ORCID Profile
0000-0002-1098-9575
Current Organisation
Nanyang Technological University
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Publisher: Optica Publishing Group
Date: 10-09-2010
DOI: 10.1364/OE.18.020439
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2008
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2009
Publisher: American Scientific Publishers
Date: 07-2007
DOI: 10.1166/JNN.2007.434
Abstract: Energy shifts in the Si 2p levels of the five Si oxidation states Sin+ (n = 0, 1, 2, 3, 4) in the system of Si nanocrystals embedded in SiO2 matrix have been determined. The thermal annealing effect on the energy shifts has been studied. The result suggests that the Si nanocrystals and the SiO2 are thermally stable but the annealing can cause some structural deformations such as changes in the bond lengths and bond angles for the suboxides Si2O and SiO. The energy shifts generally show a linear dependence on the oxidation state n, suggesting that the energy shifts could be mainly determined by the nearest-neighbor oxygen atoms. It is shown that the chemical structures of the system are similar to those of the conventional SiO2/Si system in terms of the energy shifts.
Publisher: AIP Publishing
Date: 15-03-2011
DOI: 10.1063/1.3554833
Abstract: The bandgap and optical properties (dielectric functions and optical constants) of dome-shaped Ge nanocrystals (nc-Ge) with average sizes of ∼6 nm in height and ∼13 nm in diameter have been investigated using spectroscopic ellipsometry based on the Forouhi-Bloomer optical dispersion model. As compared to bulk crystalline Ge, the nc-Ge exhibited a bandgap expansion of ∼0.2 eV and a significant reduction in the dielectric function. The bandgap expansion and dielectric suppression are discussed in terms of the quantum confinement effect as well as the bond contraction model.
Publisher: Optica Publishing Group
Date: 08-07-2010
DOI: 10.1364/OE.18.015585
Publisher: American Chemical Society (ACS)
Date: 10-2004
DOI: 10.1021/JP0465276
Publisher: IOP Publishing
Date: 15-05-2002
DOI: 10.1143/JJAP.41.3047
Publisher: IOP Publishing
Date: 22-08-2002
Publisher: AIP Publishing
Date: 15-06-2009
DOI: 10.1063/1.3148248
Abstract: Influence of thermal annealing on electroluminescence (EL) from multiple-Si-implanted silicon nitride films has been investigated. A reduced injection current and an enhanced EL intensity have been obtained simultaneously by increasing the annealing temperature, which results in a higher EL quantum efficiency. In addition, four emission bands are identified, and their peak energies, intensities, and full widths at half maxima are found to change with annealing temperature. A model is proposed to illustrate the carrier transport, the mechanisms of the four emission bands, and the evolution of the EL bands with annealing as well. The two major bands and the minor ultraviolet band are explained in terms of the recombination of the injected electrons in either the silicon dangling-bond (≡Si0) states or the nitride conduction band with the injected holes in either the band tail states above the nitride valence band or the valence band itself, while the minor near infrared band is attributed to the Si nanocrystals formed in the thin film.
Publisher: American Chemical Society (ACS)
Date: 23-10-2002
DOI: 10.1021/JP0266805
Publisher: Elsevier BV
Date: 2006
Publisher: AIP Publishing
Date: 15-05-2007
DOI: 10.1063/1.2713946
Abstract: We report a study on the influence of charge trapping on electroluminescence (EL) from Si nanocrystal (nc-Si) distributed throughout a 30nm SiO2 thin film synthesized by Si+ implantation into an oxide film thermally grown on a p-type Si substrate. The electron and hole trapping in the nc-Si located near the indium tin oxide gate and the Si substrate, respectively, cause a reduction in the EL intensity. The reduced EL intensity can be recovered after the trapped charges are released. A partial recovery can be easily achieved by the application of a positive gate voltage or thermal annealing at hot temperatures (e.g., 120°C) for a short duration. The present study highlights the impact of charging in the nc-Si on the light emission efficiency and its stability of nc-Si light-emitting devices.
