Search

Molybdenum disulfide (MoS2), one of transition metal dichalcogenides, is a promising semiconductor material for electronic or optoelectronic devices due to its favorably electronic properties. However, in metal-oxide semiconductor field-effect transistor (MOSFET) structures using MoS2, electrical performances such as mobility and subthreshold swing are suppressed by the interface trap density between the channel and dielectric layers. Moreover, the electrical stability of such structures is compromised due to interface traps and that can be analyzed such as current hysteresis and transient characteristics. Here, we demonstrate MoS2 heterojunction field-effect transistors (HFET) by applying MoS2/p+-Si heterojunctions and achieve high performance characteristics, including a mobility of 636.19 cm2/(V·s), a subthreshold swing of 67.4 mV/dec, minimal hysteresis of 0.05 V, and minimized transient characteristics. However, the HFET devices with varying the channel length demonstrated degradation of electrical performance with increasing the overlap area of the channel and dielectric layers. These results regarding MoS2/p+-Si HFETs resulted in the structural optimization of high-performance electronic devices for practical applications. [ABSTRACT FROM AUTHOR]

InAs1−xSbx epilayer has nonlinearity bandgap energy between 180 and 350 meV according to the relative composition x of Sb at room temperature. For this reason, the wavelengths operating as a photodetector are in the mid-infrared (3–5 μm) and long-wavelength infrared range (8–12 μm). Photodetectors of these wavelengths can be used in the fields of pollutant detection, infrared thermal imaging, lidars, or optical countermeasures. Since the bandgap energy of InAs1−xSbx epilayer changes according to the relative composition of Sb, the measurement of InAs1−xSbx epilayer composition is crucial for predicting device characteristics. In this study, high-resolution X-ray diffraction was used to measure the mean composition of specimens without damaging the specimens of InAs1−xSbx epilayer. InAs1−xSbx thin films were grown epitaxially on the GaSb substrate having a similar lattice constant as the thin films by utilizing the molecular beam epitaxy method at various growth temperature conditions. Here, tilt of the growth direction in InAs1−xSbx thin films was observed despite having no off-cut angle of the GaSb substrate. Cases considering and not considering the tilt of the growth direction were analyzed to show a 3% difference in the relative composition of Sb in InAs1−xSbx thin films. Accordingly, this study revealed that the growth tilt of the epilayer must be taken into account when measuring the precise composition of InAs1−xSbx thin films grown on a GaSb substrate using high-resolution X-ray diffraction. [ABSTRACT FROM AUTHOR]

In most cases, despite the bandgap tuning flexibility of ternary semiconducting nanowires, phase mixing during nanowire growth is inevitable because of the surface energy competition between the bulk stable zinc blende (ZB) and the metastable wurtzite (WZ) phase. As the electronic structure of the grown nanowires depends on not only the composition but also the crystal structure of the nanowires, careful characterization of the phase mixing phenomena in the nanowires is significant. However, because most of the phase analysis of grown nanowires relies on transmission electron microscopy (TEM), the phase analysis should be local, requires destructive sample preparation, and has a high time cost. Here, we developed a modified reciprocal space mapping method exploiting laboratory-based high-resolution X-ray diffraction (HR-XRD) for phase analysis in a one-dimensionally grown nanowire array on a (111) Si substrate in one measurement sequence. The main difficulty of phase analysis in a nanowire array using HR-XRD is the overlap of the diffraction peaks resulting from the structural similarity between ZB and WZ. Using the proposed method, we could successfully separate the diffraction overlapping of the WZ and ZB phases and reveal the lattice constants, composition, and effect of the strain of an InAsxP1−x nanowire array corresponding to the growth conditions in one measurement sequence. We also found that the crystallinity of metastable WZ was considerably lower than that of the bulk stable ZB in InAsxP1−x and that a phase fraction of WZ and ZB in InAsxP1−x nanowire arrays could be tuned by adjusting their composition and diameter. [ABSTRACT FROM AUTHOR]

Research was conducted to examine the effects of atomic bond structure at the deposition surface on the crystallographic orientation dependence of carbon doping in gallium arsenide (GaAs). GaAs epilayers were prepared from semi-insulating GaAs substrates by atmospheric pressure in a vertical quartz reactor while epitaxial growths were carried out on different misoriented GaAs substrates. Results indicated CBr4 and CCl4 as excellent sources for the carbon doping of GaAs.