal oxide semiconductor capacitor devices have been fabricated on the Cu-doped ZnO films, and the characteristics of capacitance-voltage measurements demonstrate that the Cu-doped ZnO thin films under proper growth conditions are p-type. Seebeck measurements on these Cu-doped ZnO samples lead to positive Seebeck coefficients and further confirm the p-type conductivity. Other measurements such as X-ray diffraction, X-ray photoelectron, Raman, and absorption spectroscopies are also performed to elucidate the structural and optical characteristics of the Cu-doped p-type ZnO films. The p-type conductivity is explained to originate from Cu substitution of Zn with a valency of +1 state. However, all p-type samples are converted to n-type over time, which is mostly due to the carrier compensation from extrinsic defects of ZnO.
authors.affiliation: Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, United States.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Suja
authors.affiliation: Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, United States.
authors.forename: Sunayna B
authors.initials: SB
authors.lastname: Bashar
authors.affiliation: Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, United States.
authors.forename: Muhammad M
authors.initials: MM
authors.lastname: Morshed
authors.affiliation: Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, United States.
authors.forename: Jianlin
authors.initials: J
authors.lastname: Liu
keywords: Cu dopant; ZnO; molecular beam epitaxy (MBE); p-type; thin film