Browsing by Author "Wu, Jau-Yang"

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A delta-doped quantum well system with additional modulation doping
(2011)
Luo, Dong-Sheng
;
Lin, Li-Hung
;
Su, Yi-Chun
;
Wang, Yi-Ting
;
Peng, Zai Fong
A delta-doped quantum well with additional modulation doping may have potential applications. Utilizing such a hybrid system, it is possible to experimentally realize an extremely high two-dimensional electron gas (2DEG) density without suffering inter-electronic-subband scattering. In this article, the authors report on transport measurements on a delta-doped quantum well system with extra modulation doping. We have observed a 0-10 direct insulator-quantum Hall (I-QH) transition where the numbers 0 and 10 correspond to the insulator and Landau level filling factor nu = 10 QH state, respectively. In situ titled-magnetic field measurements reveal that the observed direct I-QH transition depends on the magnetic component perpendicular to the quantum well, and the electron system within this structure is 2D in nature. Furthermore, transport measurements on the 2DEG of this study show that carrier density, resistance and mobility are approximately temperature (T)-independent over a wide range of T. Such results could be an advantage for applications in T-insensitive devices.
Characterization of Single-Crystalline Aluminum Thin Film on (100) GaAs Substrate
(2013-04-01)
Lin, Shi-Wei
;
Wu, Jau-Yang
;
Lin, Sheng-Di
;
Lo, Ming-Cheng
;
Lin, Ming-Huei
We have studied the structure and physical properties of an aluminum thin film grown on a (100) GaAs substrate. The X-ray diffraction (XRD) data shows that the Al film grown in situ by molecular beam epitaxy (MBE) is single crystalline. Compared with the polycrystalline film ex situ evaporated using an electron-gun (E-gun), the MBE-grown Al film has a high optical reflectivity in the visible and ultraviolet (UV) regime. In addition, the MBE-grown film has a 2-order-lower residue resistance, a 1-order-higher temperature coefficient of resistance, and a 2-order-larger magnetoresistance (MR) than the polycrystalline film. Owing to the long mean free time, the bulk-like electron-to-hole transition of Hall resistivity is observed for the first time in a nanoscale metal thin film. Our results suggest that MBE-grown Al thin films have great potential applications in metal-based nanoelectronics and nanophotonics. (C) 2013 The Japan Society of Applied Physics
Constant Excess Bias Control for Single-Photon Avalanche Diode Using Real-Time Breakdown Monitoring
(2015-08-01)
Chang, Po-Hsuan
;
Tsai, Chia-Ming
;
Wu, Jau-Yang
;
Lin, Sheng-Di
;
Kuo, Ming-Ching
A monolithic constant excess bias control circuit for single-photon avalanche diode (SPAD) in standard 0.18-mu m CMOS technology is reported. The proposed real-time breakdown monitoring technique is incorporated into a passive-quenching-active-reset circuit. A sample-and-hold circuit samples the breakdown level of SPAD through well-defined sampling phase. Following the sample-and-hold circuit, the level shifter with voltage shifting defined by predetermined excess bias provides the reset voltage of SPAD. The design operates the SPAD under constant excess bias and effectively mitigates the impact of the process-voltage-temperature variation by maintaining the optimal excess bias condition.
Enhanced Phase Relaxation in a Hybrid Ferromagnet/Semiconductor System
(2009-07-01)
Chen, Kuang Yao
;
Yang, Chun-Kai
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Liang, C. -T.
;
Aoki, N.
;
Ochiai, Y.
Hybrid ferromagnet/semiconductor systems have been the focus of considerable attention because of the transport properties of two-dimensional electron systems and their potential applications to magnetic storage and sensing devices. We use the weak localization effect to probe the dephasing mechanism at low temperatures. In our study, the zero-temperature phase-relaxation rate can be enhanced in a hybrid ferromagnet/semiconductor system, which may he due to the inhomogeneous magnetic field emanating from the Ni film. The result may improve understanding of the issue of zero-temperature dephasing in disordered systems.
