脈衝雷射蒸鍍法成長氧化釤鋅薄膜之結構、光學、磁性與電性研究

Abstract

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Samarium-doped zinc oxide (Sm:ZnO) thin films were grown by pulsed-laser deposition (PLD) on c-oriented sapphire substrates with Sm concentration ranging from 1 to 10 atomic percent (at.%). The oxygen partial pressure was 3×10^-1 mbar and the substrate temperature was 525°C during deposition. The structural, optical, electrical, and magnetic properties are reported.Composition of Sm:ZnO thin films were examined by x-ray photoelectron spectroscopy, and it shows the Sm concentration in the films slightly larger than the nominal concentration. X-ray diffraction patterns implies that Sm atoms are successfully incorporated into ZnO lattice. With increasing Sm content, the c-lattice constant decreases from 5.21 to 5.15 Å and the crystallite size decreases from 37.8 to 12.6 nm. Atomic force microscopy shows that all samples having circular shape grain surface, and the surface roughness is between 3.6 and 22.4 nm. The optical properties are investigated by photoluminescence, transmission spectroscopy, and ellipsometry. Photoluminescence results show that defects in Sm:ZnO thin films include zinc vacancy, zinc interstitials, oxygen vacancy, and oxygen interstitials. The defect density increases with increasing Sm content. Moreover, the transmittance spectra indicate the optical band gap increases from 3.30 to 3.41 eV and the exciton binding energy decreases from 70 to 30 meV.Resistivity of Sm:ZnO films is between 19.22 and 135.1 mΩ. Anomalous Hall effect was not observed, and all Sm:ZnO thin films are n-type. The carrier concentration and mobility are ranging from 2.7×〖10〗^18 to 21.9×〖10〗^18 cm-3 and 3.96 to 28.98 cm2/V·s, respectively. The resistances of all Sm:ZnO films decrease when irradiated with lasers of wavelengths of 450, 532, and 658 nm, and the normalized resistance response (NRR) is between 0.95‰ and 9.07‰. Bi-exponential function fitting of NRR shows two response time constant for both irradiated and unirradiated process. The shorter response time constant τ_1 is attributed to the electron-hole pair generation/recombination, with τ_(1,L)=1.2~18.6 s for the sample under irradiation and τ_(1,D)=2.5~73.2 s without irradiation. The longer response time τ_2 is attributed to the response of carriers trapped in deep level defects, with τ_(2,L)=69.5~910.0 s and τ_(2,D)=127.1~2729.2 s.Sm:ZnO thin films have potential at electronic and magnetic component, such as the photo detector, light-emitting applications, and Faraday rotator, due to high electron concentration, highest conductivity, short response time in photoconductivity, and high Verdet constant.