Browsing by Author "Lee, BC"

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Carrier capture and relaxation in InAs quantum dots
(2005-09-01)
Sun, KW
;
Chen, JW
;
Lee, BC
;
Lee, CP
;
Kechiantz, AM
We have investigated the carrier capture and relaxation processes in InAs/GaAs self-assembled quantum dots at room temperature by time-resolved photoluminescence techniques with a high time resolution of similar to 200 fs. Following the initial fast relaxation in GaAs barriers, we have observed rising processes in time-resolved PL intensity at the energies of quantum dot confined states and the wetting layer. The rising processes are assigned to the carrier capture from the barriers into the wetting layer and confined states in InAs dots and subsequent relaxation in each detected energy level. We found that the carrier capture rate is faster than the intra-dot relaxation within the range of excitation densities that we investigated. Under high excitation intensity, the electronic states in the dots were populated mainly by carriers directly captured from the barrier. However, at low excitation densities, the PL rise times were influenced by the carrier diffusion.
Formation of semiconductor quantum rings using GaAs/AlAs partially capped layers
(2004-07-01)
Lee, BC
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A new method for fabricating semiconductor quantum rings has been developed. Instead of using the conventional GaAs cap layer, we used the GaAs/AlAs cap layer for the ring formation. The additional AlAs layer impedes the inward diffusion of the Ga and Al atoms and results in nicely formed ring structures with a more relaxed growth condition. Because of this layer, the ring-shaped structure can be maintained with a higher annealing temperature without being washed out by the intermixing of Ga/Al with In in the central region of the dots. The shape and the strain distribution of quantum rings have also been characterized by transmission electron microscopy.
High-sensitivity microwave vector detection at extremely low-power levels for low-dimensional electron systems
(2004-11-01)
Hsieh, WH
;
Kuan, CH
;
Suen, YW
;
Chang, SY
;
Li, LC
We present a high-sensitivity microwave vector detection system for studying the low-dimensional electron system embedded in the gaps of a coplanar waveguide at low temperatures. Using this system, we have achieved 0.005% and 0.001degrees resolutions in amplitude and phase variations, respectively, at 10 GHz in a magnetotransport measurement on a quantum-wire array with an average signal power less than -75 dBm into the sample at 0.3 K. From the measured phase variation, we can distinguish a very tiny change in the induced dipole moment of each quantum wire. (C) 2004 American Institute of Physics.
III-V semiconductor nano-rings
(2004-08-01)
Lee, BC
;
Voskoboynikov, O
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this work, we briefly review present day knowledge about possible types, methods of fabrication, and fascination physical properties of nano-scale semiconductor rings. In particular, we discuss models of the ring formation, energetic, magnetic, and magneto-optical properties of InAs/GaAs and InAs/InP nano-rings as well as GaAs/GaSb "open nanorings". In addition, we summarize results of realistic theoretical -simulations of the electronic energy spectra, magnetic and optical properties for totally three-dimensional models of nano-scale quantum rings. (C) 2004 Elsevier B.V. All rights reserved.
Improvement of near-ultraviolet InGaN/GaN light-emitting diodes by inserting an in situ rough SiN(x) interlayer in n-GaN layers
(2003-10-27)
Tu, RC
;
Chuo, CC
;
Pan, SM
;
Fan, YM
;
Tsai, CE
Near-ultraviolet 400-nm InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with and without an in situ rough SiN(x) interlayer inserted into the n-GaN underlying layer were grown on c-face sapphire substrates by metalorganic vapor phase epitaxy. Inserting the SiN(x) interlayer into the n-GaN underlying layer slightly reduced leakage current induced by reducing the defect density. Additionally, an enhancement of light extraction for the LED with a SiN(x) interlayer is expected because of the increased intensity of light scattered on the SiN(x) nanomask, changing the directions of propagation of light. Consequently, the emission efficiency of an LED with an in situ rough SiN(x) interlayer doubles that without a SiN(x) interlayer. (C) 2003 American Institute of Physics.
