Browsing by Author "Kechiantz, A"

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Subwavelength gratings fabricated on semiconductor substrates via E-beam lithography and lift-off method
(2005-03-01)
Sun, KW
;
Huang, SC
;
Kechiantz, A
;
Lee, CP
;
電子工程學系及電子研究所
We present results of the fabrication and measurements on reflective polarizers consisting of stacked bi-layer subwavelength metal gratings prepared on GaAs (100) substrates. These linear gratings were fabricated using electron-beam direct-writing lithography and the lift-off method with periods less than the wavelength of light used for measurements. At normal incidence, the polarizer reflects the light polarized perpendicular to the grating lines (transverse magnetic polarization, TM polarized) but absorbs parallel-polarized light (transverse electric polarization, TE polarized). By optimizing structural parameters, the polarization extinction ratio close to 20 has been experimentally achieved at wavelength of 650 run.
Ultrafast carrier capture and relaxation in modulation-doped InAs quantum dots
(2006-04-17)
Sun, KW
;
Kechiantz, A
;
Lee, BC
;
Lee, CP
;
應用化學系
We report investigations on carrier capture and relaxation processes in undoped and modulation-doped InAs/GaAs self-assembled quantum dots (QDs) by using time-resolved spectroscopy technique with a time resolution of similar to 200 fs. We find that carrier capture and relaxation in the ground state of the charged QD are faster compared to the undoped dots even at an excitation level as low as 1x10(10) cm(-2). It is attributed to the triggering of the vibrating polarization field induced by the presence of cold carriers in the doped dots. The rate of an electron been captured by a positively charged QD is also calculated based on our proposed model. (c) 2006 American Institute of Physics.