Huge positive magnetoresistance in a gated AlGaAs/GaAs high electron mobility transistor structure at high temperatures
(2008-03-31)
Liang, C. -T.
;
Tseng, Yen Shung
;
Wu, Jau-Yang
;
Lin, Sheng-Di
;
Yang, Chun-Kai
Magnetoresistivity measurements on a gated AlGaAs/GaAs high electron mobility transistor (HEMT) structure were performed at high temperatures T. By changing the applied gate voltage V(g), we can investigate the observed huge positive magnetoresistance (PMR) at different effective disorder and density inhomogeneity within the same HEMT structure. The observed PMR value increases with increasing disorder in the depletion mode (V(g)<= 0). Moreover, the PMR value is not limited by the quality of the HEMT structure at T=80 K. Such results pave the way for low-cost, high-throughput GaAs-based HEMT fabrication for future magnetic sensing and recording devices fully compatible with the mature HEMT technology. (C) 2008 American Institute of Physics.
Lateral Two-Dimensional p-i-n Diode in a Completely Undoped GaAs/AlGaAs Quantum Well
(2013-01-01)
Van-Truong Dai
;
Lin, Sheng-Di
;
Lin, Shih-Wei
;
Wu, Jau-Yang
;
Li, Liang-Chen
A lateral two-dimensional p-i-n junction in an entirely undoped GaAs/AlGaAs quantum well has been fabricated. The optical and electrical characteristics of the junction are reported. The threshold voltage of the junction and the electroluminescence spectrum of the quantum well confirm the formation of the lateral two-dimensional junction. (C) 2013 The Japan Society of Applied Physics
Low temperature and high magnetic field spectroscopic ellipsometry system
(2014-05-01)
Su, Sheng-Kai
;
Li, Liang-Chen
;
Suen, Yuen-Wuu
;
Wu, Jau-Yang
;
Kuo, Hong-Rong
We report on the design and implementation of a spectral ellipsometer at near-infrared wavelength (700-1000 nm) for samples placed in high magnetic fields (up to 14 T) at low temperatures (similar to 4.2 K). The main optical components are integrated in a probe, which can be inserted into a conventional long-neck He dewar and has a very long free-space optical path (similar to 1.8 mx2). A polarizer-sample-(quarter-wave plate)-rotating analyzer configuration was employed. Two dielectric mirrors, one before and one after the sample in the optical path, helped to reflect the light back to the analyzer and a two-axis piezo-driven goniometer under the sample holder was used to control the direction of the reflected light. Functional test results performed on an intrinsic GaAs wafer and analysis on the random error of the system are shown. We obtained both amplitude and phase ellipsometric spectra simultaneously and observed helicity transformation at energies near the GaAs exciton transitions in the phase spectra. Significant shifts of them induced by magnetic fields were observed and fitted with a simple model. This system will allow us to study the collective magneto-optical response of materials and spatial dispersive exciton-polariton related problems in high external magnetic fields at low temperatures. (C) 2014 AIP Publishing LLC.
Low temperature and high magnetic field spectroscopic ellipsometry system
(2014-05-01)
Su, Sheng-Kai
;
Li, Liang-Chen
;
Suen, Yuen-Wuu
;
Wu, Jau-Yang
;
Kuo, Hong-Rong
We report on the design and implementation of a spectral ellipsometer at near-infrared wavelength (700-1000 nm) for samples placed in high magnetic fields (up to 14 T) at low temperatures (similar to 4.2 K). The main optical components are integrated in a probe, which can be inserted into a conventional long-neck He dewar and has a very long free-space optical path (similar to 1.8 mx2). A polarizer-sample-(quarter-wave plate)-rotating analyzer configuration was employed. Two dielectric mirrors, one before and one after the sample in the optical path, helped to reflect the light back to the analyzer and a two-axis piezo-driven goniometer under the sample holder was used to control the direction of the reflected light. Functional test results performed on an intrinsic GaAs wafer and analysis on the random error of the system are shown. We obtained both amplitude and phase ellipsometric spectra simultaneously and observed helicity transformation at energies near the GaAs exciton transitions in the phase spectra. Significant shifts of them induced by magnetic fields were observed and fitted with a simple model. This system will allow us to study the collective magneto-optical response of materials and spatial dispersive exciton-polariton related problems in high external magnetic fields at low temperatures. (C) 2014 AIP Publishing LLC.
