• Journal of the Korean Vacuum Society
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• v.15 no.2
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• pp.162-167
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• 2006

The symmetry of the conduction-band minimum of $GaAs_{1-x}N_{x}$ is probed by performing resonant Raman scattering (RRS) on thin layers of $GaAs_{1-x}N_{x}(x{\leq}0.7)$ epitaxially grown on Ge substrates. Strong resonance enhancement of the LO(longitudinal optical)-phonon Raman intensity is observed with excitation energies near the $E_0$ as well as $E_+$ transitions, However, in contrast to the distinct LO-phonon line-width resonance enhancement and activation of various X and L zone-boundary phonons brought about slightly below and near the $E_+$ transition, respectively, we have not observed any resonant LO-phonon line-width broadening or activation of sharp zone-boundary phonons near the $E_0$ transition. The observed RRS results reveal that the conduction-band minimum of GaAsN predominantly consists of the delocalized GaAs bulk-like states of ${\Gamma}$ symmetry.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.12
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• pp.1070-1078
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• 1998

A density of phonon is increased by application of electric field. At this time the phonon which has higher energy than around is called hot phonon is disappeared after 7 picosecond by scattering with electron and loss energy. Since the lifetime of phonon is very short, the effects of hot phonon can be neglected in the low speed semiconductor device, but it must be considered in high speed devices. DC and AC electric fields are applied to bulk GaAs, and the density of phonon is obtained and analyzed for its effects on electron velocity and electron distribution using Monte Carlo simulation method. Under high electric filed the density of hot phonon increased and energy of hot phonon is decreased by scattering with electron on the other hand the energy of electron is increased. Therefore electron move from central valley of conduntion band to satellite vallies and the valocity of electron decrease since the mass of electron in satellite vally is heavier than central vally. In millimeter wave frequencies, the effects of hot phonon increased at higher frequencies.

• Journal of Korean Vacuum Science & Technology
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• v.4 no.1
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• pp.27-32
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• 2000

We have studied the carrier relaxation of InAs/GaAs modulation-doped quantum dots depending on the excitation wavelength and modulation-doping concentration by using the time-ressolved spectroscopy. At the excitation below GaAs barrier band gap, the relaxation processes become very slow, implying to observe the phonon bottleneck effects. On the other hand, at the excitation far above GaAs band gap, phonon bottleneck effects are broken down due to Auger processes. Increasing modulation-doping concentration, the relaxation times, by virtue of Coulomb scattering between electrons in GaAs doped layer and carriers in InAs quantum dots, are observed to become fast.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.8
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• pp.611-617
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• 2001

The non-polar optical phonon scattering in the valence band depends on the masses, ratios, and types of mixtures of constituent atoms. Therefore, the random distribution of atoms in alloy semiconductors should be considered in the analysis of scattering mechanisms. For this purpose, the force equations of n atoms in a unit cell are expressed in a n x n matrix form to obtain the angular frequencies due to the acoustic and non-polar optical phonons. And, n is then assumed to be infinity. When this work is compared with other results published elsewhere, it is concluded that the independence of atomic displacement or amplitude of oscillation as ell as the infinite number of atoms in a unit cell must be taken into account for the random distribution of atoms in alloy semiconductors.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.552-554
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• 1999

Phonon scattering and impact ionization models have been presented to analyze hot carrier transport in high energy region, using full band model and Fermi's golden rule. We have investigated temperature dependent properties for impact ionization process of Si using realistic energy band structures at 77K and look. The realistic full band model, obtained from the empirical pseudopotential method with local from factors, is used to calculate scattering rate. The accurate calculation of impact ionization rate requires the use of a wavevector- and frequency-dependent dielectric function ξ ( q,$\omega$). The empirical phonon scattering rate P$\sub$ph/, is given by deriving from linear function for P$\sub$ph/ versus D(E) since the phonon scattering rate is linearly depended on density of states D(E). Impact ionization rate p,, is calculated from the first principle's theory. and fitted by modified Keldysh formula having power of above 2.

