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Atomic layer deposition (ALD) of bismuth sulfide (Bi2S3) is demonstrated by the sequential exposure of bismuth­(III) bis­(2,2,6,6-tetramethylheptane-3,5-dionate) [Bi­(thd)3] and hydrogen sulfide (H2S) at 200 °C. A saturated growth rate of 0.34–0.37 Å/cycle was observed by in situ quartz crystal microbalance (QCM) and verified by ex situ X-ray reflectivity (XRR) measurements throughout the ALD temperature window. As-deposited Bi2S3 films were found to be polycrystalline in nature without any preferential orientation. In addition to the direct band gap at ca. 1.56 eV normally seen for Bi2S3, we also found evidence for an indirect band gap at ca. 1.03 eV. Ultraviolet photoelectron spectroscopy (UPS) and Seebeck measurements strongly support degenerate p-type conductivity of the as-grown thin films, in contrast to the n-type nature normally found in the literature. Temperature-dependent (70–300 K) electrical resistivity measurements showed that, in the temperature range of 70–100 K, variable-range hopping (VRH) is the dominant carrier-transport process whereas, above 100 K, clear deviations from the VRH transport equation were observed, implying a crossover from localized states to a band-like transport process.

Dopant-profile independent electron transport has been observed through a combined study of temperature dependent electrical resistivity and magnetoresistance measurements on a series of Ti incorporated ZnO thin films with varying degree of static-disorder. These films were grown by atomic layer deposition through in-situ vertical stacking of multiple sub-monolayers of TiOx in ZnO. Upon decreasing ZnO spacer layer thickness, electron transport smoothly evolved from a good metallic to an incipient non-metallic regime due to the intricate interplay of screening of spatial potential fluctuations and strength of static-disorder in the films. Temperature dependent phase-coherence length as extracted from the magnetotransport measurement revealed insignificant role of inter sub-monolayer scattering as an additional channel for electron dephasing, indicating that films were homogeneously disordered three-dimensional electronic systems irrespective of their dopant-profiles. Results of this study are worthy enough for both fundamental physics perspective and efficient applications of multi-stacked ZnO/TiOx structures in the emerging field of transparent oxide electronics.

We have grown $200 nm thick ZnO films on (0001) sapphire substrates using atomic layer deposition at different substrate temperatures ranging from $150 to 350 C. X-ray diffraction and photoluminescence spectra of these films showed that crystalline and compositional native defects were strongly dependent on the substrate temperature. Room temperature Hall measurement showed that all the films were degenerate with carrier concentration exceeding the Mott's critical density n c required for metallic conduction. The lowest value of room temperature resistivity $3.6 Â 10 À3 X cm was achieved for the film deposited at $200 C, which had an estimated carrier concentration $5.7 Â 10 19 cm À3 and mobility $30 cm 2 /V s. The films deposited both below and above $200 C showed increased resistivity and decreased mobility presumably due to the intensified defects and deteriorated crystalline quality of these films. To investigate the effect of disorder on the underlying charge transport mechanisms in these films, the electrical resistivity was measured in the temperature range of $4.2 to 300 K. The films grown at $150, 300, and 350 C were found to be semiconducting in the entire range of the measurement temperature due to the intensified disorder which impeded the metallic transport in these films. However, the films grown at $200 and 250 C showed a transition from metallic to semiconducting transport behaviour at lower temperatures due to the reduced defects and improved crystalline quality of these films. The observed semiconducting behaviour below the transition temperature for these films could be well explained by considering quantum corrections to the Boltzmann conductivity which includes the effect of disorder induced weak localization and coulomb electron-electron interactions. V C 2013 AIP Publishing LLC. [http://dx.

A clear signature of disorder induced quantum-interference phenomena leading to phase-coherent electron transport was observed in (Zn, Al)Ox thin films grown by atomic layer deposition. The degree of static-disorder was tuned by varying the Al concentration through periodic incorporation of Al2O3 sub-monolayer in ZnO. All the films showed small negative magnetoresistance due to magnetic field suppressed weak-localization effect. The temperature dependence of phase-coherence length (lφ∝T−3/4), as extracted from the magnetoresistance measurements, indicated electron-electron scattering as the dominant dephasing mechanism. The persistence of quantum-interference at relatively higher temperatures up to 200 K is promising for the realization of ZnO based phase-coherent electron transport devices.