Group IV semiconductors, such as SiGe with a higher Ge fraction, are attracting attention as next-generation materials for high-mobility channel or thermal conductivity devices. Thus, we investigated the phonon dispersions of a Si 1-x Ge x (x = 0.72) alloy crystal by the inelastic X-ray scattering (IXS) method. In this method, measurement with an X-ray beam with a small spot size of 75 μm and resolution of millielectronvolts is possible due to the synchrotron technique. The longitudinal and transverse phonon spectra of optical and acoustic modes were measured from the Γ to the X point in the phonon energy band (0-70 meV) with millielectronvolt energy resolution. SiGe showed dispersion characteristics similar to those of Si and Ge crystals. It was confirmed that the IXS method is useful for obtaining properties of phonon dispersion.
ABSTRACTMoS2(1-x)Te2x, the alloy of MoS2 and MoTe2 was fabricated with just co-sputtering and the combination of co-sputtering with following thermal treatment in chalcogen ambient. Phase separation, where MoTe2 was segregated rather than S and Te being uniformly distributed, was observed for some samples. From the physical structure evaluation using XRD, it was shown that the samples that was sulfurized after unintentional oxidation during shelf time exhibited no phase separation. It was suggested that oxidation of Mo or amorphous nature of the film at the chalcogenization stage may prevent the phase separation. In addition, some samples were stored in desiccator for stability evaluation. It was revealed that the samples undergo oxidation to different extent depending on the carrier gas used in tellurization. Finally, the bandgap and band structure was evaluated for samples with different Te concentration. The bandgap showed bowing behavior for different Te concentration with the bowing parameter b = -1.21 eV. Combined with the bandgap evaluation, the valence analysis with XPS showed that the band structure shifted according to the Te concentration. The shift in bandgap allows flexible band alignment which is expected to expand the materials applicability.
In this study, sputtering deposition has been used to fabricate molybdenum disulfide (MoS2). The problem with sputtering deposition of MoS2 is desorption of S atoms from the film when the substrate is brought to high temperature in order to obtain high crystalline quality thin film. In this study, application of positive DC bias was employed to prevent S desorption even in high temperature process. It was revealed that when DC bias of +60 V is applied with respect to the substrate, with Argon partial pressure set to 0.09 Pa and RF power set to 225 W, films with S/Mo = 2.0 can be obtained even at the deposition temperature of 600°C. With S desorption suppressed by applying DC bias, sputtering deposition makes a favorable fabrication method for MoS2 and possibly other layered materials.
Raman spectroscopy was used to evaluate crystal quality of MoS2 films fabricated by RF magnetron sputtering with additional DC bias. Raman spectroscopy is a powerful tool to evaluate different physical properties of a film since phonons are sensitive to those properties. From the results of Raman spectroscopy measurements, improvement of crystal quality was shown corresponding to increase of the DC bias voltage, increase in the substrate temperature, and decrease of the deposition rate. Furthermore, the grain size was quantitatively evaluated by using the frequency deference between E12g and A1g Raman peaks. Through these evaluation it was revealed that the sputter parameter adjustment listed above (increase in DC bias voltage, etc.) increased grain size showing the film quality improvement quantitatively. Therefore, optimization of these sputtering parameters contributes to the fabrication of high quality MoS2 film at low-temperature.
ABSTRACTMolybdenum disulfide (MoS2) is expected to be applied for devices in various fields owing to its unique characteristics. Establishing a high-productivity manufacturing method which yields high quality films is an important and unresolved issue for the practical applications of MoS2. Among different techniques conducted by researchers all over the world, our approach is cold-wall metal-organic chemical vapor deposition, and we previously reported the deposition of MoS2 with i-Pr2DADMo(CO)3, a novel Mo precursor [S. Ishihara, et al., MRS Advances 3, 379-384 (2018).]. In this study, with the aim of further improving the quality of the MoS2 film using this new Mo precursor, various film formation conditions were controlled and the influence on the film quality was investigated. X-ray photoelectron spectroscopy, atomic force microscopy and Raman spectroscopy were used as evaluation techniques of the samples. As a result, mm-scale uniform film was formed with the deposition time less than 30 min. at temperature as low as 400 °C to 500 °C. It was revealed that maintaining low Mo/S supply ratio (SRMo/S) is crucial in fabricating high quality films.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.