Browsing by Author "Suen, Y. W."

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Correlated Electric Fluctuations in GaN Nanowire Devices
(2009-02-01)
Li, L. C.
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Huang, S. Y.
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Wei, J. A.
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Suen, Y. W.
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Lee, M. W.
We report an experimental study on the correlation spectrums between different sections of a multicontact GaN nanowire device. Our results indicate that there exists a negative correlation between the voltage fluctuations of adjacent sections of the nanowire separated by a metal contact in the transition region between the low-frequency 1/f noise and the high-frequency white thermal noise. We suggest that this correlation is caused by the voltage fluctuation under the contact area.
Edge magnetoplasma excitations in quantum wire arrays
(2008-03-01)
Hsieh, W. H.
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Suen, Y. W.
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Lee, B. C.
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Li, L. C.
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Lee, C. P.
We report the low-temperature microwave properties of edge magneto-plasma excitations in quantum-wire arrays, fabricated from a two-dimensional electron gas in a GaAs/AlGaAs heterostructure and embedded in the slots of a 50-Omega meandering coplanar waveguide. The plot of frequency versus Landau level filling factors with strong absorption gives a series of barn-shaped curves with tops being centered in the quantum Hall effect plateaus and following a straight line through the origin. Away from the plateau center, the absorption dip becomes weaker and disappears near the plateau-plateau transition regime, qualitatively following the magneto hydrodynamic model. At frequencies above this barn-shaped part, however, we also observed unexpected resonant dips. (c) 2007 Published by Elsevier B.V.
Electrical characteristics of Ni Ohmic contact on n-type GeSn
(2014-06-16)
Li, H.
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Cheng, H. H.
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Lee, L. C.
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Lee, C. P.
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Su, L. H.
We report an investigation of the electrical and material characteristics of Ni on an n-type GeSn film under thermal annealing. The current-voltage traces measured with the transmission line method are linear for a wide range of annealing temperatures. The specific contact resistivity was found to decrease with increasing annealing temperature, followed by an increase as the annealing temperature further increased, with a minimum value at an annealing temperature of 350 degrees C. The material characteristics at the interface layer were measured by energy-dispersive spectrometer, showing that an atomic ratio of (Ni)/(GeSn) = 1:1 yields the lowest specific contact resistivity. (C) 2014 AIP Publishing LLC.
Electron delocalization of tensily strained GaAs quantum dots in GaSb matrix
(2010-12-15)
Lin, T. C.
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Wu, Y. H.
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Li, L. C.
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Sung, Y. T.
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Lin, S. D.
The magneto-optical response of type-II tensily strained GaAs self-assembled quantum dots in GaSb was investigated in magnetic fields up to 14 T. By depositing different GaAs amount, the dot sizes and the corresponding emission energies were varied. We analyzed the carrier wave function extent of different dots using the diamagnetic shift results. It was found that, with the increase in the energy (the reduction in the dot size), the diamagnetic coefficient first rises quickly and then saturates at around 21 mu eV/T(2). Based on a simple calculation model, this unusual tendency is attributed to the electrons gradually spilling out of the quantum dot to the wetting layer as the dots get smaller. This delocalization effect is enhanced in this material system due to the tensile strain relaxation within the dots, which raises the conduction band edge over that in the wetting layer. (c) 2010 American Institute of Physics. [doi: 10.1063/1.3520669]
Low-Frequency Noise Characterization of CoFeB/MgO/CoFeB MTJ-Based Perpendicular Field Sensor
(2016-07)
Das, Bipul
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Lee, Y. C.
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Li, L. C.
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Yi-Shiou, Liu
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Suen, Y. W.