Low-noise single-photon avalanche diodes in 0.25 mu m high-voltage CMOS technology
(2013-01-01)
Hsu, Fang-Ze
;
Wu, Jau-Yang
;
Lin, Sheng-Di
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
By using 0.25 mu m high-voltage CMOS technology, we have designed and fabricated a structure of single-photon detectors. The new single-photon avalanche diode (SPAD) has (to our knowledge) the lowest dark count rate per unit area at room temperature without any technology customization. Our design is promising for realizing low-cost and high-performance SPAD arrays for imaging applications. (C) 2012 Optical Society of America
Magnetotransport in an aluminum thin film on a GaAs substrate grown by molecular beam epitaxy
(2011)
Lo, Shun-Tsung
;
Chuang, Chiashain
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Lin, Sheng-Di
;
Chen, Kuang Yao
;
Liang, Chi-Te
Magnetotransport measurements are performed on an aluminum thin film grown on a GaAs substrate. A crossover from electron- to hole-dominant transport can be inferred from both longitudinal resistivity and Hall resistivity with increasing the perpendicular magnetic field B. Also, phenomena of localization effects can be seen at low B. By analyzing the zero-field resistivity as a function of temperature T, we show the importance of surface scattering in such a nanoscale film.
Method to evaluate afterpulsing probability in single-photon avalanche diodes
(2015-08-15)
Tzou, Bo-Wei
;
Wu, Jau-Yang
;
Lee, Yi-Shan
;
Lin, Sheng-Di
;
電機工程學系
We propose and demonstrate a new method for evaluating the afterpulsing effect in single-photon avalanche photodiodes (SPADs). By analyzing the statistical property of dark count rate, we can quantitatively characterize afterpulsing probability (APP) of a SPAD. In experiment, the temperature-dependent low dark count rate (DCR) distribution becomes non-Poissonian at lower temperature and has higher excess bias as the afterpulsing effect becomes significant. Our work provides a flexible way to examine APP in either single-device or circuit level. (C) 2015 Optical Society of America
Probing Insulator-quantum Hall Transitions by Current Heating
(2009-07-01)
Chen, Kuang Yao
;
Liang, C. -T.
;
Aoki, N.
;
Ochiai, Y.
;
Cheng, K. A.
We report a magneto-transport study on the two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure. The direct insulator to quantum Hall conductor transition is observed at low temperatures by increasing the magnetic field B perpendicular to the 2DES. We can also observe the transition by varying the current I and find a relation T(e) similar to I(a) between electron effective temperature T(e) and current. Here, a denotes the exponent for the power law. The exponent a, however, can have different values on the two sides of the transition point, which indicates different inelastic scattering mechanisms in the low-field insulator and in the quantum Hall conductor.
Probing Landau quantization with the presence of insulator-quantum Hall transition in a GaAs two-dimensional electron system
(2008-07-23)
Chen, Kuang Yao
;
Chang, Y. H.
;
Liang, C-T
;
Aoki, N.
;
Ochiai, Y.
Magneto-transport measurements are performed on the two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure. By increasing the magnetic field perpendicular to the 2DES, magneto-resistivity oscillations due to Landau quantization can be identified just near the direct insulator-quantum Hall (I-QH) transition. However, different mobilities are obtained from the oscillations and transition point. Our study shows that the direct I-QH transition does not always correspond to the onset of strong localization.
Probing mobility gaps at resistivity minima in the integer quantum Hall effect
(2008)
Liang, C. -T.
;
Chen, K. Y.
;
Wu, Jau-Yang
;
Lin, S. D.