• Current Applied Physics
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• v.18 no.11
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• pp.1338-1344
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• 2018

Band parameters and superconductivity of yttrium hypocarbide ($Y_2C$) have been investigated. The computations are performed using first-principles pseudopotential method within a generalized gradient approximation. The equilibrium lattice parameters have been determined and compared with experiment. Moreover, the material of interest is found to be stiffer for strains along the a-axis than those along the c-axis. A band-structure analysis of $Y_2C$ implied that the latter has a metallic character. The examination of Eliashberg Spectral Function indicates that Y-related phonon modes as well as C-related phonon modes are considerably involved in the progress of scattering of electrons. By integrating this function, the value of the average electron-phonon coupling parameter (${\lambda}$) is found to be 0.362 suggesting thus that $Y_2C$ is a weak coupling Bardeen-Copper-Schrieffer superconductor. The use of a reasonable value for the effective Coulomb repulsion parameter (${\mu}^*=0.10$) yielded a superconducting critical temperature $T_c$ of 0.59 K which is comparable with a previous theoretical value of 0.33 K. Upon compression (at pressure of 10 GPa) ${\lambda}$ and $T_c$ are increased to be 0.366 and 0.89 K, respectively, showing thus the pressure effect on the superconductivity in $Y_2C$. The spin-polarization calculations showed that the difference in the total energy between the magnetic and non-magnetic $Y_2C$ is weak.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.9 s.339
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• pp.9-18
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• 2005

To make high-performance, low-power transistors beyond the technology node of 60 nm complementary metal-oxide-semiconductor field-effect transistors(C-MOSFETs) possible, the effect of electron mobility of the thickness of strained Si grown on a relaxed SiGe/SiO2/Si was investigated from the viewpoint of mobility enhancement via two approaches. First the parameters for the inter-valley phonon scattering model were optimized. Second, theoretical calculation of the electronic states of the two-fold and four-fold valleys in the strained Si inversion layer were performed, including such characteristics as the energy band diagrams, electron populations, electron concentrations, phonon scattering rate, and phonon-limited electron mobility. The electron mobility in an silicon germanium on insulator(SGOI) n-MOSFET was observed to be about 1.5 to 1.7 times higher than that of a conventional silicon on insulator(SOI) n-MOSFET over the whole range of Si thickness in the SOI structure. This trend was good consistent with our experimental results. In Particular, it was observed that when the strained Si thickness was decreased below 10 nm, the phonon-limited electron mobility in an SGOI n-MOSFT with a Si channel thickness of less than 6 nm differed significantly from that of the conventional SOI n-MOSFET. It can be attributed this difference that some electrons in the strained SGOI n-MOSFET inversion layer tunnelled into the SiGe layer, whereas carrier confinement occurred in the conventional SOI n-MOSFET. In addition, we confirmed that in the Si thickness range of from 10 nm to 3 nm the Phonon-limited electron mobility in an SGOI n-MOSFET was governed by the inter-valley Phonon scattering rate. This result indicates that a fully depleted C-MOSFET with a channel length of less than 15 m should be fabricated on an strained Si SGOI structure in order to obtain a higher drain current.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.278-281
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• 2011

The optical band gap energy for $SrTiO_3$ by reduction at high temperature was 3.15 eV. The reflectivity of reduced $SrTiO_3$ single crystals showed little variation, however, the reflectivity by the reduction condition had no effect. For the phonon mode at about 790 $cm^{-1}$, a blue-shift took place upon $N_2$ reduction and the decreased. However, a red-shift took place upon a $H_2-N_2$ reduction and the increased at the same phonon mode. With decreasing temperature the dielectric constant decreased rapidly. The thermal activation energies were 0.92-1.02 eV.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.512-513
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• 2018

Trap-assisted-tunneling (TAT) degrades subthreshold slope of real-world tunneling field-effect-transistors (TFET) and it should be considered in the simulation. However, its mechanism is not very well understood in line tunneling type L-shaped TFET (LTFET). This study investigates TAT mechanism in LTFETs using dynamic nonlcoal Schenk model. Both phonon assisted and direct band to trap tunneling events are considered in this study.

• Journal of the Korean Magnetic Resonance Society
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• v.27 no.4
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• pp.28-34
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• 2023

We study the linear-nonlinear quantum transport theory of Wannier-Landau transition system in the confinement of electrons by a square well confinement potential. We use the projected Liouville equation method with the ensemble density projection technique. We select the dynamic value under a linearly oscillatory external field. We derive the dynamic value formula and the memory factor functions in three electron phonon coupling systems and electron impurity coupling systems of two transition types, the intra-band transitions and inter-band transitions. We obtain results that can be applied directly to numerical analyses. For simple example of application, we analyze the absorption power and line-widths of ZnO, through the numerical calculation of the theoretical result in the Landau system.