Browsing by Author "Lee, Ling"

Now showing 1 - 12 of 12

Cathodoluminescence studies of GaAs nano-wires grown on shallow-trench-patterned Si
(2010-11-19)
Lee, Ling
;
Fan, Wen-Chung
;
Ku, Jui-Tai
;
Chang, Wen-Hao
;
Chen, Wei-Kuo
The optical properties of GaAs nano-wires grown on shallow-trench-patterned Si(001) substrates were investigated by cathodoluminescence. The results showed that when the trench width ranges from 80 to 100 nm, the emission efficiency of GaAs can be enhanced and is stronger than that of a homogeneously grown epilayer. The suppression of non-radiative centers is attributed to the trapping of both threading dislocations and planar defects at the trench sidewalls. This approach demonstrates the feasibility of growing nano-scaled GaAs-based optoelectronic devices on Si substrates.
Cathodoluminescence studies of GaAs nano-wires grown on shallow-trench-patterned Si
(2010-11-19)
Lee, Ling
;
Fan, Wen-Chung
;
Ku, Jui-Tai
;
Chang, Wen-Hao
;
Chen, Wei-Kuo
The optical properties of GaAs nano-wires grown on shallow-trench-patterned Si(001) substrates were investigated by cathodoluminescence. The results showed that when the trench width ranges from 80 to 100 nm, the emission efficiency of GaAs can be enhanced and is stronger than that of a homogeneously grown epilayer. The suppression of non-radiative centers is attributed to the trapping of both threading dislocations and planar defects at the trench sidewalls. This approach demonstrates the feasibility of growing nano-scaled GaAs-based optoelectronic devices on Si substrates.
Environmentally and Mechanically Stable Selenium 1D/2D Hybrid Structures for Broad-Range Photoresponse from Ultraviolet to Infrared Wavelengths
(2018-10-17)
Chen, Yu-Ze
;
You, Yen-Ting
;
Chen, Pin Jung
;
Li, Dapan
;
Su, Teng-Yu
Selenium (Se) is one of the potential candidates as photodetector because of its outstanding properties such as high photoconductivity (similar to 8 x 10(4) S cm(-1)), piezoelectricity, thermoelectricity, and nonlinear optical responses. Solution phase synthesis becomes an efficient way to produce Se, but a contamination issue that could deteriorate the electric characteristic of Se should be taken into account. In this work, a facile, controllable approach of synthesizing Se nanowires (NWs)/films via a plasma-assisted growth process was demonstrated at the low substrate temperature of 100 degrees C. The detailed formation mechanisms of nanowires arrays to thin films at different plasma powers were investigated. Moreover, indium (In) layer was used to enhance the adhesive strength with 50% improvement on a SiO2/Si substrate by mechanical interlocking and surface alloying between Se and In layers, indicating great tolerance for mechanical stress for future wearable devices applications. Furthermore, the direct growth of Se NWs/films on a poly(ethylene terephthalate) substrate was demonstrated, exhibiting a visible to broad infrared detection ranges from 405 to 1555 nm with a high on/off ratio of similar to 700 as well as the fast response time less than 25 ms. In addition, the devices exhibited fascinating stability in the atmosphere over one month.
Growth evolution and magneto-optical characteristics of self-assembled ZnTe/ZnMnSe quantum dots
(2013-09-01)
Lee, Ling
;
Fan, Wen-Chung
;
Chien, Kun-Feng
;
Tzou, An-Jye
;
Chou, Wu-Ching
The growth evolution and the magneto-optical characteristics of the self-assembled single-layer ZnTe/ZnMnSe quantum dots grown by molecular beam epitaxy were investigated. As the ZnTe coverage is above 2.0 monolayers, a Stranski-Krastanov growth process is observed with a significantly increased dot density on top of two-dimensional plateaus. As the coverage exceeds 2.7 monolayers, ripened dots dominate instead. Furthermore, a saturated degree of circular polarization of 76% at applied magnetic field of 4 T and the formation of magnetic polarons with a formation time of 7.4 ns were demonstrated. (c) 2012 Elsevier B.V. All rights reserved.
