S. F. Yoon

Semiconducting boron carbonitride nanostructures: Nanotubes and nanofibers

Highly oriented boron carbonitride (BCN) nanostructures consisting of nanotubes and nanofibers have been synthesized by bias-assisted hot-filament chemical vapor deposition from the source gases of B2H6, CH4, N2, and H2. It is found that the B concentration of the BCN nanostructures increases with increasing B2H6 in the gas mixture, and the highest B concentration is 45 at. %. Photoluminescence spectrum shows that the BCN nanostructures, identified as B0.34C0.42N0.24, are semiconductors with a band gap energy of around 1.0 eV.

Time-resolved photoluminescence spectra of strong visible light-emitting SiC nanocrystalline films on Si deposited by electron-cyclotron-resonance chemical-vapor deposition

SiC nanocrystalline films on Si substrates deposited using advanced electron-cyclotron-resonance chemical-vapor deposition exhibit intense visible light emission at room temperature under laser excitation. Continuous-wave and time-resolved photoluminescence measurements for these SiC films were carried out at room temperature. The photon energy of the dominant emission peaks is higher than the band gap of cubic SiC. Room-temperature optical absorption measurements show a clear blueshift of the band gap of the samples with a decrease of the average size of the nanoclusters, indicating an expected quantum-confinement effect. However, the emission spectra are basically independent of the size. Temporal evolution of the dominant emissions exhibits double-exponential decay processes. Two distinct decay times of ∼200 ps and ∼1 ns were identified, which are at least two orders of magnitude faster than that of the bound-exciton transitions in bulk 3C–SiC at low temperature. Strong light emissions and short decay ...

Electron field emission enhancement effects of nano-diamond films

Abstract In this paper, electron field emission properties of nano-diamond films, which were prepared using either CH 4 /H 2 /N 2 or CH 4 /Ar microwave plasma enhanced chemical vapor deposition, were studied. X-ray photoelectron spectroscopy detection indicates that nitrogen was incorporated into the nano-diamond film grown in CH 4 /H 2 /N 2 mixture. This nano-diamond film shows a very low threshold electric field of 2.2 V/μm and a high emission current density of 720 μA/cm 2 at applied field of 6.4 V/μm. Nitrogen incorporation, high grain boundary density and sp 2 -bonded non-diamond components in the films are believed to be responsible for the electron emission enhancement.

Y-junction carbon nanotubes grown by in situ evaporated copper catalyst

Y-junction carbon nanotubes have been grown by hot-filament chemical vapor deposition for which a gas mixture of acetone and hydrogen was fed and in situ evaporated copper was supplied. Transmission electron microscopy images reveal that, two of three branching angles around the Y-junction are obtuse (>90°) while the other is sharp (<90°). The sharp branching angles ranging between 50° and 80° are nearly twice the bending angles of simple bend junctions. This indicates that the Y-junction can be presented in structure as a combination of two bend junctions. An atomic configuration involving six heptagons on the three saddle surfaces is proposed to understand the topological structure of the observed Y-junction carbon nanotubes.

Metamorphic InP/InGaAs double-heterojunction bipolar transistors on GaAs grown by molecular-beam epitaxy

InP/InGaAs double-heterojunction bipolar transistor (HBT) structures were grown metamorphically on GaAs substrates by solid-source molecular-beam epitaxy. A linearly graded InxGa1−xP (x varying from 0.48 to 1) buffer layer was used to accommodate the strain relaxation. The crystallinity of the buffer layer and the HBT structure was examined by x-ray diffractometry. Devices with 5×5 μm2 emitter area showed a typical peak current gain of 40, a common-emitter breakdown voltage (BVCEO) higher than 9 V, a current gain cut-off frequency (fT) of 46 GHz, and a maximum oscillation frequency (fmax) of 40 GHz.

Highly oriented rich boron B–C–N nanotubes by bias-assisted hot filament chemical vapor deposition

Abstract Highly oriented rich boron B–C–N nanotubes, prepared by bias-assisted hot filament chemical vapor deposition, have been examined by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The compositions of the nanotubes have been analyzed by Auger electron spectroscopy and electron energy loss spectroscopy. The results show that the compositions can be controlled by changing the B 2 H 6 concentration in the reactive gas mixture and the highest boron content of 45% at atomic percentage can be obtained for the B–C–N nanotubes. As a new kind of semiconducting material, the photoluminescence of the B–C–N nanotubes is also studied.

