Browsing by Author "Chen, Shu-Han"

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Characterization and Comparison of GaAs/AlGaAs Uni-Traveling Carrier and Separated-Transport-Recombination Photodiode Based High-Power Sub-THz Photonic Transmitters
(2010-01-01)
Li, Yu-Tai
;
Shi, Jin-Wei
;
Huang, C. -Y.
;
Chen, Nan-Wei
;
Chen, Shu-Han
We describe in detail the characterization of two high-power photonic transmitters based on two different kinds of high-power photodiodes, one a GaAs/AlGaAs based uni-traveling-carrier photodiode (UTC-PD) and the other a separated-transport-recombination photodiode (STR-PD). The diodes operate under optical pulse excitation at the 800 nm wavelength. Both PDs have the same total depletion layer thickness (same theoretical RC-limited bandwidth) and are m integrated with the same broadband micro-machined circular disk monopole antennas to radiate strong sub-THz pulses. However the STR-PD based transmitter exhibits very different dynamic and static performance from that of the UTC-PD based transmitter due to the existence of a low-temperature-grown GaAs (LTG-GaAs) based recombination center inside the active region, and the much thinner thickness of effective depletion layer. Under optical pulse excitation (similar to 480 pJ/pulse), the STR-PD based transmitter exhibits a much lower maximum averaged output photocurrent (1.2 mA versus 0.3 mA) than that of the UTC-PD transmitter, although the radiated electrical pulse-width and maximum peak-power, which are measured by the same THz time-domain spectroscopic (TDS) system, of both devices are comparable. These results indicate that although the recombination center in the STR-PD degrades its DC responsivity, it effectively improves the high-speed and output power performance of the device and eliminates the DC component of the photocurrent, which should minimize device-heating problem during high-power operation. The radiated waveforms of both devices under intense optical pulse illumination also exhibit excellent linearity and strong bias dependent magnitude. This suggests their suitability for application as photonic emitters and possibly as a data modulator in sub-THz impulse-radio communication systems.
Characterization of sub-THz photonic-transmitters based on CaAs-AlGaAs uni-traveling-carrier photodiodes and substrate-removed broadband antennas for impulse-radio communication
(2008-07-01)
Li, Yu-Tai
;
Shi, J. -W.
;
Huang, Cheng-Yu
;
Chen, Nan-Wei
;
Chen, Shu-Han
A novel photonic transmitter for wireless terahertz (THz) impulse-radio (IR) communication is realized by monolithic integration of a GaAs-AlGaAs-based uni-traveling-carrier (UTC) photodiode with a substrate-removed broadband antenna. The device can radiate strong sub-THz pulses (20-mW peak-power) with a narrow pulsewidth (< 2 ps) and wide bandwidth (100 similar to 250 GHz). The maximum average power emitted by our device, under the same THz time-domain spectroscopic setup, is around ten times higher than that of the low-temperature-grown GaAs-based photoconductive antenna, while with a much lower dc bias (9 versus 35 V). The bias-dependent peak output powers of our devices suggest their suitability for application as a data modulator/emitter for photonic THz IR communication.
DC Characteristics of InAlAs/InGaAsSb/InGaAs Double Heterojunction Bipolar Transistors
(2010-12-01)
Chen, Shu-Han
;
Chang, Chao-Min
;
Chiang, Pei-Yi
;
Wang, Sheng-Yu
;
Chang, Wen-Hao
DC electrical characteristics of a series of InAlAs/InGaAsSb/InGaAs double heterojunction bipolar transistors (DHBTs) that are grown on InP by molecular beam epitaxy are reported and analyzed. The InGaAsSb base of the transistors leads to a type-I base-emitter junction and a type-II base-collector junction, resulting in unique device characteristics, such as low turn-on voltage, low crossover current, and constant current gain over a wide current range. In addition, the DHBTs exhibit rather high current gains despite the use of a heavily doped thick InGaAsSb base layer. This indicates the long minority carrier lifetime of the InGaAsSb material. A high current gain over base sheet resistance ratio is, thus, realized with these novel DHBTs.
Graphitic carbon film formation under Ni templates by radio-frequency sputtering for transparent electrode applications
(2011-11-01)
Lin, Meng-Yu
;
Sheng, Yung-Shuan
;
Chen, Shu-Han
;
Su, Ching-Yuan
;
Li, Lain-Jong
An alternate approach to the preparation of transfer-free graphitic carbon films is proposed in this paper. Using a standard radio-frequency sputtering system and a high-temperature annealing procedure, graphitic carbon films are prepared under Ni templates. The results demonstrate that carbon precipitation occurs at both Ni template interfaces. With repeated annealing procedures at 1100 degrees C, a sheet resistance of 1.36 x 10(4) Omega/square can be achieved. Selective carbon film deposition has also been developed via pattern formation on the Ni templates. The results indicate the potential application of this method to transparent electrode formation. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3646481]
In-Plane Gate Transistors Fabricated by Using Atomic Force Microscopy Anode Oxidation
(2010-11-01)
Chung, Tung-Hsun
;
Chen, Shu-Han
;
Liao, Wen-Hsuan
;
Lin, Shih-Yen
;
光電工程學系
An in-plane gate transistor fabricated by using the atomic force microscopy (AFM) lithography is investigated in this letter. By performing repeated oxidation and deoxidation procedures by using the AFM for four times, two V-shaped trenches are fabricated on the prepatterned mesas to isolate the electrical terminals of the device. Without exposing the channel region to the atmosphere, the device has exhibited standard transistor current-voltage characteristics in the 0-5 V range at room temperature, which may be advantageous for the future high-speed application of the device.
