Browsing by Author "Chou, Rone-Hwa"

Now showing 1 - 3 of 3

Analysis of terahertz pulses from large-aperture biased semi-insulating and arsenic-ion-implanted GaAs antennas
(2008-09-01)
Chou, Rone-Hwa
;
Liu, Tze-An
;
Pan, Ci-Ling
;
光電工程學系
;
Department of Photonics
We investigate the characteristics of terahertz radiation pulses generated using biased semi-insulating and arsenic-ion-implanted GaAs photoconductive antennas with 1.5 cm aperture size under various pump fluences and bias fields. Compared with semi-insulating GaAs antenna, our arsenic-ion-implanted GaAs antenna exhibits larger bandwidth and better emission efficiency. Our simulation verifies that the superior characteristics for the latter can be partly attributed to larger optical absorption in the ion-implanted layer. For both types of antennas, we observe that the radiated peak terahertz amplitude displays an anomalous dependence on pump fluence, which deviates from the prediction given by the scaling rule. Analyzing the theoretical and simulation results, we infer that this behavior arises from band filling and two-photon absorption effects. At specific pump fluence, we find that the dependence of peak terahertz amplitude on bias field is distinct from the usual linear relationship predicted by the scaling rule. (c) 2008 American Institute of Physics.
Gap-Dependent Terahertz Pulses from Mid-Size-Gap Multi-Energy Arsenic-Ion-Implanted GaAs Antennas
(2008-11-01)
Chou, Rone-Hwa
;
Pan, Ci-Ling
;
光電工程學系
;
Department of Photonics
We investigated the characteristics of sub-picosecond radiation pulses from mid-size-gap multi-energy arsenic-ion-implanted GaAs photoconductive antennas in terahertz time-domain spectroscopy experiments. At fixed fluence excitation, both the bandwidth and the negative peak of terahertz waveform minimum reveal increasing trends with increases in the antenna's gap. We reproduce both the measured terahertz waveforms and increasing trends numerically, by calculating a model that incorporates the trap-enhanced bias field with wave equation. We deduce from our simulation that the gap-dependent behavior stems from the fact that an antenna with a larger gap has a stronger trap-enhanced bias field near the anode edge and thereby induces a larger space-charge screening effect and bandwidth. [DOI: 10.1143/JJAP.47.8419]
Phonon thermal conductivity suppression of bulk silicon nanowire composites for efficient thermoelectric conversion
(2010-09-13)
Chen, Ting-Gang
;
Yu, Peichen
;
Chou, Rone-Hwa
;
Pan, Ci-Ling
;
光電工程學系
Vertically-aligned silicon nanowires (SiNWs) that demonstrate reductions of phonon thermal conductivities are ideal components for thermoelectric devices. In this paper, we present large-area silicon nanowire arrays in various lengths using a silver-induced, electroless-etching method that is applicable to both n- and p-type substrates. The measured thermal conductivities of nanowire composites are significantly reduced by up to 43%, compared to that of bulk silicon. Detailed calculations based on the series thermal resistance and phonon radiative transfer models confirm the reduction of thermal conductivity not only due to the increased air fraction, but also the nanowire size effect, suggesting the soundness of employing bulk silicon nanowire composites as efficient thermoelectric materials. (C) 2010 Optical Society of America