Highly resistive sputtered ZnO films implanted with copper

Abstract

Polycrystalline (0001)-oriented thin films of ZnO (thickness 120 nm) were deposited by rf magnetron sputtering and post-deposition annealed at 500 °C in oxygen (1 atm). The films were subsequently implanted with copper at doses over the range 1016 to 1017 ions/cm2. X-ray diffraction (XRD) indicates the compressive intrinsic film stress is largely relieved by the preimplantation anneal, and does not change when implanted or when further annealed after implantation, suggesting that the dominant cause of intrinsic stress is the atomic packing density rather than the crystallographic defect density. Resistivity measurements indicate that annealing of pure ZnO films causes the perpendicular resistivity to increase from 1.3 × 105 Ω · cm to 5 × 1010 Ω · cm. Copper implantation results in a lower resistivity of the order of 107 Ω · cm, but subsequent annealing actually increases resistivity beyond that of annealed nonimplanted ZnO to 3 × 1012 Ω · cm. It is proposed that copper increases the resistivity of those annealed films by trapping free electrons with the Cu 3d hole state occurring in CuO (formed predominantly during annealing). In order to check this, the oxidation state of the implanted copper was studied before and after annealing by x-ray photoelectron spectroscopy (XPS) and extended x-ray absorption fine structure (EXAFS). Three oxidation states of copper (Cu0, Cu1+, Cu2+) are detected in the implanted films, and postimplantation annealing results in oxidation of copper to the Cu2+ state, confirming that the presence of CuO in ZnO is associated with increased resistivity.

Properties of Cu-doped ZnO films by RF sputtering method: Thickness dependence

“…The appearance of a Cu 2p satellite implies that the Cu 2+ exists and the satellite intensity and position are also dependent on the atomic environment of the Cu 2+ . The Cu 2+ has a higher binding energy shoulder and weak satellite at approximately 943 eV [16]. Also, the Cu 3d orbital of Cu 1+ are filled as 3d 10 4s 0 (Cu)-2p 6 (O).…”

“…Also, the Cu 3d orbital of Cu 1+ are filled as 3d 10 4s 0 (Cu)-2p 6 (O). In contrast, the Cu 2+ has a 3d 9 4s 0 (Cu)-2p 6 (O) valence band configuration and may therefore trap electrons with the Cu 3d hole state [16]. Fig.…”

<title>Physiochemical characteristics of piezoelectric zinc oxide films grown by single-source chemical vapor deposition</title>

“…Measurements on sputtered zinc oxide thin films that have been annealed in oxygen (to remove oxygen vacancies) have been found to have an electrical resistivity of 5 x 10 10 Ω.cm 13 . In contrast, when the top electrode was sputtered onto the surface of the films for optical interferometric measurements, the electrical resistivity across the thickness of the film (from top electrode to bottom electrode) was very low (<5 x 10 4 Ω.cm).…”

Structural and optoelectronic properties of glucose capped Al and Cu doped ZnO nanostructures

“…The electron trap level of Cu doped ZnO was studied by Furukawa et al [11]. Also the other research groups found that the resistivity of the ZnO films increased with an increase in Cu concentration [9][10][11]. The current-voltage (I-V) characteristics of ZnO may be either linear or non-linear depending on the electrode-film contact as well as inherent defects controlled electron transport properties.…”