Structural, Electrical, and Optical Effects of Metal Doping on ZnO Thin Films

Abstract

Doped ZnO thin films are prepared by reactive co‐sputtering of ZnO and a metal (Mn, Ti, W, and Zr). Structural and morphological analysis is done by means of SEM/EDX, XRD, and AFM. Electrical properties in terms of Volta potential are determined via Scanning Kelvin Probe (SKP), UV–VIS spectroscopy is employed to investigate optical properties. Band gaps Eg are obtained using Tauc plots. Doping of ZnO led to significant differences regarding structural, electrical, and optical properties. Morphology of doped ZnO tends to be smoother and more compact, as compared to the pristine ZnO. XRD measurements proved that W doped ZnO films exhibit an amorphous structure, whereas a secondary phase present in the Mn doped ZnO is strongly suggested. W and Mn as dopants lead also to special band gap positions in UV spectroscopy. W:ZnO exhibits a higher value for Eg whereas band gaps of Ti:ZnO and Zr:ZnO are similar to pristine ZnO. For Mn:ZnO two band gaps can be obtained. One is slightly higher and the other one is significantly lower than the one of pristine ZnO. Volta potential doubled when ZnO is doped with W, Zr, or Ti as compared to the pristine ZnO. Mn doped ZnO resulted in a lower Volta potential than pristine ZnO.

Strong Volta potential change in doped zinc oxide as a photoresponse to UV irradiation

“…As described in previous studies of doped ZnO deposited on glass substrates, W as a dopant severely disrupts the atomic structure of ZnO resulting in the formation of an amorphous layer. 11 The same effect is found in the current study for W : ZnO deposited on ITO. Al : ZnO has a very similar diffraction pattern to the pristine ZnO, whereas the (002) peaks of Ti, Mn and Zr doped ZnO (in ascending order) are shied towards lower diffraction angles.…”

“…All thin lms were prepared by reactive co-sputtering of ZnO and the individual dopant of interest (Al, Mn, Ti, W, or Zr). A schematic drawing of the experimental set-up for the preparation is given elsewhere, 11 and Fig. 1 depicts schematically the obtained layer structure.…”

“…In the case where foreign atoms are incorporated into interstitial sites and not as substitutional ions instead of Zn 2+ , a peak shi toward lower angles was reported. 11,27 Detailed studies performed on Aldoped ZnO demonstrated that Al is found in both substitutional and interstitial sites, 28,29 whereas Ti is found as interstitial. 27 The atomic radii of the dopants (206 pm for Zr, 193 pm for W, 176 pm for Ti and 161 pm for Mn) are all larger than that of Zn (135 pm), with the exception of Al (118 pm).…”

“…Theoretical calculations predict enhanced stability for doped amorphous ZnO. 8 As we have previously successfully fabricated amorphous W : ZnO on a glass substrate, 11 the aim here was to produce this amorphous layer on ITO-coated substrates and to evaluate the resulting optoelectronic and morphological properties. The chosen doping concentration of W is based on the ndings from DFT calculations in ref.…”

Enhanced photoreactivity of MOFs by intercalating interlayer bands via simultaneous NCO and SCu modification

“…When SCu was exchanged into the NIF crystals, the peaks in the XRD pattern of NIF‐SCu generally shifted toward larger angles, and the lattice parameters of the corresponding crystals decreased, but the diffraction peaks were all attributed to the ZIF‐8 structure. This result may be attributed to the smaller radius of the doped atom (Cu) compared with that of the main atom (Zn) and indicates that Cu was successfully incorporated into the NIF lattice 38,39 . The XRD pattern of NIF‐SCu shows rough peaks and impurity phases, which indicates that slight changes occurred in the surface structure of the crystal 40 .…”