The Study Of Properties In Noncompensated Fe-Sn Codoped In₂O₃ Films And Nanodot Arrays

Fe-doped In₂O₃ dilute magnetic semiconductor（DMS）have attracted considerable attention because of the high solubility of Fe ions into In₂O₃ lattice,which can effectively avoid the formation of secondary phases.The substitution of Fe dopant ions exhibit the mixed valences of Fe²⁺and Fe³⁺in the Fe doped In₂O₃,and it is wished that Fe²⁺is a kind of p-type dopant.The p-n pairs of Fe²⁺-Sn⁴⁺can be obtained by incorporation of Sn⁴⁺in Fe-doped In₂O₃DMS.Such codoping can be regarded as noncompensated p-n codoping,which can further enhance the solubility of dopant to achieve homogeneous DMS.Meanwhile,the magnetic and optical properties can be tuned by the concentration of p-n pairs.In this letter,the Fe-Sn codoped In₂O₃ films and nanodot arrays were prepared on Al₂O₃ substrates using the laser molecular beam epitaxy（LMBE）.The structure,valence,magnetic and optical properties of films and nanodot arrays were studied.The origin of room temperature ferromagnetism（RTFM）and the mechanism of localized surface plasmon resonance（LSPR）of the films and nanodot arrays were also discussed.The main results as follows:（1）(In_0.95-xSn_xFe_0.05)₂O₃（x=0.02,0.05,0.1,0.15,0.2）films were deposited on Al₂O₃substrates using the LMBE.The effect of Sn concentration and the thickness on the structure,valence,magnetic and optical properties of films have been investigated.The results of X-ray diffraction and X-ray photoelectric spectroscopy show that all the samples matches well with the single-phase cubic bixbyite of In₂O₃ structure.All the samples display obvious room temperature ferromagnetism.It is found that the Sn concentration has almost no effect on the saturation magnetic moment（M_s）of films.The M_s of films increases as the film thickness decreases.Optical measurements illustrate that the optical band gap shifts to higher energies as the Sn concentration increases.With further increase of Sn concentration to 20%,the shrinkage of optical band gap is observed due to the many-body interactions.As the film thickness decreases,the optical band gap of films decreases.（2）Fe-Sn codoped In₂O₃ nanodot arrays were deposited on Al₂O₃ substrates using the LMBE with the aid of AAO templates.The effect of Sn concentration and the size on the structure,valence,magnetic and optical properties of nanodot arrays have been investigated.The structural and compositional results reveal that the nanodot arrays show the single phase cubic In₂O₃ structure and Sn and Fe dopant ions substitute In³⁺sites of the In₂O₃ lattice with a tetravalence(Sn⁴⁺)and a mixed-valence(Fe²⁺/Fe³⁺),respectively.The nanodot arrays are uniform in size and well-ordered.All the samples display obvious room temperature ferromagnetism.It is found that the Sn concentration has almost no effect on the M_s of nanodot arrays,and the M_s of nanodot arrays increases as the nanodot size decreases.The free electrons mediate the long range ferromagnetic coupling between the BMPs is a possible mechanism in the nanodot arrays.The optical band gap shifts to higher energies as the Sn concentration increases.All the samples have the LSPR absorption peak in the near-infrared area,which can be tuned by the Sn concentration or sizes of nanodot arrays.