;
Lin, Li-Hung
Magneto-transport measurements are performed on the AlGaAs/GaAs quantum Hall (QH) devices fabricated recently by our group. A series of Hall plateaus are observed with increasing the perpendicular magnetic field, and the mobility gaps resulting from localization effects are investigated at the minima in the longitudinal resistivity. Only the gap corresponding to the filling factor i=2 is close to the expected cyclotron energy, and our study supports that the low-field QH conductors may suffer problems due to insufficient localization. The anomalous change on the Hall slope is observed when the i=3 plateau is destroyed by the large current.
SIMULATION OF ELECTRIC FIELD DISTRIBUTION IN CMOS SINGLE PHOTON AVALANCHE DIODES AT BREAKDOWN VOLTAGE
(2014-01-01)
Wu, Jau-Yang
;
Lin, Sheng-Di
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We simulate the electric field distribution in single-photon avalanche diodes (SPADs) fabricated by CMOS 0.25-mu m high-voltage technology to explain the observed non-uniform 2-D photo-count mapping. The cause of non-uniform electric field distribution at the breakdown voltage is discussed with the aid of simulation. A method for improving the electric field uniformity is also proposed accordingly.
Single-Crystalline Aluminum Nanostructures on a Semiconducting GaAs Substrate for Ultraviolet to Near-Infrared Plasmonics
(2015-04-01)
Liu, Hsuan-Wei
;
Lin, Fan-Cheng
;
Lin, Shi-Wei
;
Wu, Jau-Yang
;
Chou, Bo-Tsun
Aluminum, as a metallic material for plasmonics, is of great interest because it extends the applications of surface plasmon resonance into the ultraviolet (UV) region and is superior to noble metals in natural abundance, cost, and compatibility with modern semiconductor fabrication processes. Ultrasmooth single-crystalline metallic films are beneficial for the fabrication of high-definition plasmonic nanostructures, especially complex integrated nanocircuits. The absence of surface corrugation and crystal boundaries also guarantees superior optical properties and applications in nanolasers. Here, we present UV to near-infrared plasmonic resonance of single-crystalline aluminum nanoslits and nanoholes. The high-definition nanostructures are fabricated with focused ion-beam milling into an ultrasmooth single-crystalline aluminum film grown on a semiconducting GaAs substrate with a molecular beam epitaxy method. The single-crystalline aluminum film shows improved reflectivity and reduced two-photon photoluminescence (TPPL) due to the ultrasmooth surface. Both linear scattering and nonlinear TPPL are studied in detail. The nanoslit arrays show clear Fano-like resonance, and the nanoholes are found to support both photonic modes and localized surface plasmon resonance. We also found that TPPL generation is more efficient when the excitation polarization is parallel rather than perpendicular to the edge of the aluminum film. Such a counterintuitive phenomenon is attributed to the high refractive index of the GaAs substrate. We show that the polarization of TPPL from aluminum preserves the excitation polarization and is independent of the crystal orientation of the film or substrate. Our study gains insight into the optical property of aluminum nanostructures on a high-index semiconducting GaAs substrate and illustrates a practical route to implement plasmonic devices onto semiconductors for future hybrid nanodevices.
Two-dimensional photo-mapping on CMOS single-photon avalanche diodes
(2014-06-30)
Wu, Jau-Yang
;
Lu, Ping-Keng
;
Lin, Sheng-Di
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Two-dimensional (2-D) photo-count mapping on CMOS single photon avalanche diodes (SPADs) has been demonstrated. Together with the varied incident wavelengths, the depth-dependent electric field distribution in active region has been investigated on two SPADs with different structures. Clear but different non-uniformity of photo-response have been observed for the two studied devices. With the help of simulation tool, the non-uniform photo-counts arising from the electric field non-uniformity have been well explained. As the quasi-3D distribution of electric field in the active region can be mapped, our method is useful for engineering the device structure to improve the photo-response of SPADs. (C) 2014 Optical Society of America