Closed-Space Flux Sublimation Growth and Properties of (Cu-Mn)-Doped ZnO Films in Nanoneedle-Like Morphologies

Abstract

The Cu and Mn co-doped ZnO dilute magnetic semiconductor Zn1-x(Cu-Mn)xO films with unique nanoneedle like structure were deposited at ≤300°C by a two step closed space flux sublimation and periodic oxidation method. Morphology studies establish complex growth process involving a eutectic metal condensate on the substrate and spontaneous emergence of nanoneedle structure by oxidative process controlled by the vapor-liquid-solid mechanism. X-ray diffraction studies show that Zn1-x(Cu-Mn)xO films retain the typical wurtzite hcp structure of the un-doped ZnO. The absence of extraneous reflections indicates that neither the Mn and Cu dopant metal clusters nor their oxide phases are included in the nanostructure Zn1-x(Cu-Mn)xO films. The Raman peaks of Zn1-x(Cu-Mn)xO nanocrystalline films are consistent with the Raman active phonon modes for ZnO. The red shifted E2 (Low) and E2 (high) peaks confirm that Mn and Cu substitute at Zn site in the nanostructure Zn1-x(Cu-Mn)xO films. Optical transition at direct band gap energy occurs at 3.11 eV and an upward energy shift in the direct band to 3.58 eV is assigned to the quantum size effects of the nanoneedle structure of Zn1-x(Cu-Mn)xO films.