| Transparent conducting oxides (TCOs), with high optical transparency in the visible region and low conductive resistivity, are widely utilized as optical window electrodes in photovoltaic devices, liquid crystal displays, and solar energy conversion devices. Among TCOs, ZnO, SnO2, and & In2O3 are the most commonly systems, which have been applied as passive transparent conductive windows in active semiconducting devices, such as pn junctions, field effect transistors, and ultraviolet lasers. However, these well-known material systems still have some limitations, such as instability of oxygen content, fatigue, and degradation. It is imperative to find alternative transparent materials, which can potentially exhibit better physical properties. Perovskite-structured oxide is an important class of materials due to the excellent physical properties, such as ferroelectricity, ferromagnetism, superconductivity, and piezoelectricity. With the aid of the ionic substitution process, TCOs with the perovskite structure have been recently explored, such as In, Sb, and La-doped SrTiO3, Nb-doped CaTiO3, and In-doped Cd3TeO6. Furthermore, the epitaxial all-perovskite multilayer heterostructures have attracted much attention due to the multiplicity for physical properties of perovskites and advantages in film growth. These all-perovskite multilayer heterostructures are promising candidates for innovative micro- and nanoelectronic devices. Therefore, it is crucial to fabricate high-quality perovskite films for the above-mentioned heterostructures and related applications.Alkaline earth stannates with the general formula ASnO3 (A= Ba, Sr, and Ca) is another perovskite system, which is frequently used in electronic industry owing to the interesting dielectric and gas-sensing properties. In particular, BaSnO3 (BSO) is an ideally cubic perovskite-type oxide, which behaves as a n-type semiconductor with a wide band gap and remains stable up to 1000℃. It has been used in thermally stable capacitors, humidity sensors, gas sensors, and has great potentials for epitaxial all-perovskite multilayer devices and future photovoltaic technology. Recently, a few studies have been made on the effects of acceptor and donor doping in BSO. Notably, La-doped BaSnO3 (BLSO) has drawn great attention due to its good performance. For example, Kim et al. reported single-crystal BLSO with a mobility of 320 cm2V-1s-1 for a carrier concentration of 8×1019 cm-3. It is the highest value reported for any TCOs, which can be applied in optoelectronic devices.Perovskite-structured Ba1-xLaxSnO3 (BLSO, x=0-0.10) films have been directly deposited on (0001) sapphire substrates by a sol-gel method. The effects of La substitution on the microstructure, morphology, and carrier density of the BLSO films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and Halleffect measurement. The main works are listed as following:(1) The effects of La substitution on the microstructure, morphology, and carrier density of the BLSO films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and Halleffect measurement. XRD analysis shows that all of the films are of a single perovskite phase and the calculated lattice constants agree well with the theoretical lattice parameters. The AFM and SEM pictures show that the BLSO films do not contain cracks with the root-meansquare surface roughness of 2 nm. Hall measurements show that the BLSO films have n-type conductivity.(2) The optical transmittance spectra of the BLSO (x=0-0.10) films were measured in the range of 2650-190 nm, as shown in Figure 5. All of the films exhibit a high transparency of more than 80% in the visible region, which is an important parameter for applications. In order to extract the dielectric functions and other physical parameters of the BLSO films, the transmittance spectra were analyzed by a multilayer model with the three-phase-layered structure (air/BLSO/substrate). It was found that there are two interband transitions (about 4 and 6 eV) and the peak energies increase linearly with increasing La concentration.(3) We report lattice vibration behaviors of transparent conducting Ba1-xLaxSnO3 films derived from far-infrared reflectance spectra at the temperature range of 105-300 K. Three main phonon modes can be observed at room temperature and the frequencies approximately decrease with increasing La concentration. A polar mode TO1 appears at about 137cm-1 and becomes unstable with decreasing the temperature. On cooling, the TO1 mode vanishes at 270,240,180 and 210 K for the films with x=0.00,0.02,0.04 and 0.06 and appears again with further decreasing the temperature for the La concentration of 0.00 and 0.02. |
PDF Full Text Request