Optical Properties Of Magnetic Doped Oxide Semiconductor Films

The transition metal doped wide band gap semiconductors with the dual characteristics of semiconductor materials and magnetic materials, and regulation of electronic and spin in the same kind of material can be achieved. Wide band gap diluted magnetic semiconductors (DMSs) combine their ferromagnetism with electrical conductivity and optical transparency, thereby opening up the possibility of other devices with unprecedented capabilities. Tin dioxide (SnO2) and titanium dioxide (TiO2) films have attracted considerable attention for its potential technological applications in the fields of spintronics, optoelectronics, and magnetoelectronics. Recently, kesterite compound Cu2ZnSnS4(CZTS) become research focus for its technological applications in photovoltaic devices. With the advantages of a near-optimal band gap (～1.5eV), high absorption coefficient (>104cm-1), earth-abundant elements, and low cost, CZTS has been considered as one of the most promising photovoltaic absorber materials. The absorber materials play an important role in determining the efficiency of photovoltaic devices. A detailed knowledge of the optical properties for semiconductor material is both of scientific interest and of important for devices applications. The electronic and optical properties of these semiconductor films have investigated. However, the optical properties of these semiconductor films are still limited and deficient. Especially, the temperature dependent optical properties of these materials have not been clarified. In this paper, the optical properties of Sn1-xMnxO2(SMO),Ti1-xFeO2and Cu2ZnSnS4(CZTS)semiconductor films have been investigated by transmittance spectra and photoluminescence spectra.(1) Optical properties of Sn1-xMnxO2films have been investigated; the effects of temperature and Mn composition on the optical band gap have been obtained. On the other hand, the relations between temperature and Urbach energy have been reported. The temperature dependence of electronic structures and optical constants in the SMO films have been investigated by transmittance spectra. Optical response functions have been extracted by fitting the transmittance spectra with the Adachi's model. It was found that the absorption edge presents a redshift trend with increasing Mn composition, and the optical band gap is varied between4.22and3.44eV. The band gap narrowing value [Eg(5.3K)-(300K)]has been reduced from98to3meV and linearly decreases with the Mn composition. Moreover, there are two temperature regimes for the Urbach energy, which could be explained by two empirical formulas in different temperature regimes.(2) Optical properties of Ti1-xFexO2films have been investigated; the UV-NIR dielectric functions have extracted by fitting the transmittance spectra; the effects of Fe composition on the photoluminescence have been obtained. The optical properties of Ti1-xFexO2films of have been studied by transmittance spectra and temperature dependent photoluminescence. The optical band gap is about3.60eV. Fe-doped samples exhibit a very weak luminescence due to the increase of oxygen vacancy concentration in TiO2. The PL spectra of undoped sample show the spectral lines at about1.78,1.94,2.13,2.25and2.37eV, which are attributed to oxygen vacancies, surface states and F+center.(3) The UV-NIR dielectric functions of CZTS films have determined by the temperature dependent transmittance spectra. The three higher-order interband electronic transitions can be observed and uniquely distinguished. The temperature dependence of phonon modes, dielectric functions, interband electronic transitions and absorption coefficient have been investigated. The A1phonon frequency of the kesterite CZTS film linearly decreases from about340to331cm-1with increasing the temperature from86to323K. The optical properties of CZTS films have been studied by temperature dependent transmittance spectra. Optical response functions have been extracted by fitting the transmittance spectra with the Tauc-Lorentz model. The fundamental band gap Eo, and higher energy critical points E1and E2are located at1.5,3.6, and4.2eV, respectively. Owing to the influences of electron-phonon interaction and the lattice expansion, the three interband transitions present a redshift trend with increasing the temperature.