Improvement of near-ultraviolet InGaN/GaN light-emitting diodes by inserting an in situ rough SiNx interlayer in n-GaN layers
(2003-10-27)
Tu, RC
;
Chuo, CC
;
Pan, SM
;
Fan, YM
;
Tsai, CE
Near-ultraviolet 400-nm InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with and without an in situ rough SiNx interlayer inserted into the n-GaN underlying layer were grown on c-face sapphire substrates by metalorganic vapor phase epitaxy. Inserting the SiNx interlayer into the n-GaN underlying layer slightly reduced leakage current induced by reducing the defect density. Additionally, an enhancement of light extraction for the LED with a SiNx interlayer is expected because of the increased intensity of light scattered on the SiNx nanomask, changing the directions of propagation of light. Consequently, the emission efficiency of an LED with an in situ rough SiNx interlayer doubles that without a SiNx interlayer. (C) 2003 American Institute of Physics.
Molecular beam epitaxial growth and photoluminescence studies of InAs self-organized quantum dots on patterned GaAs (001) substrates
(2001)
Lee, BC
;
Lee, HM
;
Wu, JC
;
Chang, YP
;
Sun, KW
We present experimental results on the growth of InAs self-organized quantum dots on patterned substrates via molecular beam epitaxy. Luminescence spectra of these quantum dots have been studied.
Selective growth and photoluminescence studies of InAs self-organized quantum dot arrays on patterned GaAs(001) substrates
(2002-10-01)
Sun, KW
;
Wu, JC
;
Lee, BC
;
Lee, CP
;
電子工程學系及電子研究所
In this paper, we present experimental results oil the selective growth of InAs self-organized quantum dots on patterned substrates using electron-beam lithography and molecular beam epitaxy. Higher dot densities were found on the patterned substrate with a particular pattern orientation compared to the densities of dots grown on the non-patterned area. Good quality of the quantum dot arrays and long-range ordering was also achieved. We have also studied the luminescence spectra of these quantum dots. Dots grown on patterned substrates do indeed show different luminescence characteristics compared to dots on non-patterned surfaces. (Some figures in this article are in colour only in the electronic version).
Selective growth of single InAs quantum dots using strain engineering
(2002-01-14)
Lee, BC
;
Lin, SD
;
Lee, CP
;
Lee, HM
;
Wu, JC
A method to achieve ordering and selective positioning of single InAs self-assembled quantum dots (QDs) has been developed. The selective growth was achieved by manipulating the strain distribution on the sample surface. The QDs are formed on predesigned mesas with added strain. Single dots were obtained on small mesas. Using this technique, two-dimensional single QD arrays have been achieved. (C) 2002 American Institute of Physics.
Ultra-high-density InGaN quantum dots grown by metalorganic chemical vapor deposition
(2004-02-15)
Tu, RC
;
Tun, CJ
;
Chuo, CC
;
Lee, BC
;
Tsai, CE
This study examined how the duration of SiNx treatment on an underlying GaN layer affects the optical property, surface morphology and density of following InGaN quantum dots (QDs). InGaN QDs with extremely high density of near 3 x 10(11) cm(-2) exhibited strong photoluminescence (PL) emission at room temperature (RT). Increasing the duration of the SiN, treatment of the underlying GaN layer, the RT-PL peak of the following InGaN nano-islands and QDs was found to be red-shifted from the violet to the greenish region, and the spectrum was broadened. Additionally, the average height of InGaN nano-islands and QDs increased with the duration of SiNs treatment, explaining the redshift of the RT-PL peak.
Ultrafast carrier capture and relaxation in modulation-doped InAs quantum dots
(2006-04-17)
Sun, KW
;
Kechiantz, A
;
Lee, BC
;
Lee, CP
;
應用化學系
We report investigations on carrier capture and relaxation processes in undoped and modulation-doped InAs/GaAs self-assembled quantum dots (QDs) by using time-resolved spectroscopy technique with a time resolution of similar to 200 fs. We find that carrier capture and relaxation in the ground state of the charged QD are faster compared to the undoped dots even at an excitation level as low as 1x10(10) cm(-2). It is attributed to the triggering of the vibrating polarization field induced by the presence of cold carriers in the doped dots. The rate of an electron been captured by a positively charged QD is also calculated based on our proposed model. (c) 2006 American Institute of Physics.