Browsing by Author "Lee, Ming-Chih"

Now showing 1 - 13 of 13

Carrier dynamics of type-II InAs/GaAs quantum dots covered by a thin GaAs(1-x)Sb(x) layer
(2008-07-21)
Chang, Wen-Hao
;
Liao, Yu-An
;
Hsu, Wei-Ting
;
Lee, Ming-Chih
;
Chiu, Pei-Chin
Carrier dynamics of InAs/GaAs quantum dots (QDs) covered by a thin GaAs(1-x)Sb(x) layer were investigated by time-resolved photoluminescence (PL). Both the power dependence of PL peak shift and the long decay time constants confirm the type-II band alignment at the GaAsSb-InAs interface. Different recombination paths have been clarified by temperature dependent measurements. At lower temperatures, the long-range recombination between the QD electrons and the holes trapped by localized states in the GaAsSb layer is important, resulting in a non-single-exponential decay. At higher temperatures, optical transitions are dominated by the short-range recombination with the holes confined to the band-bending region surrounding the QDs. (C) 2008 American Institute of Physics.
Current properties of GaNV-defect using conductive atomic force microscopy
(2006-08-01)
Lee, Lino
;
Ku, Ching-Shun
;
Ke, Wen-Cheng
;
Ho, Chih-Wei
;
Huang, Huai-Ying
Current conduction behavior on GaN V-defect was studied comprehensively using conductive atomic force microscopy. Experimental results indicate that the forward current in the V-defect region is at least three-order higher than that at surrounding area. On the other hand, a snowflake-like leakage current pattern was observed in the V-defect owing to the ease of current breakdown at the crest lines and perimeters. Further static current-voltage measurement suggests that the current flow is governed by Schottky emission and Fowler-Nordheim tunneling for V-defect region and surrounding area, respectively.
Diamagnetic Response of Exciton Complexes in Semiconductor Quantum Dots
(2008-12-31)
Tsai, Ming-Fu
;
Lin, Hsuan
;
Lin, Chia-Hsien
;
Lin, Sheng-Di
;
Wang, Sheng-Yun
We report measurements of diamagnetic shifts for different exciton complexes confined in small InAs quantum dots. The measured diamagnetic responses are sensitive to the number of carriers in the exciton complexes, with systematic differences between neutral excitons, biexcitons, and trions. Theoretical calculations suggest that such systematic differences arise from very different extents of electron and hole wave functions confined in small quantum dots. The measured magnetic response of Coulomb energies is found to vary with the cube of the wave function extent, and can be a sensitive probe to the electron-hole wave function asymmetry.
Effects of growth temperature on InN/GaN nanodots grown by metal organic chemical vapor deposition
(2008-05-15)
Chang, Wen-Hao
;
Ke, Wen-Cheng
;
Yu, Shu-Hung
;
Lee, Lin
;
Chen, Ching-Yu
InN nanodots grown on GaN by metal organic chemical vapor deposition using conventional growth mode as well as flow-rate modulation epitaxy at various growth temperatures (550-730 degrees C) were investigated. We found that different precursor injection schemes together with the effect of growth temperatures greatly influenced the surface morphology of InN nanodots and their photoluminescence (PL) properties. The sample grown at around 650 degrees C showed the highest growth rate. For samples grown at higher temperatures, the residual carrier concentration was reduced and the PL efficiency was improved. Furthermore, we found that the growth of InN nanodots is still sustainable even at a temperature higher than 700 degrees C while retaining their optical quality. (c) 2008 American Institute of Physics.
Exciton fine structures and energy transfer in single InGaAs quantum-dot molecules
(2009)
Lin, Hsuan
;
Wang, Sheng-Yun
;
Lin, Chia-Hsien
;
Chang, Wen-Hao
;
Cheng, Shun-Jen
We present a spectroscopic study of single quantum-dot molecules (QDMs) formed by two closely stacked In(0.5)Ga(0.5)As/GaAs layers. It was found that the interdot coupling and directional energy transfer between the two adjacent dots can be controlled by temperature tuning. Direct and indirect excitons, as well as charged excitons in single QDMs were classified and identified by excitation-power dependent, excitation-energy dependent and polarization-resolved microphotoluminescence measurements. With the increasing temperature, the direct-exciton intensity decreases while the indirect-exciton intensity increases. A rate equation model considering phonon mediated processes has been developed. The directional energy transfer in QDMs is explained in terms of the phonon-assisted tunnelling of hole between the two adjacent dots. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Nonresonant carrier transfer in single InGaAs/GaAs quantum dot molecules
(2008-06-01)
Chang, Wen-Hao
;
Lin, Hsuan
;
Wang, Sheng-Yun
;
Lin, Chia-Hsien
;
Cheng, Shun-Jen
We present a spectroscopic study of single quantum dot molecules (QDMs) formed by two closely stacked In(0.5)Ga(0.5)As layers. The exciton fine structures as well as direct and indirect excitonic species associated with QDMs were identified by power dependent and polarization resolved microphotoluminescence measurements. As the temperature was increased, a directional energy transfer between the direct and indirect excitons in single QDMs was observed. A rate-equation model was developed to explain our data. We show that a phonon-assisted nonresonant tunneling of the hole between the two adjacent dots is responsible for such directional energy transfers in QDMs.