Growth of GaAs on vicinal Ge surface using low-temperature migration-enhanced epitaxy

In this article, we demonstrate the influence of substrate temperature during migration-enhanced epitaxy (MEE) process of GaAs epitaxy on a vicinal surface of Ge (100), 6° offcut towards the (111) plane. It was found that the offcut surface is not the sufficient condition for suppressing the formation of antiphase domains at the GaAs∕Ge interface. Rather, it has to be complemented by low substrate temperature during the MEE process. GaAs grown at 250°C, the lowest temperature among all the samples, exhibits the smoothest surface and best structural and optical qualities, as characterized by atomic force microscopy, cross-sectional transmission electron microscopy, and low-temperature photoluminescence, respectively. At this substrate temperature, As dimers are adsorbed onto the substrate surface more readily with negligible reevaporation, ensuring complete coverage on the Ge surface with double-atomic steps. Complete coverage by As proved to be crucial in preventing the occurrence of inversion boundaries,...

Rapid thermal annealing of GaNxAs1−x grown by radio-frequency plasma assisted molecular beam epitaxy and its effect on photoluminescence

The effect of rapid thermal annealing (RTA) on GaNAs films grown on GaAs (100) substrates by radio frequency plasma-assisted solid source molecular beam epitaxy was investigated by low-temperature photoluminescence (PL) and high-resolution x-ray diffraction (HR-XRD) measurements. GaNAs samples with N content of 1.3% and 2.2% determined by experimental curve fitting of x-ray rocking curve with the dynamical diffraction theory, exhibit an overall blueshift in energy of 67.7 meV and an intermediate redshift of 42.2 meV in the PL spectra when subjected to RTA at 525–850 °C for 10 min. The results suggest that the GaNAs layer may have undergone an intermediate substitutional–interstitial diffusion in addition to purely outdiffusion of nitrogen atoms. Samples annealed at 700–750 °C showed 1.7–2.1 times improvement in integrated PL intensity and 1.6–1.8 times reduction in PL full width half maximum as compared to the as-grown sample. The HR-XRD results show no significant changes in GaNAs lattice parameter betwe...

The effects of self-generated DC bias on the characteristics of diamond-like carbon films prepared using ECR-CVD

Abstract The deposition of diamond-like carbon (DLC) films from a mixture of hydrogen and methane using the electron resonance chemical vapour deposition (ECR-CVD) method with radio-frequency (RF) bias is reported. The structural characteristics of the DLC films were characterized using Raman spectroscopy. The effects of the self-generated DC bias resulting from the RF power on the optical gap, Raman spectra, infrared (IR) absorption and film hardness in depositions carried out at 7 and 15 mtorr process pressures were investigated. Under conditions of 100 W microwave power and for a DC bias variation ranging from −10 V to −200 V, there exists evidence from Raman scattering analysis to show an increase in the diamond-like characteristic in films deposited at low DC bias at both process pressures. The variation of the D and G line peak position and integrated intensity ratio ( I D I D ) in the Raman spectra correlates well with the film hardness profile. There does not seem to be a relationship between the variation of the CH absorption peak intensity in the IR spectra (bonded hydrogen content) and the optical gap, although films with the highest optical gap tend to show a relatively higher CH absorption peak intensity in the IR spectra. Films deposited at high DC bias showed a reduction in the CH infrared absorption, suggesting a reduction in the bonded hydrogen content.

Electronic band structures of GaInNAs/GaAs compressive strained quantum wells

The electronic structures of the Ga1−xInxNyAs1−y/GaAs compressive strained quantum wells are investigated using 6×6 k⋅p Hamiltonian including the heavy hole, light hole, and spin-orbit splitting band. By varying the well width and mole fraction of N in the well material, the effects of quantum confinement and compressive strain are examined. The curves of dependence of transition energy on well width and N mole fraction are obtained. The valence subband energy dispersion curves and TE and TM squared optical transition matrix elements of three possible quantum well structures for emitting 1.3 μm wavelength are given.