Browsing by Author "Hsieh, MT"

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Effect of nitrogen incorporation into InAs layer in InAs/InGaAs self-assembled quantum dots
(2005-09-01)
Chen, JF
;
Hsiao, RS
;
Chen, YC
;
Chen, YP
;
Hsieh, MT
We present the results of nitrogen. incorporation into the InAs layer in InAs/InGaAs quantum dots (QDs). We show that this incorporation causes an asymmetric photoluminescence (PL) line shape and abnormally, large redshift of the PL peak from the quantum dots as temperature increases. In addition, this incorporation causes a large series resistance and a rapid increase in reverse current at a bias corresponding to the QD region. This effect is due to the formation of a deep trap at 0.34-0.41 eV, which depletes the carriers in the QD region. This depletion gives rise to a geometric resistance-capacitance time-constant effect for the ac conductivity of the free electrons in the top GaAs layer. This trap markedly alters the emission properties of the QD structure. The ac conductivity of the QD structure is governed by the thermal activation of trapped electrons rather than the electron emission from the QD confined states. This incorporation significantly increases the electron emission time from the QD region and, thus, can be used intentionally to modify the emission properties of the QD structure.
Properties of covalently bonded layered-silicate/polystyrene nanocomposites synthesized via atom transfer radical polymerization
(2005-02-01)
Li, CP
;
Huang, CM
;
Hsieh, MT
;
Wei, KH
;
材料科學與工程學系
Covalently bonded layered silicated/polystyrene nanocomposites were synthesized via atom transfer radical polymerization in the presence of initiator-modified layered silicate. The resulting nanocomposites had an intercalated and partially exfoliated structure, as confirmed by X-ray diffraction and transmission electron microscopy. The thermal properties of the nanocomposites improved substantially over those of neat polystyrene. In particular, a maximum increase of 35.5 degreesC in the degradation temperature was displayed by these nanocomposites. Additionally, the surface elastic modulus and hardness of these nanocomposites were more than double those of pure polystyrene. (C) 2004 Wiley Periodicals, Inc.
Thickness dependence of current conduction and carrier distribution of GaAsN grown on GaAs
(2005-10-01)
Chen, JF
;
Hsiao, RS
;
Hsieh, MT
;
Huang, WD
;
Guo, PS
Thickness dependence of the properties of GaAsN grown on GaAs was investigated by characterizing GaAs/GaAS(0.982)N(0.018)/ GaAs Schottky diodes by current-voltage (I-V), capacitance-voltage (C-V) profiling and deep-level transient spectroscopy (DLTS). I-V characteristics show a considerable increase in the saturation current when the GaAsN thickness is increased from 60 to 250 A. As GaAsN thickness is increased further, the I-V characteristic deviates from that of a normal Schottky diode with a large series resistance. These I-V characteristics correlate well with carrier distribution. In thick GaAsN samples, C-V profiling shows carrier depletion in the top GaAs layer and frequency-dispersion accumulation in the GaAsN layer. DLTS spectra show that the carrier depletion in the top GaAs layer is due to an EL2 trap and the frequency-dispersion accumulation is due to the removal of electrons from a trap at 0.35 eV in the GaAsN layer. Increasing the GaAsN thickness markedly increases the magnitude of both traps. The large series resistance in thick GaAsN samples is due to EL2 that markedly depletes the top GaAs layer.