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
Process for manufacturing self-assembled nanoparticles
(2006-02-09)
Chen, Wei-Kuo
;
Lee, Ming-Chih
;
Chou, Wu-Ching
;
Chen, Wen-Hsiung
;
Ke, Wen-Cheng
Process for fabricating self-assembled nanoparticles on buffer layers without mask making and allowing for any degree of lattice mismatch; that is, binary, ternary or quaternary nanoparticles comprising Groups III-V, II-VI or IV-VI. The process includes a first step of applying a buffer layer, a second step of turning on the purge gas to modulate the first reactant to the lower first flow rate, then the second reactant is supplied to the buffer layer to form a metal-rich island on the buffer layer, and a third step of turning on purge gas again to modulate the first reactant to the higher second flow rate onto the buffer layer. On the metal-rich island is formed the nanoparticles of the binary, ternary or quaternary III-V, II-VI and IV-IV semiconductor material. This is then recrystallized under the first reactant flow at high temperature forming high quality nanoparticles.
Size-dependent strain relaxation in InN islands grown on GaN by metalorganic chemical vapor deposition
(2009-02-09)
Tsai, Wen-Che
;
Lin, Feng-Yi
;
Ke, Wen-Cheng
;
Lu, Shu-Kai
;
Cheng, Shun-Jen
We report Raman measurements on InN islands grown on GaN by metalorganic chemical vapor deposition. The Raman frequency of the InN E(2) mode is found to decrease exponentially with the island's aspect ratio, indicating a size dependent strain relaxation during the island formation. Our results suggest that most of the strain at the InN-GaN interface have been released plastically during the initial stage of island formations. After that, the residual strain of only -3.5x10(-3) is further relaxed elastically via surface islanding. The experimental data are in agreement with the strain relaxation predicted from a simplified model analysis as well as three-dimensional finite-element simulations.
Structural and optical properties of In-rich InGaN nanodots grown by metallo-organic chemical vapor deposition
(2007-10-10)
Tsai, Wen-Che
;
Lin, Hsuan
;
Ke, Wen-Chen
;
Chang, Wen-Hao
;
Chou, Wu-Ching
The surface morphologies, alloy compositions and emission properties of In- rich InxGa1-xN nanodots ( x >= 0.87) grown by metallo-organic chemical vapor deposition at various growth temperatures (550-750 degrees C) were investigated. We found that the nucleation of InGaN dots was dominated by the surface migration of In adatoms. A higher Ga content can be achieved at lower growth temperatures due to the relatively lower migration ability of Ga adatoms. At higher growth temperatures, the InGaN dots tend to decompose into In- rich islands and a thin Ga-rich layer. These In- rich islands exhibit photoluminescence emission in the near-infrared range. Another visible emission band was also observed for samples grown at higher temperatures. The formation of a thin Ga-rich layer is likely to be responsible for the visible emission.
Structural and optical properties of indium-rich InGaN islands
(2008)
Tsai, Wen-Che
;
Lin, Hsuan
;
Ke, Wen-Chen
;
Chang, Wen-Hao
;
Chou, Wu-Ching
Indium-rich InxGa1-xN islands (x >= 0.87) grown by metalor-ganic chemical vapor deposition at growth temperatures ranging from 550-750 degrees C were investigated. With the increasing growth temperature, the InGaN dot size increases while the dot density decreases due to the enhanced surface migration of In/Ga adatoms at elevated temperatures. In addition, the compositiom of InGaN-islands was also found to be varied with the growth temperature. At lower growth temperatures, a higher Ga content can be achieved due to the relatively lower migration ability of Ga adatoms. At higher growth temperatures, the deposited InGaN material tend to decompose into In-rich islands and a thin Ga-rich layer, Photoluminescence investigations show that these In-rich islands exhibit a near-infrared emission band . For samples grown at higher temperatures a visible emission band was also observed. The visible emission band may arise from defect hands introduced during the formation of Ga-rich InGaN layer. (c) 2008 WILEY-VCH Veriag GmbH & Co. KGaA, Weinheim.
Structural and optical properties of InN/GaN nanodots grown by metalorganic chemical vapor deposition
(2008)
Chang, Wen-Hao
;
Lee, Lin
;
Chen, Ching-Yu
;
Tsai, Wen-Che
;
Lin, Hsuan
InN nanodots grown on GaN by metalorganic chemical vapor deposition (MOCVD) using conventional growth mode as well as flow-rate modulation epitaxy (FME) at various growth temperatures (550-730 degrees C) were investigated. We found that different precursor injection schemes together with the effect of growth temperatures greatly influenced the surface morphology of InN dots and their photoluminescence (PL) properties. The best growth efficiency of InN was achieved by FME at around 650 degrees C. The residual carrier concentration and PL efficiency was also be improved when a high growth temperature was used. Our results indicated that InN nanodots can be grown at a temperature even higher than 700 degrees C while maintain their optical quality. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Time-resolved photoluminescence of type-II InAs/GaAs quantum dots covered by a thin GaAs(1-x)Sb(x) layer
(2009)
Liao, Yu-An
;
Hsu, Wei-Ting
;
Lee, Ming-Chih
;
Chiu, Pei-Chin
;
Chyi, Jen-Inn
We investigate carrier lifetimes of InAs/GaAs quantum dots (QDs) covered by a thin GaAs(1-x)Sb(x) layer by time-resolved photoluminescence (PL). Both the power dependent PL peak shift and the longer decay time confirm the type-II band alignments. Different recombination paths have been identified by temperature dependent measurements. At low temperatures, the long-range recombination with holes trapped in the GaAsSb layer is significant, resulting in non-single-exponential decays. The short-range recombination with holes confined in the band-bending region surrounding the InAs QDs is important at higher temperatures. The variation in decay time across the ground-state and the temporal PL peak redshift further confirm the localization of holes in the GaAsSb layer. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim