Sang-Woo Kang

Low-temperature growth of layered molybdenum disulphide with controlled clusters

Layered molybdenum disulphide was grown at a low-temperature of 350u2009°C using chemical vapour deposition by elaborately controlling the cluster size. The molybdenum disulphide grown under various sulphur-reaction-gas to molybdenum-precursor partial-pressure ratios were examined. Using spectroscopy and microscopy, the effect of the cluster size on the layered growth was investigated in terms of the morphology, grain size, and impurity incorporation. Triangular single-crystal domains were grown at an optimized sulphur-reaction-gas to molybdenum-precursor partial-pressure ratio. Furthermore, it is proved that the nucleation sites on the silicon-dioxide substrate were related with the grain size. A polycrystalline monolayer with the 100-nm grain size was grown on a nucleation site confined substrate by high-vacuum annealing. In addition, a field-effect transistor was fabricated with a MoS2 monolayer and exhibited a mobility and on/off ratio of 0.15u2009cm2 V−1 s−1 and 105, respectively.

Wafer-scale production of highly uniform two-dimensional MoS2 by metal-organic chemical vapor deposition

Semiconducting two-dimensional (2D) materials, particularly extremely thin molybdenum disulfide (MoS2) films, are attracting considerable attention from academia and industry owing to their distinctive optical and electrical properties. Here, we present the direct growth of a MoS2 monolayer with unprecedented spatial and structural uniformity across an entire 8 inch SiO2/Si wafer. The influences of growth pressure, ambient gases (Ar, H2), and S/Mo molar flow ratio on the MoS2 layered growth were explored by considering the domain size, nucleation sites, morphology, and impurity incorporation. Monolayer MoS2-based field effect transistors achieve an electron mobility of 0.47 cm2 V-1 s-1 and on/off current ratio of 5.4xa0×xa0104. This work demonstrates the potential for reliable wafer-scale production of 2D MoS2 for practical applications in next-generation electronic and optical devices.

Nanoporous SiCOH/CxHy dual phase films with an ultralow dielectric constant and a high Young's modulus

We used plasma-enhanced chemical vapor deposition (PECVD) of allyltrimethylsilane (ATMS), consisting of an allyl group along with three methyl groups attached to silicon, to form a low dielectric constant (low-k) and high modulus SiCOH matrix. We found that the dielectric constant and mechanical properties of the low-k material are strongly affected by the selection of the precursor, processing conditions such as the deposition temperature and post-treatment, the introduction of a second labile phase, and the chemical structure and composition of the films. After porogen (pore generator) treatment with cyclohexene oxide (CHO), the resulting material exhibited a low dielectric constant with excellent mechanical and thermal properties, having k ∼ 2.4 and a Youngs modulus of 8.4 GPa. FT-IR and XPS results show that this is caused by the desorption of the labile phase (CxHy), the formation of Si–O cage-like structures, and changes in the chemical composition of films after thermal treatment. SiO2, SiO3, and SiO4 impart greater modulus and hardness to the films by increasing the stable component of Si–O in the SiCOH matrix.

Sensor based on chemical vapour deposition-grown molybdenum disulphide for gas sensing application

Over the past few decades, sensors based on field-effect transistors have drawn much attention. Initially three dimensional materials were used for sensing, which were later replaced by two dimensional materials because of their ease of manufacturing and large specific areas. Amongst the transition metal dichalcogenides, MoS2 has been widely used for the fabrication of sensors owing to its ability to differentiate between a charge donor and an acceptor analyte. In this work, we fabricated sensors using chemical vapour deposition grown-MoS2. MoS2 was grown on a p-Si/SiO2 substrate using Mo(CO)6 as a precursor, the growth was carried out by the sublimation of the precursor under a flow of high purity H2S at high temperature. The aim of this work is to achieve a level of sensitivity that would enable the detection of individual gas analytes upon adsorption to the MoS2 surface. To efficiently detect individual gas analytes upon adsorption to the surface, we used interdigitated electrodes in the device architecture to increase the area of the channels for analyte adsorption. We used CO2 and O2 gases, which acted as charge donors. A trilayer MoS2 film was examined, and the detection sensitivity for O2 was higher in comparison to CO2. The fabricated device showed significant sensitivity up to parts per million detection level.

Deposition of Copper Dots from Chemical Vapor Deposition with [ Cu ( I ) ( hfac ) ] 2 ( DVTMSO ) and [ Cu ( I ) ( hfac ) ] 2 ( HD )

Two copper(I) complexes with organic ligands, [Cu I (hfac)] 2 (DVTMSO) and [Cu I (hfac)] 2 (HD) (hfac=hexafluoroacetylacetonate, DVTMSO=1,2-divinyltetramethyl-disiloxane, HD=1,5-hexadiene), were synthesized and used for copper metallorganic chemical vapor deposition. In these compounds, two Cu(hfac) fragments are bonded by one neutral ligand forming unusual structure with respect to other Cu(I) complexes. The compounds exhibited relatively high volatility and stability when compared to other copper(I) precursors. By using the reported compounds as precursors, a continuous Cu layer was not formed but the Cu islands were only observed. Also, the shape and size of Cu islands are significantly changed as a function of the substrate temperature.

A study on the real-time decomposition monitoring of a metal organic precursor for metal organic chemical vapor deposition processes

This study proposes a method for monitoring the decomposition state of a metal organic precursor which is used for the metal organic chemical vapor deposition (MOCVD) system. As many kinds of precursors for MOCVD such as tetrakis(dimethylamido)titanium (TDMAT) are highly likely to decompose due to the instability of their chemical structure during processing, critical problems are generated for thin film formation and its yield in this case. Although real-time monitoring technology on the decomposition degree of these precursors is essential for metallization, metal gate or electrode processes for memory devices, both commercialized technology and fundamental research have scarcely been accomplished. Therefore, this study endeavors for acknowledgment by the semiconductor industry with a proposal for a real-time monitoring method on the decomposition degree of the precursor through an ultrasonic diagnosis method. However, it is difficult to perform a degradation mechanism analysis since measuring the viscosity and physical properties of TDMAT is complicated due to its sensitivity to air. Therefore, viscosity was measured using a Pd compound (tetrakis(triphenylphosphine)palladium(0), Pd(PPh3)4) which is stable in air and has a similar chemical structure to TDMAT.

Development of particle characteristics diagnosis system for nanoparticle analysis in vacuum

A particle characteristics diagnosis system (PCDS) was developed to measure nano-sized particle properties by a combination of particle beam mass spectrometry, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). It allows us to measure the size distributions of nano-sized particles in real time, and the shape and composition can be determined by in situ SEM imaging and EDS scanning. PCDS was calibrated by measuring the size-classified nano-sized NaCl particles generated using an aqueous solution of NaCl by an atomizer. After the calibration, the characteristics of nano-sized particles sampled from the exhaust line of the plasma-enhanced chemical vapor deposition process were determined using PCDS.

Real-Time Diagnosis of Nano-Sized Contaminant Particles Generated in TiN Metal Organic Chemical Vapor Deposition

We investigated characteristics of contaminant particles generated in titanium nitride (TiN) metal organic chemical vapor deposition (MOCVD) using tetrakis(dimethyl-amino-titanium) (TDMAT) as a precursor. Variation of the particle distribution generated before and after decomposition of TDMAT was estimated with the modified particle beam mass spectrometer (PBMS) in real-time. Particle size and concentration were sensitive to the change of the chemical status of TDMAT. When integrated absorbance of CH3 stretching features was increased, Particle size and concentration were bigger and higher, respectively. The degree of thermal decomposition of TMDAT was verified with in-situ Fourier transform infrared (FT-IR) spectroscopy and the morphology of films was measured by atomic force microscopy (AFM).

Observation of photoluminescence from large-scale layer-controlled 2D ß-Cu2S synthesized by the vapor-phase sulfurization of copper thin films

Two-dimensional (2D) copper chalcogenides (Cu2-x X where Xxa0=xa0S, Se, Te) have had much attention regarding various applications due to their remarkable optical and electrical properties, abundance, and environmentally friendly natures. This work indicates that highly uniform Cu2-x S (where 0xa0<xa0xxa0<xa01) nanosheets can be obtained by the two-step method of Cu deposition by sputtering with precisely controlled and extremely low growth rate followed by vapor-phase sulfurization. The phase transformations of thin Cu2-x S films upon the Cu seed layer thickness are investigated. A unique thickness-constrained synthesis process using vapor-phase sulfurization is employed here, which evolves from a vertical to lateral growth mechanism based on the optimization of the Cu seed layer thickness. Atomically thin 2D β-Cu2S film was successfully synthesized using the thinnest Cu seed film. We have systematically investigated the phase- and thickness-dependent optical properties of Cu2-x S films at room temperature. Micro-photoluminescence (PL) spectroscopy reveals that the 2D β-Cu2S film possesses a direct band gap with an energy of 1.1 eV while the PL intensities are greatly suppressed in the multilayer Cu2-x S (where 0xa0≤xa0xxa0<xa01).

Sulfurization-induced growth of single-crystalline high-mobility β-In2S3 films on InP

Metalorganic chemical vapor deposition was used to grow single-crystalline tetragonal β-In2S3 films on InP to afford covalently bonded In2S3/InP heterostructures, with the crystal structure of these films identified by high-resolution scanning transmission electron microscopy, X-ray diffraction, and Raman spectroscopy analyses, and the corresponding bandgap energies determined by photoluminescence measurements at room (300 K) and low temperatures (40 K). RT-PL measurements reveal the three peaks spectral emission at 464.3, 574.7, and 648.5 nm associated with luminescence from band-edge and two above conduction band-edge, respectively, although the LT-PL (40K) measurements of β-In2S3 film found two dominant peaks. Moreover, the above films exhibited n-type conductivity, with background electron concentration = 4.9 × 1015 cm–3, electron mobility = 1810.9 cm2 V–1 s–1, and resistivity = 0.704 Ω cm. Thus, single-crystalline β-In2S3 films deposited on InP are promising constituents of high-performance next-gene...