Publisher: AIP Publishing
Date: 26-01-2009
DOI: 10.1063/1.3068002
Abstract: Strong visible electroluminescence (EL) has been observed from a 30 nm silicon nitride thin film multiply implanted with Si ions and annealed at 1100 °C. The EL intensity shows a linear relationship with the current transport in the thin film at lower voltages, but a departure from the linear relationship with a quenching in the EL intensity is observed at higher voltages. The EL spectra show two primary EL bands including the predominant violet band at ∼3.0 eV (415 nm) and the strong green-yellow band at ∼2.2 eV (560 nm). Two weak bands including the ultraviolet band at ∼3.8 eV and the near infrared band at ∼1.45 eV emerge at high voltages. The evolution of each EL band with the voltage has been examined. The phenomena observed are explained, and the EL mechanisms are discussed.
Publisher: AIP Publishing
Date: 15-01-2010
DOI: 10.1063/1.3291103
Abstract: The band gap and optical properties (dielectric functions and optical constants) of Ge thin films with various thicknesses below 50 nm, which were synthesized with electron beam evaporation technique, have been determined using spectroscopic ellipsometry and UV-visible spectrophotometry. The optical properties are well described with the Forouhi–Bloomer model. Both the band gap and optical properties show a strong dependence on the film thickness. For film thickness smaller than ∼10 nm, a band gap expansion is observed as compared to bulk crystalline Ge, which is attributed to the one-dimensional quantum confinement effect. However, a band gap reduction was observed for thickness larger than ∼10 nm, which is explained in terms of the amorphous effect in the Ge layers.
Publisher: AIP Publishing
Date: 24-12-2012
DOI: 10.1063/1.4773367
Abstract: Effective control of room-temperature electroluminescence of n-ZnMgO -GaN light-emitting diodes (LEDs) over both emission intensity and wavelength is demonstrated. With varied Mg concentration, the intensity of LEDs in the near-ultraviolet region is increased due to the effective radiative recombination in the ZnMgO layer. Furthermore, the emission wavelength is shifted to the green/yellow spectral region by employing an indium-tin-oxide thin film as the dopant source, where thermally activated indium diffusion creates extra deep defect levels for carrier recombination. These results clearly demonstrate the effectiveness of controlled metal incorporation in achieving high energy efficiency and spectral tunability of the n-ZnMgO -GaN LED devices.
Publisher: AIP Publishing
Date: 15-05-2007
DOI: 10.1063/1.2730560
Abstract: Si nanocrystals (nc-Si) with different sizes embedded in SiO2 matrix have been synthesized with various recipes of Si ion implantation. The influence of nanocrystal size on optical properties, including dielectric functions and optical constants, of the nc-Si has been investigated with spectroscopic ellipsometry. The optical properties of the nc-Si are found to be well described by the four-term Forouhi-Bloomer model. A strong dependence of the dielectric functions and optical constants on the nc-Si size is observed. For the imaginary part of the dielectric functions, the magnitude of the main peaks at the transition energies E1 and E2 exhibits a large reduction and a significant redshift in E2 depending on the nc-Si size. A band gap expansion is observed when the nc-Si size is reduced. The band gap expansion with the reduction of nc-Si size is in good agreement with the prediction of first-principles calculations based on quantum confinement.
Publisher: Wiley
Date: 22-06-2007
Publisher: IOP Publishing
Date: 16-11-2004
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2009
Publisher: Elsevier BV
Date: 2004
Publisher: American Chemical Society (ACS)
Date: 18-12-2002
DOI: 10.1021/JP027027K
Publisher: IOP Publishing
Date: 05-06-2009
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2NR11154C
Abstract: Although the dielectric behavior of nanostructured semiconductors has been intensively investigated, the physics behind observations remains disputed with possible mechanisms such as quantum confinement and dangling bond polarization. Here we show that theoretical reproduction of the measured dielectric suppression of Ge nanocrystals asserts that the dielectric suppression originates from the shorter and stronger bonds at the skin-deep surface, the associated local densification and quantum entrapment of energy. Coordination-imperfection induced local quantum entrapment perturbs the Hamiltonian that determines the band gap and hence, the process of electron polarization consequently.
