Browsing by Author "Lin, SD"

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An investigation of quantum states in ultra-small InAs/GaAs quantum dots by means of photoluminescence
(2005-08-01)
Wu, CH
;
Lin, YG
;
Tyan, SL
;
Lin, SD
;
Lee, CP
The quantum states of InAs/GaAs quantum dots (QDs) with a base length of less than 10 nm are studied by means of excitation and temperature dependent photoluminescence (PL). The base length of the QDs, calculated by the PL ground state transition energy, is in agreement with the atomic force microscopy measurements. By means of the excitation-dependent PL, we demonstrate that only the ground electron and hole states exist when the base length of the QDs is smaller than about 7.3 nm, whereas larger dots, with a base length of about 8.7 nm, give rise to one excited hole state. The measured energy separation between the ground and the excited hole states is in good agreement with the theoretical calculation. The transition energy in the temperature-dependent PL spectra shows a rapid redshift as the temperature is raised higher than the critical temperature. The redshift rate is about 2.8 and 2.5 times larger than the values calculated by Varshni's law for small and large dots, respectively. The higher redshift rate can be explained by the stronger tunneling effect. In addition, the PL linewidths show a V-shaped dependence on the temperature. This behavior can be described as a tunneling and electron-phonon scattering effect.
Composition determination of semiconductor quantum wires by X-ray scattering
(2005-02-28)
Hsu, CH
;
Tang, MT
;
Lee, HY
;
Huang, CM
;
Liang, KS
Self-assembled semiconductor nano-structures, e.g. quantum dots and wires, have recently attracted intensive interests due to their potential applications in optoelectronic industry. Strain field, compositional profile, size, and shape are the key factors determining the physical properties of these nano-structures. However, due to their mesoscopic size, it is a challenge to accurately determine those geometric and chemical parameters. In this work, we present the structural and compositional investigation of GaAs quantum wires grown on InP(0 0 1) substrates by grazing incidence X-ray scattering. In particular, we applied resonant X-ray scattering to determine the compositional distribution within the wires. With properly chosen diffraction peak and X-ray energy range, the profile of energy scan is highly sensitive to the composition of the region with selected lattice constant. As compared to other composition determination methods, which rely on the intensity ratio either between a strong and a weak diffraction or between the same Bragg diffraction collected at different energies, the profile of energy scan is not affected by the significant intensity modulation introduced by inter-wire correlation. Therefore, this method can be applied to systems of various surface morphologies and ordered structures and still provides compositional information with high accuracy and good resolution. (C) 2004 Elsevier B.V. All rights reserved.
Deep level transient spectroscopy characterization of InAs self-assembled quantum dots
(2001-01-15)
Ilchenko, VV
;
Lin, SD
;
Lee, CP
;
Tretyak, OV
;
電子工程學系及電子研究所
Deep level transient spectroscopy (DLTS) was used to obtain the energy level and the capture characteristics of InAs self-assembled quantum dots embedded in GaAs. A specially designed structure was used for the DLTS measurement for enhanced resolution. This structure allows us to detect capacitance relaxation signal from a single layer of quantum dots and to separate this signal from those of the DX centers inside the structure. The DLTS spectra with different filling pulses and different rate windows provide clear information on the energy level and the capture characteristics of the quantum dots. (C) 2001 American Institute of Physics.
DLTS characterization of InAs self-assembled quantum dots
(2000)
Ilchenko, VV
;
Lin, SD
;
Lee, CP
;
Tretyak, OV
;
交大名義發表
Deep level capacitance transient spectroscopy was used to obtain the energy level and the capture characteristics of InAs self-assembled quantum dots embedded in GaAs. A specially designed structure was used for the DLTS measurement for enhanced resolution. This structure allows us to detect capacitance relaxation signal from a single layer of quantum dots and to separate this signal from those of the DX centers inside the structure. The DLTS spectra with different filling pulses and different rate windows provide clear information on the energy level and the capture characteristics of the quantum dots.
GaAs metal-semiconductor-metal photodetectors with low dark current and high responsivity at 850 nm
(2002-12-01)
Lin, SD
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this paper, we report on the fabrication a GaAs metal-semiconductor-metal photodetector with both low dark current and high responsivity at 850 nm. By using the Schottky contacts modified by a thin, n(+)-doped layer on the surface of the devices, the lowest dark current density of about 4.5 x 10(-7) cm(-2) was achieved. Besides, in the same devices, the responsivity resulting from a newly designed resonant-cavity-enhanced structure with a superlattice distributed Bragg reflector was about 0.34 A W-1 at 850 nm. The equivalent external quantum efficiency of the devices with equal finger spacing and finger width was about 48%. Our design is relatively easy and reproducible for both the sample growth and the device process.