We report low-frequency electrical resistance noise of Co40Fe40B20/MgO/Co20Fe60B20-based magnetic tunnel junction field sensors with reference and sensing layer magnetization directions along the out-of-plane and in-plane directions, respectively. The devices are fabricated using the sputter deposition and conventional lithography techniques with a short axis of similar to 6 mu m long and long axes of similar to 6-12 mu m long. Noise power spectra under different bias currents indicate increase in noise power with increasing bias current. A close 1/ f dependence of the noise according to Hooge\'s relation, S-V (f) = AV(2)/f(alpha) (A is Hooge\'s like constant) is observed with an average value of alpha = 1.03 +/- 0.08. In smaller devices, the magnetic field dependence of noise amplitude follows similar trend of magnetoresistance (MR) behavior without any distinct peak near antiparallel-parallel states transition of the devices, which is generally observed for magnetic defects-induced resistance fluctuation. The experimental observations infer the resistance noises in those devices that are related to the defects associated with the spin independent charge trapping at structural defects near or in the barrier layer. The device with the smallest lateral size exhibits the Lorentzian contribution, whereas the device with the largest size shows magnetic contribution in total noise. Numerically deduced magnetic fluctuations Delta B-rms of all the devices shows an average magnetic fluctuation of similar to 10 nT except for one device. The devices show the highest MR% of similar to 27% under perpendicular magnetic field with a dynamic range of similar to +/- 25 Oe and a sensitivity of similar to 0.3%/Oe. The observed low-frequency noise levels are suitable for the perpendicular field detection application and can be reduced more by improving the crystallinity of the device films stacks and their interfaces.
Low-Frequency Noise Characterization of CoFeB/MgO/CoFeB MTJ-Based Perpendicular Field Sensor
(2016-07-01)
Das, Bipul
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Lee, Y. C.
;
Li, L. C.
;
Yi-Shiou, Liu
;
Suen, Y. W.
We report low-frequency electrical resistance noise of Co40Fe40B20/MgO/Co20Fe60B20-based magnetic tunnel junction field sensors with reference and sensing layer magnetization directions along the out-of-plane and in-plane directions, respectively. The devices are fabricated using the sputter deposition and conventional lithography techniques with a short axis of similar to 6 mu m long and long axes of similar to 6-12 mu m long. Noise power spectra under different bias currents indicate increase in noise power with increasing bias current. A close 1/ f dependence of the noise according to Hooge's relation, S-V (f) = AV(2)/f(alpha) (A is Hooge's like constant) is observed with an average value of alpha = 1.03 +/- 0.08. In smaller devices, the magnetic field dependence of noise amplitude follows similar trend of magnetoresistance (MR) behavior without any distinct peak near antiparallel-parallel states transition of the devices, which is generally observed for magnetic defects-induced resistance fluctuation. The experimental observations infer the resistance noises in those devices that are related to the defects associated with the spin independent charge trapping at structural defects near or in the barrier layer. The device with the smallest lateral size exhibits the Lorentzian contribution, whereas the device with the largest size shows magnetic contribution in total noise. Numerically deduced magnetic fluctuations Delta B-rms of all the devices shows an average magnetic fluctuation of similar to 10 nT except for one device. The devices show the highest MR% of similar to 27% under perpendicular magnetic field with a dynamic range of similar to +/- 25 Oe and a sensitivity of similar to 0.3%/Oe. The observed low-frequency noise levels are suitable for the perpendicular field detection application and can be reduced more by improving the crystallinity of the device films stacks and their interfaces.
Magnetic tunnel junction based out-of-plane field sensor with perpendicular magnetic anisotropy in reference layer
(2015-05-07)
Lee, Y. C.
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Chao, C. T.
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Li, L. C.
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Suen, Y. W.
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Horng, Lance
A magnetic tunnel junction (MTJ) with orthogonal magnetic anisotropy and consisting of Ta X/Co40Fe40B20 1.2 (reference)/MgO 2.0/Co20Fe60B20 2.3 (sensing)/Ta 5/Ru 5 (thickness in nanometers), where X ranges from 15 to 30, is proposed and investigated in response to the demand for out-of-plane field sensors. The reference layer with perpendicular magnetic anisotropy (PMA) demonstrates tuneable coercivity ranging from 72 Oe to 175 Oe. The sensing layer exhibits in-plane anisotropy with the avoidance of exchange coupling from the PMA reference layer because of a thick MgO barrier layer. The magnetization reversal behavior of micron scale devices not only corresponds well to the sheet film, but is also independent in terms of shape and size. The magnetoresistance curve exhibits a ratio of similar to 27% in the presence of a perpendicular field and is insensitive to the in-plane field. For perpendicular field sensing, the dynamic range with a sensitivity of similar to 0.3%/Oe can achieve +/- 25 Oe with a coercive field of less than 3 Oe. Additionally, even when bias is applied up to 9.1 mV, magnetic fluctuation still stays below 0.15 mOe. (C) 2015 AIP Publishing LLC.
