Browsing by Author "Lee, CP"

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980 nm InGaAs/AlGaAs quantum well lasers with extremely low beam divergence
(1996)
Yen, ST
;
Lin, G
;
Liu, DC
;
Tsai, CM
;
Lee, CP
A computational efficient method for HBT intermodulation distortions and two-tone characteristics simulation
(2001)
Huang, KY
;
Li, YM
;
Lee, CP
;
Sze, SM
;
電子工程學系及電子研究所
In this paper, a new simulation method for two-tone characteristics calculations and the third-order intercept point (OIP3) of heterojunction bipolar transistor (HBT) in large-scale time domain is proposed. Base on waveform relaxation (WR) and monotone iterative (MI) methods, we solve a set of nonlinear ordinary differential equation (ODE) of equivalent circuit. With this approach, the two-tone characteristics in frequency domain for HBTs were directly computed from time domain result with fast Fourier transform (FFT). Simulation results on a realistic HBT are presented to show the accuracy and efficiency of the method.
A computational method for energy level spin splitting simulation in InAs/GaAs semiconductor quantum dots
(2002-05-01)
Li, YM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
;
Tretyak, O
An impact of the spin-orbit interaction on the electron quantum confinement is considered theoretically for narrow gap semiconductor cylindrical quantum dots. To study the phenomena for InAs quantum dot embedded into GaAs semiconductor matrix, the effective one electronic band Hamiltonian, the energy position dependent electron effective mass approximation, and the spin-dependent Ben Daniel-Duke boundary conditions axe considered, formulated and solved numerically. To solve the nonlinear Schrodinger equation, we propose a nonlinear iterative algorithm. This calculation algorithm not only converges for all simulation cases but also has a good convergent rate. With the developed quantum dot simulator, we study the effect of the spin-orbit interaction for narrow gap InAs/GaAs semiconductor cylindrical quantum dots. From the numerical calculations, it has been observed that the spin-orbit interaction leads to a sizeable spin-splitting of the electron energy states with nonzero angular momentum. Numerical evidence is presented to show the splitting result is strongly dependent on the quantum dot size.
A CPW-to-Slotline active gunn diode leaky wave antenna
(1998)
Lee, SH
;
Wu, JJ
;
Peng, ST
;
Hu, CC
;
Jou, CF
A X-band coplanar waveguide (CPW) to slotline couple feeding active microstrip leaky wave antenna using Gunn-diode oscillator as source is demonstrated. The method to excite the first higher order mode of the microstrip leaky wave antenna is to put the CPW-to-slotline transition underneath the middle of the microstrip line, and the oscillator circuit and radiating element are separated by a ground plane. The measured angle of the maximum beam direction of active antenna is at 72 degrees for the active Gunn oscillator frequency of 11.218 GHz; This prototype of active leaky wave antenna feeding by Gunn diode oscillator with CPW-to-slotline structure can be easily scaled up to millimeter wave frequency region.
A detailed study of non-uniform quantum well infrared photodetectors
(2001-06-01)
Wang, SY
;
Chin, YC
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A non-uniform quantum well infrared photodetector (NUQWIP) structure is studied. By changing the doping concentration and barrier width of each quantum well, the electric field distribution can be tailored. Different transition types of NUQWIPs were fabricated. Suppressed dark current is obtained for all the NUQWIPs. The NUQWIPs show excellent performance compared with conventional uniform structures. The dark current is about an order of magnitude lower and the background limited temperature increases for 6 degrees. The electric field distribution within the structure is calculated to explain the results and characteristics of the NUQWIPs. The NUQWIP is found to be advantageous for the low cutoff energy detectors using B-C transitions. (C) 2001 Published by Elsevier Science B.V.
A Gunn-diode active leaky-wave frequency scanning antenna
(1998-01-01)
Lee, SH
;
Jou, CK
;
Lee, CP
;
Hu, CC
;
Wu, JJ
A frequency tunable active leaky-wave scanning antenna using Gunn-diode voltage control oscillator (VCO) as source is developed. The frequency tuning controlled by changing either the varactor diode de bias or the Gunn diode de bias is demonstrated. The measured scanning angle of active antenna is close to 15 degree as the Gunn VCO frequency tuned from 12.58GHz to 12.98GHz. To excite the first higher order mode of the microstrip leaky-wave antenna is fed asymmetrically. The dominant mode excitation has been successfully suppressed by adding a sequence of covered wire in the middle line of the microstrip leaky wave antenna. This is a prototype of frequency scanning antenna using two terminal device, which can be easily scaled up to millimeter wave frequency region.