High performance InAs/GaAs quantum dot infrared photodetectors with AlGaAs current blocking layer
(2001-06-01)
Wang, SY
;
Lin, SD
;
Wu, HW
;
Lee, CP
;
電子工程學系及電子研究所
Low dark current InAs/GaAs quantum dot infrared photodetector (QDIP) is demonstrated. The dark current reduced for over three orders of magnitude by introducing a thin AlGaAs current blocking layer. This thin AlGaAs can reduce the dark current much more than the response signal. The responsivity at 0.5 V is 0.08 A/W with peak at 6.5 mum and the corresponding detectivity about 2.5 x 10(9) cm Hz(1/2/W1/2). It is the highest detectivity reported for QDIP at 77 K. (C) 2001 Published by Elsevier Science B.V.
Hole Schottky barrier height enhancement and its application to metal-semiconductor-metal photodetectors
(2001-12-01)
Lin, SD
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Hole Schottky barrier heights on GaAs have been studied experimentally by using a conventional metal-semiconductor-metal photodetector (MSMPD) structure. The Schottky barrier height for holes was obtained directly by the hole-current dominated dark current measurement of the MSMPD. With a thin, highly doped surface layer, control of the Schottky barrier heights for holes from 0.48 to 0.79 eV was obtained. By using these engineered Schottky contacts in the MSMPDs, over three orders of magnitude reduction in the dark currents of the MSMPDs was achieved. (C) 2001 American Institute of Physics.
InAs/GaAs quantum dot infrared photodetectors with different growth temperatures
(2003-10-01)
Wang, SY
;
Chen, SC
;
Lin, SD
;
Lin, CJ
;
Lee, CP
InAs/GaAs quantum dot infrared photodetectors were fabricated with quantum dots grown at three different temperatures. Large detection wavelength shift (5-14.5 mum) was demonstrated by changing 40 degrees of the epitaxy temperature. The smaller quantum dots grown at lower temperature generate 14.5 mum responses. The detectivity of the normal incident 15 mum QDIP at 77 K is 3 x 10(8) cm Hz(1/2)/W. A three-color detector was also demonstrated with quantum dots grown at medium temperature. The three-color detection comes from two groups of different sizes of dots within one QD layer. This new type of multicolor detector shows unique temperature tuning behavior that was never reported before. (C) 2003 Elsevier B.V. All rights reserved.
Investigation of electron-optical phonon interactions in moderate wide InxGa1-xAs/GaAs strained quantum wells
(2001-12-01)
Lin, SD
;
Lee, HC
;
Sun, KW
;
Lee, CP
;
電子工程學系及電子研究所
In this presentation, we have calculated the electron-optical phonon scattering rate of GaAs/AlAs quantum wells and average electron energy loss rate as a function of well width of the GaAs/AlxGa1-xAs quantum wells. We have also studied the Raman and hot electron-neutral acceptor luminescence in moderate wide InxGa1-xAs/GaAs strained quantum wells (with 10 nm in well width and 30 nm in barrier width) to determine the dominant phonon mode emitted by the hot electrons in the wells at 15 K. The hot electron-neutral acceptor luminescence spectrum of the strained quantum well sample shows an oscillation period of about 22 meV which indicates that the hot electrons relaxed mostly through emissions of the InAs confined phonons. (C) 2001 Elsevier Science B.V. All rights reserved.
Low dark current quantum-dot infrared photodetectors with an AlGaAs current blocking layer
(2001-02-19)
Wang, SY
;
Lin, SD
;
Wu, HW
;
Lee, CP
;
電子工程學系及電子研究所
Low dark current InAs/GaAs quantum-dot infrared photodetectors (QDIPs) are demonstrated. The dark current is reduced by over three orders of magnitude by using a thin AlGaAs current blocking layer. This thin AlGaAs layer reduces the dark current much more than the response signal. The responsivity at 0.5 V is 0.08 A/W with a peak detection wavelength at 6.5 mum. The corresponding detectivity is 2.5x10(9) cm Hz(1/2)/W-1/2, which is the highest detectivity reported for a QDIP at 77 K. (C) 2001 American Institute of Physics.
Multicolor infrared detection realized with two distinct superlattices separated by a blocking barrier
(2002-04-01)
Chen, CC
;
Chen, HC
;
Kuan, CH
;
Lin, SD
;
Lee, CP
A multicolor infrared photodetector was realized with two superlattices separated by a blocking barrier. The photoresponse is switchable between 7.5-12 and 6-8.5 mum by the bias polarity, and is also tunable by the bias magnitude in each wavelength regime. In addition, our detector exhibits advantages including little temperature dependence of the spectral response and the same order of responsivity in the two wavelength regimes. The measured peak responsivities in the two regimes are 117 mA/W at 9.8 mum under 1 V and 129 mA/V at 7.4 mum under -0.8 V, respectively. Also, the detectivities are comparable with the conventional multistack detector. The zero background peak detectivities are 2.3x10(10) cm Hz(0.5)/W at 50 K and 9.8 mum under 0.7 V, and 8.7x10(10) cm Hz(0.5)/W at 70 K and 7.4 mum under -0.7 V. (C) 2002 American Institute of Physics.