Magnetophotoluminescence properties of Co-doped ZnO nanorods
(2009-04-13)
Lin, C. Y.
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Wang, W. H.
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Lee, C. -S.
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Sun, K. W.
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Suen, Y. W.
We present the detailed experimental results of the magnetic and optical properties of cobalt doped ZnO nanorods, especially the temperature and magnetic field dependence of photoluminescence up to 14 T. The Raman measurements indicate that our Co-doped ZnO nanorods have the same lattice constant as crystalline bulk ZnO. Sharp luminescence peaks centered at around 670 nm were observed at low temperature and their intensity decreased with increasing magnetic field. The luminescence peaks were attributed to d-d transitions in the Ligand field from the doped Co ions. We also observed a diamagnetic shift at a temperature of 1.5 K when the magnetic field was scanned from 0 to 14 T. The exciton radius of the Co-doped ZnO nanorods was deduced from the magnetophotoluminescence results.
Microwave-induced DC currents in mesoscopic structures
(2010-02-01)
Li, L. C.
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Sung, Y. T.
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Chang, C. W.
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Suen, Y. W.
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Chen, K. Y.
We report the power (P) dependence of microwave (MW)-induced current (I(ph)) of a 1-mu m sized mesoscopic structure fabricated from two-dimensional electron gas in the GaAs/AlGaAs heterostructure at temperature of 1.4 K. MW signals were fed onto the sample through a loop antenna nearby and I(ph) is measured from a pair of ohmic contacts. We found that I(ph) is proportional to P at low-P limit; this dependence has been predicted for diffusion-limited electron transport in mesoscopic systems. By contrast, for large P. the dependence is extremely non-monotonous and complicated; even though its physical origin is still not clear so far, our data suggest it is related to the scattering processes from boundaries and impurities in the mesoscopic structure. We also investigated the symmetry properties against reversal of magnetic field (B) and found that the field-symmetric part of I(ph)(B) is consistent with the variation of magnetoresistance; there exists also an anti-symmetric part, which should be related to time-reversal-symmetry-breaking scattering mechanisms in the channel. (C) 2009 Elsevier B.V. All rights reserved.
Mobility asymmetry in InGaAs/InAlAs heterostructures with InAs quantum wires
(2007-02-21)
Lin, Z. C.
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Hsieh, W. H.
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Lee, C. P.
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Suen, Y. W.
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電子工程學系及電子研究所
Strong asymmetry of electron mobility in InGaAs/InAlAs heterostructures (lattice matched to InP) with the presence of InAs quantum wires was observed. Self-assembled InAs quantum wires, embedded in an InGaAs matrix close to the hetero-interface, has a strong effect in electron conduction in the interface channel. The low temperature mobility for electrons moving parallel to the quantum wires is much higher than that of electrons moving perpendicular to the wires. The asymmetry in mobility is attributed to the difference in scattering cross section of the quantum wires in these two directions.
Temperature dependence of the excess noise of a GaN nanowire device
(2007)
Li, L. C.
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Huang, S. Y.
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Wei, J. A.
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Suen, Y. W.
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Lee, M. W.
We report on the study of the low-frequency excess noise of a GaN nanowire (NW) device from room temperature to 135 K. A Lorentzian noise is found to be embedded in the 1/f noise background, and becomes more significant as the bias current increases or the temperature decreases. The temperature dependance of the associated characteristic time, extracted from the spectrum, shows two thermally activated regions with different activation energies, which originate from different carrier-trapping levels in the NW device. The temperature dependence of the 1/f noise is difficult to unveil due to the presence of the strong Lorentzian noise.