Improvement of defect reduction in semi-polar GaN grown on shallow-trenched Si(001) substrate
(2012)
Lee, Ling
;
Chien, Kun-Feng
;
Chou, Wu-Ching
;
Ko, Chih-Hsin
;
Wu, Cheng-Hsien
The improved design of sub-micron trenches on Si(001) substrate was demonstrated for defect suppression in semi-polar selectively-grown GaN layers. Cathodoluminescence and transmission electron microscopy measurements revealed a dramatically decreased density of threading dislocations and stacking faults near the surface of the overgrown GaN layer when the trench width ranged from 500 to 1500 nm. It was observed that defects were effectively trapped inside the trench when the ratio of trench depth to the SiO2 thickness is less than 0.66. In addition, a significant reduction of intrinsic polarization electric field was achieved for the InGaN/GaN multiple quantum well on the GaN selectively grown from the Si trenches.
Integrating SIP and IEEE 802.11e to support handoff and multi-grade QoS for VoIP-over-WLAN applications
(2011-06-01)
Chen, Jen-Jee
;
Lee, Ling
;
Tseng, Yu-Chee
;
資訊工程學系
;
Department of Computer Science
With the increasing popularity of WLANs and the growing demand for VoIP services, there is a need to guarantee QoS for VoIP calls while support as many calls as possible. Prior efforts focus on call admission control (CAC), but did not address the important handoff and physical rate adaptation issues caused by mobility and wireless channel variation. Assuming that VoIP calls can be supported by multi-grade QoS levels and that handoff and rate adaptation are possible, we show how to conduct CAC and resource management by integrating SIP and the QoS mechanisms of IEEE 802.11e together. When wireless resource is stringent, our resource management can dynamically adjust the resource distribution among existing calls by controlling their supporting codecs and packetization intervals. This not only takes care of calls in bad channel conditions, but also can accept more calls. Thus multi-grade QoS is achieved with decreased blocking rate for new calls and less dropping rate for handoff calls. In addition, we also show how to achieve early resumption of resources for handoff calls. Both analytical and simulation results are presented to evaluate the performance of the proposed schemes. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.
Optical Properties of Uncapped InN Nanodots Grown at Various Temperatures
(2009-03-01)
Chen, Ching-Yu
;
Lee, Ling
;
Tai, Shin-Kai
;
Fu, Shao-Fu
;
Ke, Wen-Cheng
Photoluminescence (PL) measurements were employed to investigate the emission properties of uncapped InN nanodot samples grown at temperature from 550 to 725 degrees C. Our results indicate that once the In droplets are formed, the optical properties of InN dots deteriorate markedly. As for those droplet-free samples grown at temperatures >= 600 degrees C, good luminescence properties are obtained. The corresponding 20 K PL peak energy is found to be almost constant at approximately 0.77 eV with a slow increase in its linewidth from 71 to 74 meV. A strong temperature-induced energy blue shift at approximately 20 to 280 K is considered to be partially connected to the band-filling effects of thermally stimulated surface electrons. (C) 2009 The Japan Society of Applied Physics
Optical Studies of GaAs Nanowires Grown on Trenched Si(001) Substrate by Cathodoluminescence
(2012-06-01)
Lee, Ling
;
Chien, Kun-Feng
;
Fan, Wen-Chung
;
Chou, Wu-Ching
;
Ko, Chih-Hsin
"The strains in GaAs nanowires, which were grown from 1700- to 80-nm-wide trenches on the Si(001) wafer with SiO2 masks, were investigated by cathodoluminescence. For 1700- to 500-nm-wide trenches, the in-plane tensile strain at 15 K decreases with the decreasing trench width. The strain increases abruptly when the trench width is 300 nm, and then decreases as the trench width is further decreased. The results revealed that the stress induced by the SiO2 sidewalls dominates when the width is less than the depth of the trench. This approach provides an effective technique to measure the strain of a single nanowire and helps for the demonstration of selectively-grown GaAs with a designed strain. (C) 2012 The Japan Society of Applied Physics"
Origin of localized states in zinc-blende ZnCdSe thin films and the influence on carrier relaxation of self-assembled ZnTe/ZnCdSe quantum dots
(2015-05-25)
Lee, Ling
;
Dai, Yue-Ru
;
Yang, Chu-Shou
;
Fan, Wen-Chung
;
Chou, Wu-Ching
This study discovered the origin of deep level emission in zinc-blende ZnCdSe thin films grown by molecular beam epitaxy, in which a localization behavior was noticed. Pronounced deep level emission observed in films grown under a VI/II ratio of 1.74 (Se-accumulated regime) could be suppressed by a lower VI/II ratio of 1.04 (intermediate regime) and 0.74 (metal-rich regime). Hence the localized states could be correlated to excess selenium accumulated at the growth surface. The localized states also influence the carrier relaxation process of self-assembled ZnTe quantum dots embedded in a ZnCdSe matrix. Once quantum dots surmount the wetting layer, localized electrons in the capping layer dominate the type-II transition and exhibit size-independent lifetimes. (C) 2015 Elsevier B.V. All rights reserved.