A light-induced tunneling state in a submicron double barrier tunneling diode with a center-doped well
(2000-02-01)
Suen, YW
;
Young, CC
;
Chang, CJ
;
Wu, JC
;
Wang, SY
We will present the observation of a light-induced meta-stable impurity state in a submicron center-doped double barrier tunneling diode (DBRTD) manufactured by a novel single-step e-beam lithography process in which no further alignment for the interconnect between the bonding pad and the small active device region is required. We attribute the mete-stable tunneling state, which can be switched by light and high voltage bias, to the light- or field-induced charge redistribution in the active tunneling region. (C) 2000 Elsevier Science B.V. All rights reserved.
A novel cladding structure for semiconductor quantum-well lasers with small beam divergence and low threshold current
(1996-09-01)
Yen, ST
;
Lee, CP
;
交大名義發表
;
電子工程學系及電子研究所
;
National Chiao Tung University
A novel cladding structure is proposed and analyzed for semiconductor quantum-well lasers ttl achieve a small vertical-beam divergence and a low threshold current density simultaneously, This cladding structure is designed to guide a wide optical mode but with a high peak intensity in quantum wells. The wide expansion of the optical mode results in a small beam divergence. In addition, the high optical intensity in quantum wells causes a low threshold current density, This novel cladding structure is optimized. The result shows that this type of cladding structures can achieve a beam divergence as small as 14.6 degrees while the threshold current density remains small.
A novel cladding structure for semiconductor quantum-well lasers with small beam divergence and low threshold current
(1996-09-01)
Yen, ST
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A novel cladding structure is proposed and analyzed for semiconductor quantum-well lasers ttl achieve a small vertical-beam divergence and a low threshold current density simultaneously, This cladding structure is designed to guide a wide optical mode but with a high peak intensity in quantum wells. The wide expansion of the optical mode results in a small beam divergence. In addition, the high optical intensity in quantum wells causes a low threshold current density, This novel cladding structure is optimized. The result shows that this type of cladding structures can achieve a beam divergence as small as 14.6 degrees while the threshold current density remains small.
A novel energy filter using semiconductor superlattices and its application to tunneling time calculations
(1996-12-01)
Tung, HH
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
An artificial quantum-mechanical filter using superlattice structures is proposed in this paper, By gradually changing the barrier widths of a superlattice according to a Gaussian function, a broad-band and almost zero sidelobe transmission profile can be obtained. The WKB approximation is applied to demonstrate the phenomena of abrupt change of transmission profile, The proposed structure allows the incident electrons to be nearly totally transmitted when the impinging electron energy is in the passband, On the other hand, a complete reflection occurs when the impinging energy is in the stopband, By adjusting the structure parameters, the desired passband and stopband of such a filter can be obtained, Time evolution of an electron wavepacket moving through the structure is calculated by numerically solving the time-dependent Schrodinger equation, Numerical results clearly demonstrate the characteristics of total transmission and reflection, By simulating the movement of a totally transmitted wavepacket, ambiguity results from the nature of the wavepacket in the determination of electron tunneling time can be avoided. The generalized concept of matched quantum-mechanical wave impedance (QMWI) analogous to transmission line theory is presented to explaine the occurrence of total transmission of the proposed structure, The tunneling time (tau(QMWI)) calculated based on the concept of QMWI is compared with the accurate tunneling time obtained by our simulation.
A novel energy filter using semiconductor superlattices and its application to tunneling time calculations
(1996-12-01)
Tung, HH
;
Lee, CP
;
交大名義發表
;
電子工程學系及電子研究所
;
National Chiao Tung University
An artificial quantum-mechanical filter using superlattice structures is proposed in this paper, By gradually changing the barrier widths of a superlattice according to a Gaussian function, a broad-band and almost zero sidelobe transmission profile can be obtained. The WKB approximation is applied to demonstrate the phenomena of abrupt change of transmission profile, The proposed structure allows the incident electrons to be nearly totally transmitted when the impinging electron energy is in the passband, On the other hand, a complete reflection occurs when the impinging energy is in the stopband, By adjusting the structure parameters, the desired passband and stopband of such a filter can be obtained, Time evolution of an electron wavepacket moving through the structure is calculated by numerically solving the time-dependent Schrodinger equation, Numerical results clearly demonstrate the characteristics of total transmission and reflection, By simulating the movement of a totally transmitted wavepacket, ambiguity results from the nature of the wavepacket in the determination of electron tunneling time can be avoided. The generalized concept of matched quantum-mechanical wave impedance (QMWI) analogous to transmission line theory is presented to explaine the occurrence of total transmission of the proposed structure, The tunneling time (tau(QMWI)) calculated based on the concept of QMWI is compared with the accurate tunneling time obtained by our simulation.
