Atmospheric and Aqueous Deposition of Polycrystalline Metal Oxides Using Mist-CVD for Highly Efficient Inverted Polymer Solar Cells.

Large scale, cost-effective processing of metal oxide thin films is critical for the fabrication of many novel thin film electronics. To date, however, most of the reported solution-based techniques require either extended thermal anneals or additional synthetic steps. Here we report mist chemical vapor deposition as a solution-based, readily scalable, and open-air method to produce high-quality polycrystalline metal oxide thin films. Continuous, smooth, and conformal deposition of metal oxide thin films is achieved by tuning the solvent chemistry of Leidenfrost droplets to promote finer control over the surface-local dissociation process of the atomized zinc-bearing precursors. We demonstrate the deposited ZnO as highly efficient electron transport layers for inverted polymer solar cells to show the power of the approach. A highest efficiency of 8.7% is achieved with a fill factor of 73%, comparable to that of conventional so-gel ZnO, which serves as an indication of the efficient vertical transport and electron collection achievable using this material.

Growth of α-Ga2O3 from Gallium Acetylacetonate under HCl Support by Mist Chemical Vapor Deposition.

α-Ga2O3 films were grown on a c-plane sapphire substrate by HCl-supported mist chemical vapor deposition with multiple solution chambers, and the effect of HCl support on α-Ga2O3 film quality was investigated. The growth rate monotonically increased with increasing Ga supply rate. However, as the Ga supply rate was higher than 0.1 mmol/min, the growth rate further increased with increasing HCl supply rate. The surface roughness was improved by HCl support when the Ga supply rate was smaller than 0.07 mmol/min. The crystallinity of the α-Ga2O3 films exhibited an improvement with an increase in the film thickness, regardless of the solution preparation conditions, Ga supply rate, and HCl supply rate. These results indicate that there is a low correlation between the improvement of surface roughness and crystallinity in the α-Ga2O3 films grown under the conditions described in this paper.

Analysis of dislocation defects in compositionally step-graded α-(Al x Ga1-x )2O3 layers.

The ultra-wide bandgap semiconductor α-Ga2O3 can be heteroepitaxially grown on a sapphire substrate. However, due to a lattice mismatch of about 4.6% with a sapphire substrate, many dislocation defects occur in α-Ga2O3 films. To reduce the dislocation density, compositionally step-graded α-(Al x Ga1-x )2O3 layers were fabricated on a c-plane sapphire substrate using mist CVD. TEM measurements revealed few dislocations in the initial layer of α-(Al0.96Ga0.04)2O3, but numerous dislocations were observed in the subsequent layer of α-(Al0.84Ga0.16)2O3. However, the step-graded α-(Al x Ga1-x )2O3 layers exhibited bending of the dislocations under both compressive and tensile strains due to compositional differences of α-(Al x Ga1-x )2O3, resulting in about 50% reduction of the dislocation density in the high-Ga-composition layer of α-(Al x Ga1-x )2O3. The introduction of multiple 50 nm α-Ga2O3 layers into the compositionally step-graded α-(Al x Ga1-x )2O3 layers resulted in a notable reduction in dislocation defects at the interface between the sandwiched α-Ga2O3 layers. It is assumed that the dislocations were bent by the strain caused by the composition change, resulting in a decrease in the number of dislocations. It is anticipated that further reduction of dislocation density will be achieved by optimizing the composition change and thicknesses of layers that provide effective strain for dislocation bending, and by stacking these layers.

The effects of oxygen flow ratio on the properties of Ag x O thin films grown by radio frequency magnetron sputtering.

The Ag x O thin film with various oxygen flow ratios (R[O2]%) deposited by radio frequency magnetron sputtering (RFM-SPT) has been studied. While adjusting R[O2]% from 0% to 30%, the Ag x O thin film transitioned from metal to semiconductor and/or insulator with different transparent appearances on the surface observed using X-ray diffraction (XRD) and transmittance measurement. At high oxygen flow ratios, the Ag x O film is multi-phased as a mixture of Ag(II)O and Ag2 (III)O3. In addition, the work function (ϕ) of those samples changes from 4.7 eV to 5.6 eV as measured by photoelectron yield spectroscopy (PYS). The compositional and chemical state changes that occur at the Ag x O surface during the increments of R[O2]% are evaluated by the relative peak intensities and binding energy shifts in X-ray photoelectron spectroscopy (XPS). With the incorporation of more electrons in chemical bonding, the oxygen-induced band forms. And combining all the results from transmittance (band gap confirmation), PYS (work function confirmation), and XPS (valence band position confirmation), the estimated band diagrams are given for the oxidation state of Ag x O with various oxygen flow ratios.

Characterization and study of high conductivity antimony-doped tin oxide thin films grown by mist chemical vapor deposition.

Antimony doped tin oxide thin films are grown at atmospheric pressure using a home-built mist chemical vapor deposition system, which is an environmental-friendly technique with low energy consumption. For obtaining high quality Sb:SnO x films, different solutions are used to support the film fabrication process. The role of each component in supporting solution is also preliminarily analyzed and studied. In this work, the growth rate, density, transmittance, hall effect, conductivity, surface morphology, crystallinity, component and chemical states of Sb:SnO x films are investigated. Sb:SnO x films prepared at 400 °C using a mixing solution of H2O, HNO3 and HCl show a low electrical resistivity of 6.58 × 10-4 Ω cm, high carrier concentration of 3.26 × 1021 cm-3, high transmittance of 90%, and wide optical band gas of 4.22 eV. X-ray photoelectron spectroscopy analyses disclose that the samples with good properties have high [Sn4+]/[Sn2+] and [O-Sn4+]/[O-Sn2+] ratios. Moreover, it is discovered that supporting solutions also affect the CBM-VBM level and Fermi level in the band diagram of thin films. These experimental results confirm that Sb:SnO x films grown using mist CVD are a mixture of SnO2 and SnO. The sufficient supply of oxygen from supporting solutions leads to the stronger combination of cations and oxygen, and the combination of cations and impurities disappear, which is one of the reasons for obtaining high conductivity Sb:SnO x films.

Control of swelling height of Si crystal by irradiating Ar beam.

It has been found that ion implantation can induce a swelling (step-height) phenomenon on crystal surface. In this paper, we studied about the control of swelling height of Si crystal by irradiating Ar beam under various parameters (fluence, charge and energy). These irradiation parameters were regulated by an irradiation facility that enables to achieve the multiple ionization. For both charges, the swelling height was studied with the various fluencies of two different charges Ar(1+) and Ar(4+). The swelling height increased with increasing the fluence. The swelling height was also studied by changing energy of Ar(4+) beam. The swelling height increased by increasing the energy. The obtained swelling heights are understood base on the contribution of ion-beam induced defect, which is evaluated by SRIM. By comparing with the previous results, it was found that the expansion phenomena also depend on irradiated ion. The swelling structures were found to be stable more than two months. The present results have shown that this method of producing swelling structure indicates the potential application to fabricate 3-D nanostructure.