Photoluminescence of ultra small InAs/GaAs quantum dots
(2005-08-10)
Lin, YG
;
Wu, CH
;
Tyan, SL
;
Lin, SD
;
Lee, CP
The InAs/GaAs quantum dots (QDs) with a baselength of less than 10 nm are studied by the excitation-, temperature-dependent and magneto-photoluminescence (PL). The baselengths of the QDs, calculated by the PL ground state transition energy and estimated by magneto-PL spectra, axe in agreement with the result of atomic force microscopy measurements. By means of the excitation-dependent PL, we demonstrate that only the ground electron and hole states exist when the baselength of the QDs is smaller than about 7.3 nm, whereas the larger dots with a baselength of about 8.7 nm will give rise to one excited hole state. The measured energy separation between the ground and the excited hole states is in good agreement with the theoretical calculation. The transition energy in temperature-dependent PL spectra shows a rapid redshift as the temperature is higher than the critical temperature. The redshift rate is about 2.8 and 2.5 times larger than the values calculated by Varshni's law for small and large dots respectively. The higher redshift rate can be explained by the stronger tunneling effect. In addition, the PL linewidths show a V-shape dependence with the temperature. This behavior could be well described as a tunneling and electron-phonon scattering effect.
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.
Self-assembled GaAs antidots growth in InAs matrix on (100) InAs substrate
(2005-01-01)
Lin, SD
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We have grown GaAs antidots in InAs matrix on (10 0) InAs substrate successfully. The quantum-sized 3-D islands were observed clearly in both AFM and TEM measurements. From these observations, the 2-D to 3-D transition thickness is determined to be between 2.25 and 2.5 ML. For 2.5 ML GaAs deposition, the grown antidots have a size of about 15-35 nm in base diameter and about 2-4 run in height with a density about 3-4 x 10(10) cm(-2). (C) 2003 Elsevier B.V. All rights reserved.
Self-assembled GaAs antiwires in In0.53Ga0.47As matrix on (100) InP substrates
(2002-10-14)
Lin, SD
;
Lee, CP
;
Hsieh, WH
;
Suen, YW
;
電子工程學系及電子研究所
The growth of GaAs antiwires in the In0.53Ga0.47As matrix on InP substrate has been investigated. The periodic, wire-like structure was obtained when a proper amount of GaAs was deposited. The grown antiwires have a height about 1.2-2.0 nm and a period about 23 nm. Using an In0.53Ga0.47As/In0.52Al0.48As modulation-doped structure, the effect of the GaAs antiwires on the two-dimensional electron gas mobility was investigated. For the sample with antiwires near the two-dimensional channel, a significant anisotropy in low temperature mobility was observed. (C) 2002 American Institute of Physics.
Thermal stability of plasma-treated ohmic contacts to n-GaN
(2003-04-01)
Lee, CC
;
Lin, SD
;
Lee, CP
;
Yeh, MH
;
Lee, WI
In this study, the thermal stability of plasma-treated ohmic contacts by either Cl-2/Ar or Ar plasma to n-GaN was investigated by high-temperature aging tests. With proper plasma treatment, ohmic contacts to n-GaN have a lower contact resistance than those without plasma treatment. High-temperature aging tests were performed at temperatures ranging from 400 to 600degreesC for 2h in N-2 or air ambient. No apparent electrical degradation in contact resistance was observed after aging, showing the thermal stability of plasma-treated ohmic contacts is not affected by the recovery of plasma-induced damages on the wafer surface.
Tunneling through InAs quantum dots in AlGaAs/GaAs double barrier resonant tunneling diodes with InGaAs quantum well emitters
(2003-03-01)
Lin, SD
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Using InGaAs quantum well emitters, AlGaAs/GaAs double barrier resonant tunneling diodes with and without self-assembled InAs/GaAs quantum dots (QDs) have been studied extensively. Because the energy state of the emitter was lower than the level of the ground state within InAs QDs, the resonant tunneling was observed clearly near zero bias in all devices. From the results of bias-dependent photoluminescence and current-voltage characteristics, we obtain unambiguously the resonant tunneling through the InAs QDs, both controllably and reproducibly. (C) 2003 American Institute of Physics.