A time-domain approach to simulation and characterization of RF HBT two-tone intermodulation distortion
(2003-10-01)
Huang, KY
;
Li, YM
;
Lee, CP
;
電子工程學系及電子研究所
;
友訊交大聯合研發中心
In this paper, we evaluate the two-tone intermodulation distortion for heterojunction bipolar transistors (HBTs) operated at RF. We directly solve the nonlinear differential equations of the HBT large-signal model in time domain by employing the waveform-relaxation and monotone-iterative methods. Based on time-domain results, sinusoidal waveform outputs are transformed into the frequency domain with the fast Fourier transform. Furthermore, the output third-order intercept-point values of the HBT are computed with the spectra. Results for a fabricated InGaP HBT under different testing conditions are reported and compared among the HSPICE results, the results with harmonic balance methodology, and the measured data. Comparisons among these results show that our method demonstrates its superiority over the conventional approaches. This characterization alternative has allowed us to study RF device properties, perform thermal consumption and sensitivity analysis, and extract model parameters.
A voltage-tunable multicolor triple-coupled InGAs/GaAs/AlGaAs quantum-well infrared photodetector for 8-12 mu m detection
(1996-10-14)
Chiang, JC
;
Li, SS
;
Tidrow, MZ
;
Ho, P
;
Tsai, M
A voltage-tunable multicolor triple-coupled quantum-well infrared photodetector (TC-QWIP) has been developed for 8-12 mu m detection. The TC-QWIP consists of three coupled quantum wells formed by an enlarged Si-doped InxGa1-xAs quantum well and two undoped GaAs quantum wells separated by two thin AlyGa1-yAs barriers. Two TC-QWIP structures with varying indium and aluminum compositions were designed and demonstrated. Due to the strong coupling effect of the asymmetrical quantum wells, three bound states (E(1), E(2), E(3)) are formed inside the quantum wells of the TC-QWIP. The main detection peak wavelength is due to E(1)-->E(3) bound states transition for both devices, while two secondary detection peaks due to E(1)-->E(2) and E(1)-->E(c) continuum states transitions under different biases were also observed. In addition, a strong quantum-confined Stark shift effect for the E(1)-->E(3) transition was observed in the wavelength range of 8.2-9.1 and 10.8-11.5 mu m for QWIP-A and QWIP-B, respectively; both devices exhibit a linear dependence of detection peak wavelength on the applied bias voltage. A spectral responsivity of R(i)=0,05 A/W and background limited performance (BLIP) detectivity D-BLIP*=6.1x10(9) cm root HZ/W were obtained at V-b=5 V, lambda(p)=8.6 mu m, and T-BLIP=66 K for QWIP-A, while R(i)=0.33 A/W and D-BLIP*=1.63x10(10) cm root Hz/W at V-b=4 V, pi(p)=11.2. mu m, and T-BLIP-50 K were obtained for QWIP-B. (C) 1996 American Institute of Physics.
A voltage-tunable multicolor triple-coupled InGAs/GaAs/AlGaAs quantum-well infrared photodetector for 8-12 mu m detection
(1996-10-14)
Chiang, JC
;
Li, SS
;
Tidrow, MZ
;
Ho, P
;
Tsai, M
A voltage-tunable multicolor triple-coupled quantum-well infrared photodetector (TC-QWIP) has been developed for 8-12 mu m detection. The TC-QWIP consists of three coupled quantum wells formed by an enlarged Si-doped InxGa1-xAs quantum well and two undoped GaAs quantum wells separated by two thin AlyGa1-yAs barriers. Two TC-QWIP structures with varying indium and aluminum compositions were designed and demonstrated. Due to the strong coupling effect of the asymmetrical quantum wells, three bound states (E(1), E(2), E(3)) are formed inside the quantum wells of the TC-QWIP. The main detection peak wavelength is due to E(1)-->E(3) bound states transition for both devices, while two secondary detection peaks due to E(1)-->E(2) and E(1)-->E(c) continuum states transitions under different biases were also observed. In addition, a strong quantum-confined Stark shift effect for the E(1)-->E(3) transition was observed in the wavelength range of 8.2-9.1 and 10.8-11.5 mu m for QWIP-A and QWIP-B, respectively; both devices exhibit a linear dependence of detection peak wavelength on the applied bias voltage. A spectral responsivity of R(i)=0,05 A/W and background limited performance (BLIP) detectivity D-BLIP*=6.1x10(9) cm root HZ/W were obtained at V-b=5 V, lambda(p)=8.6 mu m, and T-BLIP=66 K for QWIP-A, while R(i)=0.33 A/W and D-BLIP*=1.63x10(10) cm root Hz/W at V-b=4 V, pi(p)=11.2. mu m, and T-BLIP-50 K were obtained for QWIP-B. (C) 1996 American Institute of Physics.
