Effect of As incorporation on ZnO film structure and dielectric function


Effect of As incorporation on ZnO film structure and dielectric function

Vinnichenko, M.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.; Moeller, W.

Understanding the process of defect formation due to impurity incorporation is crucial for the control of electrical and optical properties of ZnO. The influence of As doping of ZnO on the film structure and properties is much less understood than the effect of N or Al incorporation. Therefore, this study is aimed at investigation of the ZnO film structure and dielectric function modification by doping with As. Two approaches to As incorporation have been used. In the first, the film has been deposited onto Al2O3 (0001) substrate by reactive pulsed magnetron sputtering of a Zn-As target at a temperature of 450 °C, thereby providing an As concentration of 2.0 at % in the layer. In the second approach, epitaxial films of ZnO deposited by the same method on Al2O3 (0001) substrate at 550 °C have been implanted with As+ ions (energy 300 keV) to provide the same As concentration. The film thickness has been adjusted to rule out any ion-beam intermixing effects at the ZnO/Al2O3 (0001) interface. The As concentration has been determined by particle induced X-ray emission, whereas film structure has been characterized by X-ray diffraction (XRD). Spectrscopic ellipsometry measurements have yielded the dielectric function of the films, as well as their thickness and roughness. The results have been compared with the structure and the optical properties of undoped ZnO.
Reactive pulsed magnetron sputtering of Zn target produces ZnO epitaxial layers with single-domain in-plane ordering and strong c-axis texture (rocking curve width of 0.37°). In contrast, ZnO:As layers are in nanostructured state as indicated by the broad peak at 34.2° on the XRD patterns. The doped layers also show much lower degree of in-plane ordering than the undoped films. XRD measurements suggest stronger ZnO structure modification due to the As+ ion implantation than to As incorporation during magnetron sputtering, although the impurity concentration is the same in both cases. The pole figure measurements show that the recrystallization of ZnO films heavily damaged by ion bombardment leads to a much more pronounced in-plane and off-plane textures of the samples annealed at 750-950 °C. The annealing also decreases film thickness which points to evaporation of the damaged layer [1]. The crystalline quality of the annealed ZnO is only slightly lower than that of the epitaxial undoped ZnO. Spectroscopic ellipsometry shows that the dielectric function in the spectral range around the band gap is sensitive to the crystalline quality of the films. The increased defect density in the doped layers broadens the oscillator used for the dielectric function parameterization. The band gap of the doped layers increases compared with that of the undoped ones.

[1] V.A. Coleman, H.H. Tan, C. Jagadish, S.O. Kucheyev, and J. Zou, Appl. Phys. Lett. 87, 231912 (2005).

Keywords: ZnO films; reactive magnetron sputtering; spectroscopic ellipsometry; x-ray diffraction

  • Poster
    13th International Conference on II-VI Compounds, 10.-14.09.2007, Jeju, Korea

Permalink: https://www.hzdr.de/publications/Publ-10489
Publ.-Id: 10489