Influence of As on the Morphologies and Optical Characteristics of GaSb/GaAs Quantum Dots
(2011-03-01)
Tseng, Chi-Che
;
Mai, Shu-Cheng
;
Lin, Wei-Hsun
;
Wu, Shung-Yi
;
Yu, Bang-Ying
The influence of As atoms on the morphologies of GaSb quantum dots (QDs) is investigated. Without any special treatment, GaSb quantum rings (QRs) are observed in the embedded GaSb layer even when the uncapped layer reveals QD-like morphologies. With intentional As supply after the uncapped GaSb QD deposition, a QD to QR transition is observed. The phenomenon suggests that insufficient Sb atoms on the GaSb QDs would lead to the QD to QR transition as in the case of embedded GaSb layers. With extended Sb soaking time following GaSb deposition, QD structures could be well maintained for the embedded GaSb layers. A light-emitting diode operated at room temperature is fabricated based on the GaSb/GaAs QD structure. Identical peak positions in photoluminescence and electroluminescence (EL) spectra of the device show that type-II GaSb QDs are responsible for the observed EL.
Room-temperature operation type-II GaSb/GaAs quantum-dot infrared light-emitting diode
(2010-03-22)
Lin, Shih-Yen
;
Tseng, Chi-Che
;
Lin, Wei-Hsun
;
Mai, Shu-Cheng
;
Wu, Shung-Yi
A GaSb/GaAs quantum-dot light-emitting diode (QD LED) with a single GaSb QD layer is investigated in this paper. The room-temperature photoluminescence peak blueshift with increasing excitation power densities suggests a type-II alignment of the GaSb/GaAs heterostructures. Significant electroluminescence (EL) is observed for the device under forward biases, which suggests that pronounced dipole transitions occur at the GaSb/GaAs interfaces. With increasing forward biases, the observed EL peak blueshift confirms that the origin of luminescence is from the type-II GaSb/GaAs QD structures. A model is established to explain the operation mechanisms of the type-II QD LED.
Site-controlled self-assembled InAs quantum dots grown on GaAs substrates
(2010-07-23)
Lin, Shih-Yen
;
Tseng, Chi-Che
;
Chung, Tung-Hsun
;
Liao, Wen-Hsuan
;
Chen, Shu-Han
Atomically-flat surfaces are obtained after thin GaAsSb buffer layer growth on GaAs substrates with regular-distributed nano-holes formed after oxide desorption of the local atomic-force-microscopy anode oxidation. Different from the samples with GaAsSb buffer layers, increasing surface root-mean-square roughness is observed for the GaAs-buffered samples with increasing GaAs buffer layer thickness. The phenomenon is attributed to the enhanced adatom migration resulting from the incorporation of Sb atoms. By using the substrates with nano-holes after buffer layer growth, site-controlled self-assembled InAs quantum dots (QDs) are observed with the deposition of a below-critical-thickness InAs coverage of 1.3 monolayer (ML).
Sub-THz Photonic-Transmitters Based on GaAs/AlGaAs Uni-Traveling Carrier Photodiode and Micromachined Circular Disk Monopole Antenna for Ultra-wideband Communication
(2008)
Li, Yu-Tai
;
Pan, Ci-Ling
;
Shi, J. -W.
;
Huang, Cheng-Yu
;
Chen, Nan-Wei
By incorporating GaAs/AlGaAs based uni-traveling-carrier photodiodes with broadband micromachined monopole antennas, the demonstrated photonic-transmitter can radiate strong sub-THz pulses (20mW peak-power) with a wide bandwidth (100 similar to 250GHz), which was measured by another photonic-receiver for ultra-wideband communication. (c) 2008 Optical Society of America
The transition mechanisms of type-II GaSb/GaAs quantum-dot infrared light-emitting diodes
(2011-05-15)
Tseng, Chi-Che
;
Lin, Wei-Hsun
;
Wu, Shung-Yi
;
Chen, Shu-Han
;
Lin, Shih-Yen
The light-emitting diode (LED) with a single GaSb QD layer embedded in a GaAs n-i-p structure operated under different injection currents and temperatures is investigated. With increase in injection currents, room-temperature electroluminescence (EL) peak blue shift is observed until a saturation of EL intensity is reached. In the temperature-varying EL measurements, with increase in temperatures. EL peak blue shift and then red shift are observed, which is attributed to the enhanced luminescence of the smaller QDs with increase in temperatures lower than 100 K. The understanding of the operation mechanisms for the device is advantageous for the practical application of type-II LEDs. (C) 2010 Elsevier B.V. All rights reserved.