• 대한기계학회논문집B
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• 제40권9호
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• pp.621-627
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• 2016

본 연구에서는 실험적 데이터를 근간으로 박막재료의 스펙트럼(spectrum) 분포 별 포논-표면 산란율을 직접 계산할 수 있는 모델을 제시했다. 실험 측정결과인 포논 평균자유행로(mean free path, MFP) 스펙트럼 분포 별 열전달 기여도로부터 스펙트럼 의존적 포논-표면 산란율을 직접 도출하는 모델을 개발했고, 이 모델을 아직 실험적 방법으로 포논-표면 산란율을 측정하지 못한 $Si_{0.9}-Ge_{0.1}$ 나노선(Nanowire, NW)에 적용하여, $Si_{0.9}-Ge_{0.1}$ NW 내 포논 MFP 스펙트럼 분포를 구하고, 주파수에 따른 포논 전달특성을 살폈다. 이를 바탕으로 $Si_{0.9}-Ge_{0.1}$ NW 단위길이당 포논-표면 산란율을 제시하여, 가로갈래 포논 주파수 의존성을 살폈다. 본 연구에서 제시한 모델은 향후 나노재료의 공학적 응용을 위한 나노구조물 열전달 해석모델 개발 및 나노재료 열전달 특성 조정(tailoring)을 위한 나노재료 최적설계에 활용될 수 있다.

• Bulletin of the Korean Chemical Society
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• 제12권4호
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• pp.387-392
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• 1991

We present a theoretical investigation of the inelastic atom-surface phonon scattering for a model He-Si(100) system by the classical trajectory-quantum forced oscillator(DECENT) method. Single and multi-phonon transition probabilities of normal modes are calculated for several initial beam orientations and several initial kinetic energies. In order to understand surface structure effects, the calculation has been done on both reconstructed and unreconstructed surfaces of the He/Si(100) system. The origin of mode specificity for energy transfer is discussed. The contribution of one, two, and multi-phonon events to the total energy transfer between 0 and 600 K is also given.

• E2M - 전기 전자와 첨단 소재
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• 제9권2호
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• pp.174-179
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• 1996

We present a new physically based analytical equation for electron effective mobility in MOS inversion layers. The new semi-empirical model is accounting expicitly for surface roughness scattering and screened Coulomb scattering in addition to phonon scattering. This model shows excellent agreement with experimentally measured effective mobility data from three different published sources for a wide range of effective transverse field, channel doping and temperature. By accounting for screened Coulomb scattering due to doping impurities in the channel, our model describes very well the roll-off of effective mobility in the low field (threshold) region for a wide range of channel doping level (Na=3.0*10$^{14}$ - 2.8*10$^{18}$ cm$^{-3}$ ).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.4-5
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• 2010

The surface phonon is defined as a coherent vibrational excitation of surface atoms propagating along the surface. It is characterized by a phonon dispersion curves, which were extensively studied in 1990's using helium atom scattering and high-resolution electron-energy-loss spectroscopy (HREELS)[1].The understanding is mainly based on the theoretical framework of a classical bond model or cluster calculations. The recent sample preparation and first principles calculations open the naval way to deep insight for surface phonon problems. The surface phonon dispersion on the hydrogen-terminated Si(111)-($1{\times}1$) surface [H:Si(111)] is the typical system and already reported experimentally [2] and theoretically [3], although the understandingis incomplete. The sample contaminated by the oxygen atoms on the surface and the calculations were also classical. In this study, firstly, we have prepared an ultra-clean H:Si(111) surface [4] and measured the surface phonon dispersion curvesusing HREELS. Secondly, we have performed first-principles density functional calculations with the projector augmented wave functionals, as implemented in VASP, using generalized gradient approximations. We used aslab of six silicon layers and both top and bottom surfaces were terminated with hydrogen atoms. Finally, we have compared with the surface phonon dispersion of deuterium-terminatedSi(111)-($1{\times}1$) surface[5] and led to our conclusions. The Si-H stretching and the bending modes are observed at 258.5 and 78.2 meV, respectively. These energies are the same as the previously reported values [2], but the energy-loss peaks at the lower energy regions are dramatically shifted. Through this combination study, we have formulated the procedure of preparing ultra-clean H:Si(111)/D:Si(111), which was confirmed by HREELS vibrational analysis. The Si surface will be utilized for further nano-physics research as well as for the materials for nano-fubrication.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.191.2-191.2
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• 2015

