• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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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.

• 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.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.2
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• pp.189-194
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• 2018

Nowadays most integrated circuits are built using the bulk CMOS technology, but it has much difficulty in further reduction of the power consumption and die size. As a super low-power technology to solve such problems, the SOI technology attracts great attention recently. In this paper, the study results of the temperature dependency of the hot carrier effects in the n-channel MOSFETs fabricated on the thin SOI substrate were discussed. In spite that the devices employed the LDD structure, the hot carrier effects were more serious than expected due to the high series resistance between the channel region and the substrate contact to the ground, and were found to be less serious for the higher temperature with the more phonon scattering in the channel region, which resulted in reducing the hot electron generation.

• 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 Vacuum Society
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• v.12 no.S1
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• pp.36-39
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• 2003

Field-domain dynamics and current self-oscillations are theoretically studied in quantum-well (QW) negative-effective-mass (NEM) $p^{+}pp^{+}$ diodes when the electric field is applied along the direction of the well. The origin of current self-oscillations is the formation and traveling of electric-field domains in the p-base. We have accurately considered the scattering contributions from carrier-impurity, carrier-acoustic phonon, and carrier-optic phonon. It's indicated that, both the applied bias and the doping concentration largely influence the current patterns and self-oscillating frequencies, which lie in the THz range for the NEM $p^{+}pp^{+}$ diode with a submicrometer p-base. The complicated field-domain dynamics is presented with the applied bias as the controlling parameter.

• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.05a
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.304.2-304.2
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• 2014

Chalcogenides (Te,Se) and pnictogens(Bi,Sb) materials have been widely investigated as thermoelectric materials. Especially, Bi2Te3 (Bismuth telluride) compound thermoelectric materials in thin film and nanowires are known to have the highest thermoelectric figure of merit ZT at room temperature. Currently, the thermoelectric material research is mostly driven in two directions: (1) enhancing the Seebeck coefficient, electrical conductivity using quantum confinement effects and (2) decreasing thermal conductivity using phonon scattering effect. Herein we demonstrated influence of annealing temperature on structural and thermoelectrical properties of Bismuth-telluride-selenide ternary compound thin film. Te-rich Bismuth-telluride-selenide ternary compound thin film prepared co-deposited by thermal evaporation techniques. After annealing treatment, co-deposited thin film was transformed amorphous phase to Bi2Te3-Bi2Te2Se1 polycrystalline thin film. In the experiment, to investigate the structural and thermoelectric characteristics of Bi2Te3-i2Te2Se1 films, we measured Rutherford Backscattering spectrometry (RBS), X-ray diffraction (XRD), Raman spectroscopy, Scanning eletron microscopy (SEM), Transmission electron microscopy (TEM), Seebeck coefficient measurement and Hall measurement. After annealing treatment, electrical conductivity and Seebeck coefficient was increased by defect states dominated by selenium vacant sites. These charged selenium vacancies behave as electron donors, resulting in carrier concentration was increased. Moreover, Thermal conductivity was significantly decreased because phonon scattering was enhanced through the grain boundary in Bi2Te3-Bi2Te2Se1 polycrystalline compound. As a result, The enhancement of thermoelectric figure-of-merit could be obtained by optimal annealing treatment.

• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.560-565
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• 2003

M-doped (M=Al, Ni) ZnO thermoelectric materials were fully densified at low temperatures of 800∼1,000$^{\circ}C$ and their sintering characteristics and microstructural features were investigated. Electron microscopic analysis showed that the addition of NiO promoted tile formation of solid solution and caused actively grain growth. The addition of A1$_2$O$_3$ prevented the evaporation of pure ZnO at grain boundaries and suppressed the grain growth by the formation of secondary phase. In case of the addition of A1$_2$O$_3$ together with NiO, the specimen showed an excellent microstructure and also the SEM-EBSP (Electron Back-scattered Diffraction Pattern) analysis confirmed that it shows a superior grain boundary distribution to the others specimens. These microstructural characteristics induced by the addition of A1$_2$O$_3$ together with NiO may increase the electrical conductivity by the increase in carrier concentration and decrease the thermal conductivity by the phonon scattering effect and, consequently, improve the thermoelectric property.

• Journal of the Korean Institute of Telematics and Electronics
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• v.5 no.1
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• pp.1-5
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• 1968

GaAs single crystals were grown epitaxially from Ga solution with carrier concentrations in the range and electron mobilities between 7,500 and 9,300$\textrm{cm}^2$/v-sec. at 300$^{\circ}$K, and 50,000 and 95,000 $\textrm{cm}^2$/V-sec. at 77$^{\circ}$K. A comparison of the theoretical and experimental curves for the mobility vs. temperature indicates that the significant scattering mechanisms are ionized impurities and phonons in the temperature range of 77$^{\circ}$K to 439$^{\circ}$K. This indicates that the epitaxial layers do not contain other mobility limiting imperfections to a significant degree. Photoluminescence spectra of the. epitaxial layers did not show any emission due to deep lying imperfection leve1s.