Scratch Characteristics of ZnMgO Epilayers
(2015-05-01)
Wen, Hua-Chiang
;
Chou, Wu-Ching
;
Chiang, Tun-Yuan
;
Fan, Wen-Chung
;
Lee, Ling
Zn0.75Mg0.25O films were grown via metal organic vapor phase epitaxy on an M-plane sapphire substrate. We used nanoscratch tests to study the abrasive plow of the films; comparable cases of critical pileup were obtained on both sides of each scratch when the ramped load increased from 0 to 250 mu N. The film showed a crack in the bulge edge between the groove at ramped loads of 1000 mu N as well as full plastic deformation. The values of mu were 0.14, 0.33, 0.43, and 0.48 for the ramped loads of 250 mu N and 0.22, 0.26, 0.28, and 0.33 for the ramped load of 1000 mu N. We found that cracking dominated in the case of Zn0.75Mg0.25O films during plowing. Lower values of the coefficient of friction and shallower penetration depths were observed at RT, while higher values were observed in the annealed samples. It is suggested that higher growth temperatures induce lower bonding forces and reduce the shear resistances of Zn-0.75Mg0.25O films.
Study of extending carrier lifetime in ZnTe quantum dots coupled with ZnCdSe quantum well
(2018-03-01)
Fan, W. C.
;
Chou, W. C.
;
Lee, J. D.
;
Lee, Ling
;
Nguyen Dang Phu
We demonstrated the growth of a self-assembled type-II ZnTe/ZnSe quantum dot (QD) structure coupled with a type-I Zn0.88Cd0.12Se/ZnSe quantum well (QW) on the (001) GaAs substrate by molecular beam epitaxy (MBE). As the spacer thickness is less than 2 nm, the carrier lifetime increasing from 20 ns to nearly 200 ns was successfully achieved. By utilizing the time-resolved photoluminescence (TRPL) and PL with different excitation power, we identify the PL emission from the coupled QDs consisting of two recombination mechanisms. One is the recombination between electrons in ZnSe barrier and holes confined within ZnTe QDs, and the other is between electrons confined in Zn0.88Cd0.12Se QW and holes confined within ZnTe QDs. According to the band diagram and power-dependent PL, both of the two recombinations reveal the type-II transition. In addition, the second recombination mechanism dominates the whole carrier recombination as the spacer thickness is less than 2 nm. A significant extension of carrier lifetime by increasing the electron and hole separation is illustrated in a type-II ZnTe/ZnSe QD structure coupling with a type-I ZnCdSe/ZnSe QW. Current sample structure could be used to increase the quantum efficient of solar cell based on the II-VI compound semiconductors.
Using nanoindentation and cathodoluminescence to investigate the residual stress of ZnSe
(2015-03-15)
Wen, Hua-Chiang
;
Chou, Wu-Ching
;
Yau, Wei-Hung
;
Fan, Wen-Chung
;
Lee, Ling
In this study we examined the effects of the nanoindentation-induced residual stress of single-crystalline zinc selenide (ZnSe). We employed the nanoindentation technique to evaluate the dislocation mobility of ZnSe at loading ratios of 10 and 2 mN/min, with a holding time of 120 s under a constant load. We visualized the resultant dislocation and microcracks using cathodoluminescence (CL) spectroscopy and mapping to compare the nanoindentation-induced residual stresses of the various ZnSe samples. CL mapping revealed massive dislocation activities during the loading process. The dislocations played roles as nonradiative recombination centers that quenched the local CL intensity. Transmission electron microscopy also revealed the effects of nanoindentation-induced residual stress. To obtain insight into the influence of the residual stress and to determine the dislocation mobilities for ZnSe films, it was essential to monitor the quenching effect of nonradiative recombination centers as a function of CL mapping. (C) 2014 Elsevier B.V. All rights reserved.