Details of carrier dynamics in self-assembled quantum dots (QDs) with a particular attention to nonradiative processes are not only interesting for fundamental physics, but it is also relevant to performance of optoelectronic devices and the exploitation of nanocrystals in practical applications. In general, the possible processes in such systems can be considered as radiative relaxation, carrier transfer between dots of different dimensions, Auger nonradiactive scattering, thermal escape from the dot, and trapping in surface and/or defects states. Authors of recent studies have proposed a mechanism for the carrier dynamics of time-resolved photoluminescence CdTe (a type II-VI QDs) systems. This mechanism involves the activation of phonons mediated by electron-phonon interactions. Confinement of both electrons and holes is strongly dependent on the thermal escape process, which can include multi-longitudinal optical phonon absorption resulting from carriers trapped in QD surface defects. Furthermore, the discrete quantized energies in the QD density of states (1S, 2S, 1P, etc.) arise mainly from ${\delta}$-functions in the QDs, which are related to different orbitals. Multiple discrete transitions between well separated energy states may play a critical role in carrier dynamics at low temperature when the thermal escape processes is not available. The decay time in QD structures slightly increases with temperature due to the redistribution of the QDs into discrete levels. Among II-VI QDs, wide-gap CdZnTe QD structures characterized by large excitonic binding energies are of great interest because of their potential use in optoelectronic devices that operate in the green spectral range. Furthermore, CdZnTe layers have emerged as excellent candidates for possible fabrication of ferroelectric non-volatile flash memory. In this study, we investigated the optical properties of CdZnTe/ZnTe QDs on Si substrate grown using molecular beam epitaxy. Time-resolved and temperature-dependent PL measurements were carried out in order to investigate the temperature-dependent carrier dynamics and the activation energy of CdZnTe/ZnTe QDs on Si substrate.

• 전자공학회논문지A
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• 제31A권8호
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• pp.34-45
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• 1994

We studied threshold voltages and I-V characteristics. considering short channel effect of the fully depleted thin film n-channel SOI MOSFET. We presented a charge sharing model when the back surface of short channel shows accumulation depletion and inversion state respectively. A degree of charge sharing can be compared according to each of back-surface conditions. Mobility is not assumed as constant and besides bulk mobility both the mobility defined by acoustic phonon scattering and the mobility by surface roughness scattering are taken into consideration. I-V characteristics is then implemented by the mobility including vertical and parallel electric field. kThe validity of the model is proved with the 2-dimensional device simulation (MEDICI) and experimental results. The threshold voltage and charge sharing region controlled by source or drain reduced with increasing back gate voltage. The mobility is dependent upon scattering effect and electric field. so it has a strong influence on I-V characteristics.

• JSTS:Journal of Semiconductor Technology and Science
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• 제14권5호
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• pp.518-524
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• 2014

The substrate doping concentration dependence of strain-enhanced electron mobility in (110)/<110> nMOSFETs is investigated by using a self-consistent Schr$\ddot{o}$dinger-Poisson solver. The electron mobility model includes Coulomb, phonon, and surface roughness scattering. The calculated results show that, in contrast to (100)/<110> case, the longitudinal tensile strain-induced electron mobility enhancement on the (110)/<110> can be increased at high substrate doping concentration.

• 전자공학회논문지D
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• 제35D권8호
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• pp.31-37
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• 1998

A new self-consistent hole mobility model that includes lattice and hole temeprature has been proposed. By including the lattice and hole temperatures as well as the effective transverse field and the interface fixed charge, the model predicted the saturation of hole drift velocity and showed the effects of coulomb scattering, surface phonon scattering, and surface roughness scattering. The calculated data by the model were compared with the reported experimental data and they were shown to agree quite well. The new model is expected to estimate the characteristics of very short channel devices in the in the hydrodynamic model simulation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1996년도 춘계학술대회 논문집
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• pp.51-54
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• 1996

This paper reports the studies of the inversion layer mobility in p-channel Si MOSFET's under hot-carrier degradated condition. The validity of relationship of hot carrier degradations between the surface effective mobility and field effect mobility and are examined. The effective mobility(${\mu}$$\_$eff/) is derived from the channel conductances, while the field-effect mobility(${\mu}$$\_$FE/) is obtained from the transconductance. The characteristics of mobility curves can be divided into the 3 parts of curves. It was reported that the mobility degradation is due to phonon scattering, coulombic scattering and surface roughness. We are measured the mobility slope in curves with DC-stress [V$\_$g/=-3.1v]. It was found that the mobility(${\mu}$$\_$eff/ and ${\mu}$$\_$FE/) of p-MOSFET's was increased by increasing stress time and decreasing channel length. Because of the increasing stress time and increasing V$\_$g/ is changed oxide reliability and increased vertical field.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 추계학술대회 논문집 학회본부
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• pp.131-135
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• 1989

Hot electron simulation of silicon using Monte Carlo method was carried out to investigate impact ionization characteristics near the drain of MOSFET's at 77 and 300K. We successfully characterized drift velocity and impact ionization at 77 and 300K employing a simplified energy band structure and phonon scattering mechanisms. Woods' soft energy threshold model was introduced to the Monte Carlo simulation of impact ionization, and good agreement with reported experimental results was resulted by employing threshold energy of 1.7 eV. It is suggested that the choice of the critical angle between specular reflection and diffusive scattering of surface roughness scattering may be important in determining the impact ionization charateristics of Monte Carlo simulation near the drain of MOSFET's.