Diversity of electronic transitions and photoluminescence properties in nanocrystalline Mn/Fe-doped tin dioxide semiconductor films: An effect from oxygen pressure

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Transition metal (TM: Mn or Fe) doped tin dioxide (SnO2) films with the compositions of 5% (Sn0.95TM0.05O2) have been deposited on sapphire substrates by pulsed laser deposition under oxygen pressure (Po) varied from 10−4 to 1 Pa. The x-ray diffraction, scanning electron microscopy, and infrared spectra analysis show that different TM dopants can affect the variations of crystallization and lattice distortion. Moreover, x-ray photoelectron spectroscopies indicate that the effective Po during the growth does not change the valence state of Sn4+ in the Sn0.95TM0.05O2 films. The spectral behaviors of the films have been investigated in the photon energy range of 0.47-6.5 eV (2650-190 nm). From transmittance spectra, the shoulder structures become more prominent for the Sn0.95Fe0.05O2 film than those for the Sn0.95Mn0.05O2 film due to the Fe repelling effect of a stronger p-d hybridization. The refractive index values for the Sn0.95Mn0.05O2 film are found to be larger than those for the Sn0.95Fe0.05O2 film at the photon energy of 0.47 eV. The main peaks at about 1.9 and 2.2 eV in photoluminescence (PL) emission spectra for both Sn0.95Mn0.05O2 and Sn0.95Fe0.05O2 films can be observed, and it could be explained by the fact that the electrons in the conduction band of SnO2 relax to defect states and then radiatively recombine with the holes. From direct comparison of PL and transmittance results for the films, the electronic transition energies, the emission peaks’ intensities and positions are shown to present the Po dependent behavior. The distinct trends indicate that the incorporation of Mn and Fe elements can provide a significant difference in the crystalline and electronic band structure. It can be concluded that the oxygen pressure and dopant contributions are responsible for the adjustment of electronic band structures and result in different optical response behaviors for the Sn0.95TM0.05O2 films.

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