Melissa A. Lane

Highly conductive epitaxial CdO thin films prepared by pulsed laser deposition

Epitaxial growth of both pure and doped CdO thin films has been achieved on MgO (111) substrates using pulsed laser deposition. A maximum conductivity of 42 000 S/cm with mobility of 609 cm2/V s is achieved when the CdO epitaxial film is doped with 2.5% Sn. The pure CdO epitaxial film has a band gap of 2.4 eV. The band gap increases with doping and reaches a maximum of 2.87 eV when the doping level is 6.2%. Both grain boundary scattering and ionized impurity scattering are found to contribute to the mobility of CdO films.

Indium-cadmium-oxide films having exceptional electrical conductivity and optical transparency: Clues for optimizing transparent conductors

Materials with high electrical conductivity and optical transparency are needed for future flat panel display, solar energy, and other opto-electronic technologies. InxCd1-xO films having a simple cubic microstructure have been grown on amorphous glass substrates by a straightforward chemical vapor deposition process. The x = 0.05 film conductivity of 17,000 S/cm, carrier mobility of 70 cm2/Vs, and visible region optical transparency window considerably exceed the corresponding parameters for commercial indium-tin oxide. Ab initio electronic structure calculations reveal small conduction electron effective masses, a dramatic shift of the CdO band gap with doping, and a conduction band hybridization gap caused by extensive Cd 5s + In 5s mixing.

First-principles calculations for understanding high conductivity and optical transparency in InxCd1−xO films

Abstract We investigate In x Cd 1− x O materials, where x =0.0, 0.031, 0.063 and 0.125, to understand their high electrical conductivity and optical transparency windows, using the full-potential linearized augmented plane wave (FLAPW) method. In addition, we employ the screened exchange LDA (sX-LDA) method to evaluate accurate band structures including band gap that is underestimated by the LDA calculations. The results show a dramatic Burstein–Moss shift of the absorption edge by the In doping, reflecting the small effective mass of the Cd 5s conduction band. The calculated direct band gaps, 2.36 eV for x =0.0 and 3.17 eV for x =0.063, show excellent agreement with experiment. The effective mass of the conduction band of CdO is calculated to be 0.24 m e (in the ▵ direction), in good agreement with an experimental value of 0.27m e , explaining its high electrical conductivity. The hybridization between the Cd 5s and the In 5s states yields complex many-body effects in the conduction bands: a hybridization gap in the conduction bands and a band-gap narrowing which cancels the further Burstein–Moss shift for higher In doping.

Growth, microstructure, charge transport, and transparency of random polycrystalline and heteroepitaxial metalorganic chemical vapor deposition-derived gallium-indium-oxide thin films

Gallium-indium-oxide films (Ga x In 2 - x O 3 ), where x = 0.0-1.1, were grown by low-pressure metalorganic chemical vapor deposition using the volatile metalorganic precursors In(dpm) 3 and Ga(dpm) 3 (dpm = 2,2,6,6-tetramethyl-3,5-heptanedionato). The films were smooth (root mean square roughness = 50-65 A) with a homogeneously Ga-substituted, cubic In 2 O 3 microstructure, randomly oriented on quartz or heteroepitaxial on (100) yttria-stabilized zirconia single-crystal substrates. The highest conductivity of the as-grown films was found at x = 0.12, with σ = 700 S/cm [n-type; carrier density = 8.1 × 10 1 9 cm - 3 ; mobility = 55.2 cm 2 /(V s); du/dT < 0]. The optical transmission window of such films is considerably broader than that of Sn-doped In 2 O 3 , and the absolute transparency rival or exceeds that of the most transparent conductive oxides known. Reductive annealing, carried out at 400-425 °C in a flowing gas mixture of H 2 (4%) and N 2 , resulted in increased conductivity (σ = 1400 S/cm; n-type), carrier density (1.4 x 10 2 0 cm - 3 ), and mobility as high as 64.6 cm 2 /(V s), with little loss in optical transparency. No significant difference in carrier mobility or conductivity is observed between randomly oriented and heteroepitaxial films, arguing in combination with other data that carrier scattering effects at high-angle grain/domain boundaries play a minor role in the conductivity mechanism.

Flux synthesis, structure and physical properties of new pseudo-binary REAl3−xGex compounds

Abstract New compounds in the system RE-Al-Ge (RE=Tb, Gd, Ho) were prepared in molten aluminum. Large, (up to 5 mm) single crystals of new pseudo-binary phases GdAl3−xGex, (x=0.1), TbAl3−xGex, (x=0.3), and HoAl3−xGex, (x=0.2) were recovered in high yield. The crystal structures were refined by single crystal X-ray diffraction techniques, and found to vary as a function of rare-earth element. Thus, GdAl3−xGex crystallizes in the Ni3Sn structure type (P63/mmc) of GdAl3. For the TbAl3−xGex the BaPb3 structure type (R-3m) is adopted, as it is for TbAl3. In the case of HoAl3−xGex, the structure type of HoAl3 is not stabilized, and the compound crystallizes in the BaPb3 structure (R-3m). Crystal data: GdAl3−xGex a=6.3115(4) A, c=4.6052(4) A, V=158.87(2) A3, P63/mmc (No. 194, Z=2); TbAl3−xGex a=6.1956(9) A, c=21.025(4) A, V=698.9(2) A3, R-3m (No. 166, Z=9); HoAl3−xGex a=6.1579(10) A, c=21.062(5) A, V=691.7(2) A3, R-3m (No. 166, Z=9). Charge transport properties indicate that these materials are good metallic conductors. At low temperatures they order antiferromagnetically, whereas above ∼50 K they are Curie–Weiss paramagnets. The temperature of maximum magnetic susceptibility (Tmax) is 5.93 K, 18.8 K, and 24.0 K for HoAl2.8Ge0.2, TbAl2.7Ge0.3, and GdAl2.9Ge0.1 respectively.