Publisher: American Scientific Publishers
Date: 07-2008
DOI: 10.1166/JNN.2008.128
Abstract: The information of band structure of silicon nanocrystal (nc-Si) embedded in SiO 2 thin films synthesized by Si ion implantation and subsequent thermal annealing at various temperatures has been obtained from spectroscopy ellipsometric (SE) analysis. The indirect band structure and the energy gap of the nc-Si are not affected by the annealing. In contrast, the photoluminescence (PL) spectra show a continuous evolution with the annealing. Six PL bands located at 415, 460, 520, 630, 760, and 845 nm, respectively, have been observed depending on the annealing temperature. The annealing at 1100 °C yields the strongest PL band at 760 nm (∼1.63 eV) with the intensity much higher than that of all the other PL bands. Based on the knowledge of the band structure, the 760 nm-PL band could be attributed to the indirect band-to-band transition of the nc-Si assisted by the Si—O vibration of the nc-Si/SiO 2 interface with the stretching frequency of ∼1083 cm −1 (& sim0.13 eV). On the other hand, the first four PL bands mentioned above could originate from different extended defects in the oxide matrix, while the 845-nm PL band could be related to the interface luminescent centers.
Publisher: AIP Publishing
Date: 31-08-2009
DOI: 10.1063/1.3224191
Abstract: A structure of indium tin oxide/SiO2 embedded with Ge nanocrystal (nc-Ge) -Si substrate was fabricated. The capacitance of the structure can be switched to a high-capacitance or low-capacitance state by an ultraviolet (UV) illumination. The increase (or decrease) in the capacitance is accompanied with the decrease (or increase) in the oxide resistance. The capacitance switching is explained in terms of the UV illumination-induced charging and discharging in the nc-Ge.
Publisher: The Electrochemical Society
Date: 2002
DOI: 10.1149/1.1505741
Publisher: AIP Publishing
Date: 05-11-2004
DOI: 10.1063/1.1805715
Abstract: We have determined both the effective masses and the barrier heights for electrons and holes in pure SiO2 and lightly nitrided oxides with various nitrogen concentrations up to 4.5 at %. In contrast to previous studies which were usually carried out by assuming a value for either the effective mass or the barrier height, this study does not make such an assumption. The approach is proven to be reliable by examining the result for the well-studied pure SiO2 thin films. It is observed that with the increase of the nitrogen concentration the effective masses increase while both the barrier heights and the energy gap decrease.
Publisher: Elsevier BV
Date: 07-2006
Publisher: Elsevier BV
Date: 04-2005
Publisher: IOP Publishing
Date: 05-12-2001
Publisher: AIP Publishing
Date: 05-03-2007
DOI: 10.1063/1.2711198
Abstract: The authors report the photon-induced conduction modulation in SiO2 thin films embedded with germanium nanocrystals (nc-Ge). The conduction of the oxide could be switched to a higher- or lower-conductance state by a ultraviolet (UV) illumination. The conduction modulation is caused by charging and discharging in the nc-Ge due to the UV illumination. If the charging process is dominant, the oxide conductance is reduced however, if the discharging process is dominant, the oxide conductance is increased. As the conduction can be modulated by UV illumination, it could have potential applications in silicon-based optical memory devices.
Publisher: Springer Science and Business Media LLC
Date: 13-11-2010
Publisher: IOP Publishing
Date: 10-10-2007
Publisher: IOP Publishing
Date: 21-08-2001
Publisher: AIP Publishing
Date: 28-09-2009
DOI: 10.1063/1.3240867
Abstract: The lasing characteristics of randomly assembled SnO2 nanowires, whose excitonic gain is attributed to the exciton states bounded to the surface defects, are studied from room temperature up to 500 K. It is found that the amount of excited carriers under the lasing conditions is well below the Mott density of SnO2 so that high pumping intensities have less influence on the radiative recombination mechanism and wavelength of the lasing peaks. Furthermore, the redshift of lasing peaks is mainly due to the reduction of bandgap energy of SnO2 with the increase of temperature.
Publisher: The Electrochemical Society
Date: 2009
DOI: 10.1149/1.3118524
No related grants have been discovered for Tupei Chen.