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The low growth rate of mist chemical vapor deposition normally requires a long growth time to achieve coalescence in the epitaxial lateral overgrowth of α-Ga2O3 thin films on sapphire substrates. To address this issue, sub-μm features were patterned using laser interference lithography. Periodical stripes with a ∼590-nm pitch allowed the overgrowth of crack-free, void-free, and continuous thin films, while typical growth conditions using a low carrier gas flow rate and a low Ga precursor concentration were maintained. Coalescence was achieved even with a short growth time of <30 min and a low film thickness of <500 nm. Transmittance and x-ray diffraction spectra show that the film was predominantly in α-phase. Transmission electron microscopy (TEM) images reveal cup-top-like α-Ga2O3 regions of low dislocation density on the SiOx mask. Selected area electron diffraction and high-resolution TEM analyses confirm that an α-Ga2O3 layer was formed even on the top of the SiOx mask. Interestingly, the dislocations formed on the window areas did not bend toward the center of the masks; rather, a dislocation bending outward from the center was observed. This suggests the occurrence of early coalescence and/or atomic rearrangement. [ABSTRACT FROM AUTHOR]

Al-doped ZnO (AZO) thin films have been prepared by mist chemical vapor deposition and magnetron sputtering. The band gap shift as a function of carrier concentration in n-type zinc oxide (ZnO) was systematically studied considering the available theoretical models. The shift in energy gap, evaluated from optical absorption spectra, did not depend on sample preparations; it was mainly related to the carrier concentrations and so intrinsic to AZO. The optical gap increased with the electron concentration approximately as ne2/3 for ne≤4.2×1019 cm-3, which could be fully interpreted by a modified Burstein–Moss (BM) shift with the nonparabolicity of the conduction band. A sudden decrease in energy gap occurred at 5.4-8.4×1019 cm-3, consistent with the Mott criterion for a semiconductor-metal transition. Above the critical values, the band gap increased again at a different rate, which was presumably due to the competing BM band-filling and band gap renormalization effects, the former inducing a band gap widening and the latter an offsetting narrowing. The band gap narrowing (ΔEBGN) derived from the band gap renormalization effect did not show a good ne1/3 dependence predicated by a weakly interacting electron-gas model, but it was in excellent agreement with a perturbation theory considering different many-body effects. Based on this theory a simple expression, ΔEBGN=Ane1/3+Bne1/4+Cne1/2, was deduced for n-type ZnO, as well as p-type ZnO, with detailed values of A, B, and C coefficients. An empirical relation once proposed for heavily doped Si could also be used to describe well this gap narrowing in AZO. [ABSTRACT FROM AUTHOR]

The dependence of band gap shift on carrier concentration in n-type ZnO:Al is evaluated. The shift in energy gap is not dependable on sample preparations, but is related to the carrier concentrations and so intrinsic to Al-doped ZnO (AZO).

This work reports growth of α-(AlxGa1-x)2O3 single crystals with high incorporation of Al by a Mist Chemical Vapor Deposition two-chamber system, which was rationally designed to avoid side-reactions between different precursors during solution preparation for multi-component thin film growth. Multiple acceleration voltages were used in Energy Dispersive X-ray measurements to reliably obtain the Al composition x of the films. As a result, Vegard's law for lattice constants was verified and found to be valid in the α-(AlxGa1-x)2O3 system. However, Vegard's law for optical bandgaps, derived from different models, required an additional term to account for the bowing effect. At x = 0.71, the gaps were 7.74, 7.03, 7.26, and 7.34 eV as derived from the Tauc plots for the direct bandgap, indirect bandgap, Tauc-Lorentz model, and O'Leary-Johnson-Lim model, respectively. The two-chamber system provides reliable and effective control of the Al content in α-(AlxGa1-x)2O3 alloys and heterostructures. [ABSTRACT FROM AUTHOR]

We developed a thin-film transistor (TFT) with an amorphous-indium-gallium-zinc oxide (IGZO) channel and aluminium oxide (AlOx) gate dielectric stack that was formed using a solution-based atmospheric pressure chemical vapor deposition. A breakdown electric field of 5.9 MV/cm and a dielectric constant of 6.8 were achieved for the AlOx gate dielectric. The nonvacuum-processed IGZO TFT gave a field-effect mobility of 4.2 cm2 · V-1 · s-1 and an on/off current ratio of over 108. Moreover, the proposed deposition method is a powerful tool for material research to explore multicomponent oxide insulators and semiconductors. [ABSTRACT FROM PUBLISHER]

Transparent conducting Al-doped Zn1-xMgxO thin films were grown on glass substrates by chemical vapor deposition. The resistivity could be lowered to 10-3 Ω cm with optical transmittance above 85% in visible regions. The influence of carrier concentration on band-gap shift in Zn1-xMgxO alloys was systematically studied. The shift of energy gap could be fully explained by the Fermi-level band filling and band-gap renormalization effects. As the Mg content increased, the electron effective masses in Zn1-xMgxO (x=0–0.21) alloys increased from 0.30m0 to 0.49m0. The Al-doping efficiency was reduced with the increase in alloy composition. [ABSTRACT FROM AUTHOR]

The ultra-wide bandgap semiconductor α-Ga 2 O 3 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-Ga 2 O 3 films. To reduce the dislocation density, compositionally step-graded α-(Al x Ga 1- x ) 2 O 3 layers were fabricated on a c -plane sapphire substrate using mist CVD. TEM measurements revealed few dislocations in the initial layer of α-(Al 0.96 Ga 0.04 ) 2 O 3 , but numerous dislocations were observed in the subsequent layer of α-(Al 0.84 Ga 0.16 ) 2 O 3 . However, the step-graded α-(Al x Ga 1- x ) 2 O 3 layers exhibited bending of the dislocations under both compressive and tensile strains due to compositional differences of α-(Al x Ga 1- x ) 2 O 3 , resulting in about 50% reduction of the dislocation density in the high-Ga-composition layer of α-(Al x Ga 1- x ) 2 O 3 . The introduction of multiple 50 nm α-Ga 2 O 3 layers into the compositionally step-graded α-(Al x Ga 1- x ) 2 O 3 layers resulted in a notable reduction in dislocation defects at the interface between the sandwiched α-Ga 2 O 3 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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The Ag x O thin film with various oxygen flow ratios ( R [O 2 ]%) deposited by radio frequency magnetron sputtering (RFM-SPT) has been studied. While adjusting R [O 2 ]% 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 Ag 2 (III) O 3 . 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 [O 2 ]% 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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

α-Ga 2 O 3 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-Ga 2 O 3 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-Ga 2 O 3 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-Ga 2 O 3 films grown under the conditions described in this paper.

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 H 2 O, HNO 3 and HCl show a low electrical resistivity of 6.58 × 10 -4 Ω cm, high carrier concentration of 3.26 × 10 21 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 [Sn 4+ ]/[Sn 2+ ] and [O-Sn 4+ ]/[O-Sn 2+ ] 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 SnO 2 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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)