Browsing by Author "Hong, Y. -L."

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Carrier dynamics of Mg-doped indium nitride
(2010-08-09)
Ahn, H.
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Yu, K. -J.
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Hong, Y. -L.
;
Gwo, S.
;
光電工程學系
Recently, we have reported a significant enhancement (>500 times in intensity) in terahertz emission from Mg-doped indium nitride (InN:Mg) films compared to undoped InN. It was found that the intensity of terahertz radiation strongly depends on the background electron density. In this letter, we present the results on ultrafast time-resolved reflectivity measurement employed to investigate the carrier dynamics of InN:Mg. We find that the decay time constant of InN:Mg depends on background electron density in the same way as terahertz radiation does. The spatial redistribution of carriers in diffusion and drift is found to be responsible for the recombination behavior as well as terahertz radiation. (C) 2010 American Institute of Physics. [doi:10.1063/1.3479523]
Carrier dynamics of Mg-doped indium nitride
(2011)
Ahn, H.
;
Hong, C. -C.
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Hong, Y. -L.
;
Gwo, S.
;
光電工程學系
We report the carrier density dependence of carrier dynamics of Mg-doped InN (InN:Mg) films. Recently, we have demonstrated a significant enhancement of terahertz emission from InN: Mg, which is due to the temporal evolution of drift and diffusion currents depending on the background carrier density. We studied the details of carrier dynamics of InN: Mg which is crucial for the clarification of the terahertz emission mechanism by performing the time-resolved optical reflectivity measurement on InN: Mg films grown with different Mg-doping levels. Experimental analysis demonstrates that the initial sharp drop and recovery of reflectivity response of InN: Mg films are dominated by photocarrier-dependent bandgap renormalization and band filling processes, whereas the slow decay time constant (tau(2)) of reflectivity of InN: Mg has the strong dependence on the background carrier density. As the carrier density decreases from that of undoped InN, tau(2) of InN: Mg continuously increases and reaches the maximum value at a critical value of similar to 1x10(18) cm(-3). Interestingly, the strongest terahertz radiation was observed at this carrier density and it keeps decreasing with the increase of carrier density. Intense terahertz radiation corresponds to the fast and large spatial separation of charged carrier density through diffusion and drift. Large spatial separation results in the longer decay time for charged carriers to reach equilibrium after strong emission of terahertz waves, and it explains the similar carrier density dependence of terahertz emission and tau(2).
Intense terahertz emission from a-plane InN surface
(2008-03-10)
Ahn, H.
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Ku, Y. -P.
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Chuang, C. -H.
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Pan, C. -L.
;
Lin, H. -W.
We report a significant enhancement in terahertz emission from the indium nitride (InN) films grown along the a axis (a-plane InN), relative to the InN films grown along the c axis. The primary radiation mechanism of the a-plane InN film is found to be due to the acceleration of photoexcited carriers under the polarization-induced in-plane electric field perpendicular to the a axis, which effectively enhances the geometrical coupling of the radiation out of semiconductor. In addition, azimuthal angle dependence measurement shows that the p-polarized terahertz output consists of a large angularly independent component and a weak component with a distinctive fourfold rotation symmetry. (c) 2008 American Institute of Physics.
Mg-induced terahertz transparency of indium nitride films
(2011-12-05)
Ahn, H.
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Chia, J. -W.
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Lee, H. -M.
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Hong, Y. -L.
;
Gwo, S.
Terahertz time-domain spectroscopy (THz-TDS) has been used to investigate electrical properties of Mg-doped indium nitride (InN). Mg-doping in InN was found to significantly increase terahertz transmittance. THz-TDS analysis based on the Drude model shows that this high transmittance from Mg-doped InN is mainly due to the reduction in mobility associated with ionized dopants. The Hall-effect-measured mobility is typically lower than the THz-TDS-measured mobility for the same samples. However, the results of both measurements have the same slope in the linear relation between mobility and density. By introducing a compensation ratio of similar to 0.2, an excellent agreement in mobilities of two methods is obtained. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3669538]
Terahertz emission mechanism of magnesium doped indium nitride
(2009-12-07)
Ahn, H.
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Yeh, Y. -J.
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Hong, Y. -L.
;
Gwo, S.
;
光電工程學系
We report carrier concentration-dependence of terahertz emission from magnesium doped indium nitride (InN:Mg) films. Near the critical concentration (n(c) similar to 1 x 10(18) cm(-3)), the competition between two emission mechanisms determines the polarity of terahertz emission. InN: Mg with n > n(c) exhibits enhanced positive polarity terahertz emission compared to the undoped InN, which is due to the reduced screening of the photo-Dember field. For InN: Mg with n < n(c), the polarity of terahertz signal changes to negative, indicating the dominant contribution of the surface electric field due to the large downward surface band bending within the surface layer extending over the optical absorption depth. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3270042]
Terahertz Emission of Magnesium doped Indiu
(2010)
Yeh, Y. -J.
;
Ahn, H.
;
Hong, Y. -L.
;
Gwo, Shangjr
;
光電工程學系
Significant THz power enhancement and polarity reversal were observed from Mg-doped InN. The carrier concentration-dependent THz polarity reversal reflects the interplay between the surface-electric-field and the photo-Dember field for THz emission from InN:Mg. (C)2010 Optical Society of America
Terahertz Emission of Magnesium doped Indium Nitride
(2010)
Yeh, Y. -J.
;
Ahn, H.
;
Hong, Y. -L.
;
Gwo, Shangjr
;
光電工程學系
Significant THz power enhancement and polarity reversal were observed from Mg-doped InN. The carrier concentration-dependent THz polarity reversal reflects the interplay between the surface-electric-field and the photo-Dember field for THz emission from InN:Mg. (C)2010 Optical Society of America