An energy band-pass filter using superlattice structures
(1996-03-01)
Tung, HH
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A novel quantum mechanical energy band-pass filter (EBPF) using semiconductor superlattices is proposed. Such structures with a Gaussian superlattice potential profile allow the incident electrons to be nearly totally transmitted when the impinging electron energy is in the passband. On the other hand, a complete reflection occurs when the impinging energy is in the stopband, By adjusting the parameters of the potential profile and the superlattice, the desired passband and stopband of such filter can be obtained, Time evolution of an electron wave packet moving through such a structure is calculated by numerically solving the time-dependent Schrodinger equation. The numerical simulation clearly demonstrates the characteristics of total transmission and total reflection, The generalized concept of matched quantum-mechanical wave impedance (QMWI) analogous to that used in the transmission line theory is presented to explain the occurrence of total transmission of the proposed structures.
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.
Calculation of induced electron states in three-dimensional semiconductor artificial molecules
(2002-08-01)
Li, YM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
;
友訊交大聯合研發中心
The energy levels calculation of electrons confined in small three-dimensional (3D) coupled quantum InxGa1-xAs dots embedded in GaAs semiconductor matrix is presented. The quantum dots have disk shapes and are separated (in the disk symmetry axis direction) by a certain distance. Based on the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, a finite height hard-wall 3D confinement potential, and the Ben Daniel-Duke boundary conditions, the problem is formulated and solved for the disk-shaped coupled quantum dots. To calculate the ground and induced state energy levels, the nonlinear 3D Schrodinger equation (SE) is solved with a developed nonlinear iterative method to obtain the final self-consistent solutions. In the iteration loops, the Schrodinger equation is discretized with a nonuniform mesh finite difference method, and the matrix eigenvalue problem is solved with the balanced and shifted QR method. Our complete 3D approach demonstrates a principal possibility that the number of bound electronic states in the system can be changed when the interdot (vertical) distance is modified. However, it is impossible to produce an additional possibility to manipulate the system electronic properties within only a two-dimensional (2D) simulation. (C) 2002 Elsevier Science B.V. All rights reserved.
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.
Carrier-carrier scattering in GaAs/AlxGa1-xAs quantum wells
(2000-06-15)
Sun, KW
;
Song, TS
;
Sun, CK
;
Wang, JC
;
Kane, MG
We have studied carrier dynamics in highly nonequilibrium two-dimensional (2D) carrier distributions generated with femtosecond laser pulses in p-doped GaAs/Al0.32Ga0.68As quantum wells at photoexcited carrier densities between 10(9) and 10(11) cm(-2). The initially nonthermal carrier distribution is quickly broadened due to inelastic carrier-carrier scattering, with the broadening rate increasing as carrier density is increased. Measurements of the unrelaxed peak height in the hot electron-neutral acceptor luminescence spectra are compared with calculations of the carrier distribution using integration of the 2D dynamically screened Boltzmann equation. Our results indicate that carrier-carrier scattering becomes as significant a scattering mechanism as LO-phonon emission at density of about 10(10) cm(-2).
Carrier-carrier scattering: an experimental comparison of 5 and 3 nm AlxGa1-xAs/GaAs quantum wells
(2000)
Sun, KW
;
Sun, CK
;
Wang, JC
;
Wang, SY
;
Lee, CP
We have studied carrier dynamics among highly nonequilibrium carrier distributions generated with femtosecond laser pulses in Be:AlxGa1-xAs/GaAs quantum wells with different well width at hot carrier densities between 10(9) and 10(11) cm(-2). The spectra, at moderately high densities (greater than or equal to 10(10) cm(-2)) indicate that the initially narrow electron distribution is altered in a time less than or equal to the LO-phonon emission time, as a result of rapid carrier-carrier scattering. At an excitation density of about 10(10) cm(-2), the carrier-carrier scattering rate is faster in narrower quantum wells. By measuring the intensity of the unrelaxed peak, it is possible to determine the relative rates of carrier-carrier scattering and LO-phonon emission. Our results indicate that carrier-carrier scattering becomes as significant as LO-phonon emission at a density of about 1 x 10(10) cm(-2) in the 5 nm quantum wells. (C) 2000 Elsevier Science Ltd. All rights reserved.