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Atomically thin molybdenum disulfide (MoS2) is a two-dimensional semiconductor with versatile applications. The recent adoption of liquid molybdenum precursors in chemical vapor deposition has contributed significantly to the reproducible wafer-scale synthesis of MoS2 monolayer and few-layer films. In this work, we study the effects of the carrier gas flow rate on the properties of two-dimensional molybdenum disulfide grown by liquid-precursor-intermediate chemical vapor deposition on SiO2/Si substrates. We characterized the samples using Optical Microscopy, Scanning Electron Microscopy, Raman spectroscopy, and Photoluminescence spectroscopy. We analyzed samples grown with different nitrogen carrier flows, ranging from 150 to 300 sccm, and discussed the effect of carrier gas flows on their properties. We found a correlation between MoS2 flake lateral size, shape, and number of layers, and we present a qualitative growth model based on changes in sulfur provision caused by different carrier flows. We show how the use of liquid precursors can allow for the synthesis of homogeneous, single-layer flakes up to 100 µm in lateral size by optimizing the gas flow rate. These results are essential for gaining a deeper understanding of the growth process of MoS2. [ABSTRACT FROM AUTHOR]

Nanolayers of MoS2 can be grown to be used as active elements in nano-optoelectronic devices such as two-dimensional (2D) light emitters and optical detectors. The growth of 2D flakes might result in the formation of not only isolated triangles but also complex polycrystal flakes when different flakes interact during their in-plane expansion. In this paper, we investigate how monolayer MoS2 flakes of different shapes are affected by the biaxial strain resulting from the cooling process after chemical vapor deposition growth. The single- and polycrystal flakes are characterized at the nanoscale level by correlating morphological, electrical, and optical measurements and imaging. The main focus is given to the analysis of the exciton/trion photoluminescence (PL) components extracted from the spectra at different areas of the flake surface. According to the Raman imaging, the whole flake has built-in heterogeneous tensile strain, with the perimeter and the grain boundaries between the single-crystal parts of the poly flakes exhibiting a lower strain level (0.2–0.3%) and the central area being more strained (∼0.4%). At the perimeter and grain boundaries, the PL undergoes the strain-related blueshift accompanied by a weakening of the contribution of the long-wave trion to the spectrum and the trion binding energy. The trion formation is known to be proportional to a local electron concentration. The trion PL imaging compared to the surface potential mapping confirms a decrease in n-doping at the perimeter and grain boundaries, leading to the trion weakening. To confirm the results of electron drift to strained areas of the flake, creating the trion, the band bending at the tensile-strained flake has been theoretically calculated and modeled. The effect of edge defects at the perimeter and grain boundaries on the doping, which leads to the enhancement or inhibition of the trion formation depending on the edge and grain boundary interface type, is also discussed. [ABSTRACT FROM AUTHOR]

Orthorhombic κ-Ga2O3 thin films were grown for the first time on polycrystalline diamond free-standing substrates by metal-organic vapor phase epitaxy at a temperature of 650 °C. Structural, morphological, electrical, and photoelectronic properties of the obtained heterostructures were evaluated by optical microscopy, X-ray diffraction, current-voltage measurements, and spectral photoconductivity, respectively. Results show that a very slow cooling, performed at low pressure (100 mbar) under a controlled He flow soon after the growth process, is mandatory to improve the quality of the κ-Ga2O3 epitaxial thin film, ensuring a good adhesion to the diamond substrate, an optimal morphology, and a lower density of electrically active defects. This paves the way for the future development of novel hybrid architectures for UV and ionizing radiation detection, exploiting the unique features of gallium oxide and diamond as wide-bandgap semiconductors. [ABSTRACT FROM AUTHOR]

Photoelectronic properties of orthorhombic undoped κ-Ga2O3 epitaxial thin films, grown on sapphire substrates by metal–organic vapour phase epitaxy, were evaluated under X-ray irradiation (CuKα line, 8.05 keV) for the first time. Photoresponse linearity at low dose-rates (varying in the 10–200 μGy s−1 range), and excellent detection sensitivity (up to 342.3 μC Gy−1 cm−3), were demonstrated even at very low applied electric fields (down to 0.001 V μm−1). Photocurrent rise time was evaluated to be <0.5 s, and signal stability was assessed for exposure times up to 2 h, highlighting no degradation of the performance. These encouraging results, mostly due to the extremely low dark current measured (in the pA range), suggest that orthorhombic undoped κ-Ga2O3 is a promising material for the fabrication of sensitive and stable large-area X-ray detectors with minimum power consumption. [ABSTRACT FROM AUTHOR]

Unintentionally doped (001)‐oriented orthorhombic κ‐Ga2O3 epitaxial films on c‐plane sapphire substrates are characterized by the presence of ≈ 10 nm wide columnar rotational domains that can severely inhibit in‐plane electronic conduction. Comparing the in‐ and out‐of‐plane resistance on well‐defined sample geometries, it is experimentally proved that the in‐plane resistivity is at least ten times higher than the out‐of‐plane one. The introduction of silane during metal‐organic vapor phase epitaxial growth not only allows for n‐type Si extrinsic doping, but also results in the increase of more than one order of magnitude in the domain size (up to ≈ 300 nm) and mobility (highest µ ≈ 10 cm2V−1s−1, with corresponding lowest ρ ≈ 0.2 Ωcm). To qualitatively compare the mean domain dimension in κ‐Ga2O3 epitaxial films, non‐destructive experimental procedures are provided based on X‐ray diffraction and Raman spectroscopy. The results of this study pave the way to significantly improved in‐plane conduction in κ‐Ga2O3 and its possible breakthrough in new generation electronics. The set of cross‐linked experimental techniques and corresponding interpretation here proposed can apply to a wide range of material systems that suffer/benefit from domain‐related functional properties. [ABSTRACT FROM AUTHOR]