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Analysis and design of wideband active power splitter with interleaf transmission line topology
(2019-11-01)
Huang, Ching-Ying
;
Hu, Robert
;
Niu, Dow-Chi
;
Chang, Chi-Yang
;
電機學院
This article proposes a new wideband active power splitter design where the gain cells along the input transmission line are arranged in interleaf rather than the conventional parallel style, thus the circuit's high-frequency performance can be greatly improved. Both theoretical analysis and circuit simulation have been carried out; as a demonstration, parallel and interleaf active power splitters are designed using 0.1 mu m GaAs pseudo-morphic heterostructure field effect transistors (GaAs pHEMT) process and measured on-wafer. The results clearly indicate the superiority of the interleaf topology. A 40 GHz interleaf active power splitter in 90 nm complementary metal-oxide-semiconductor (CMOS) is then presented where the magnitude and phase imbalance between the two output ports are 0.15 dB and 2.6 degrees at 20 GHz, and 0.16 dB and 14 degrees at 40 GHz. The output-port isolation is better than 30 dB across the whole frequency range.
Single-exciton energy shell structure in InAs/GaAs quantum dots
(2008-12-01)
Awirothananon, S.
;
Raymond, S.
;
Studenikin, S.
;
Vachon, M.
;
Render, W.
The energy shell structure of a single exciton confined in a self-assembled quantum dot (QD), including excited states, is studied in a regime where the direct Coulomb attraction energy is comparable to the kinetic energy of the carriers. This is achieved via magnetophotoluminescence excitation spectroscopy experiments, where a magnetic field applied perpendicular to the plane of the QD is used to reveal the angular-momentum content of energy shells. The absorption spectrum of the QDs is modeled, and comparison with experiment allows us to relate the observed transitions to interband QD bound-state transitions. The blueshift of the absorption peaks compared to the emission peaks is then interpreted in terms of many-body interactions, and we show that for a highly symmetric situation, the observed energy difference gives a direct measurement of the extra exchange energy gained upon addition of an extra exciton in the QD.
Impacts of structural asymmetry on the magnetic response of excitons and biexcitons in single self-assembled In(Ga)As quantum rings
(2009-08-01)
Lin, Ta-Chun
;
Lin, Chia-Hsien
;
Ling, Hong-Shi
;
Fu, Ying-Jhe
;
Chang, Wen-Hao
The diamagnetic shifts of neutral excitons and biexcitons confined in single self-assembled In(Ga)As/GaAs quantum rings are investigated. Unlike quantum dots, quantum rings reveal a considerably large biexciton diamagnetic shift, about two times larger than that of single excitons. Based on model calculations, we found that the inherent structural asymmetry and imperfection, combined with the interparticle Coulomb interactions, is the fundamental cause of the more extended biexciton wave function in the quantum rings. The exciton wave function tends to be localized in one of the potential valleys induced by structural imperfections of the quantum ring due to the strong localization of hole and the electron-hole Coulomb attraction, resembling the behavior in single dots. Our results suggest that the phase coherence of neutral excitons in quantum rings will be smeared out by such wave function localizations.
Photogeneration of coherent shear phonons in orientated wurtzite semiconductors by piezoelectric coupling
(2009-11-01)
Wen, Yu-Chieh
;
Ko, Tsung-Shine
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
;
Chyi, Jen-Inn
Using piezoelectric wurtzite semiconductor with accurate control of the crystal cut, we investigate the photogeneration of coherent shear acoustic phonons through anisotropic piezoelectric coupling. Theoretical study suggests the dominant contribution of the piezoelectric effect to the shear phonon generation in a-plane wurtzite GaN, which is also confirmed by the picosecond ultrasonic experiments with different dopant and excitation conditions. Piezoelectric transduction thus explains the observed remarkable coherent shear phonon signal. The influence of the ultrafast screening of surface electric field by photocarriers on the intensity and waveform of the generated shear acoustic pulse are discussed.
Recombination lifetimes in InN films studied by time-resolved excitation-correlation spectroscopy
(2009-11-01)
Liu, Horng-Chang
;
Hsu, Chia-He
;
Chou, Wu-Ching
;
Chen, Wei-Kuo
;
Chang, Wen-Hao
Recombination dynamics in degenerate InN were investigated by means of time-resolved excitation-correlation spectroscopy. The photoluminescence decay times are determined beyond the spectral response and temporal resolution limits of conventional photon-counting detectors. Spectral and temperature dependence of decay times reveal the effects of hole localizations on the recombination mechanisms. At low temperatures, the radiative lifetime tau(r) is insensitive to temperature and significantly longer than that predicted for the radiative band-to-band recombination, indicative of a transition dominated by the free-to-bound recombination without k conservation. Above a certain temperature determined by the electron concentration, we find tau(r)similar to T(3/2), as expected for the band-to-band transition when the k-selection rule holds. We determine a lower limit for the bimolecular recombination coefficient B in InN at 300 K as 5.6x10(-11) cm(3)/s.
Enhancing the Emission Efficiency of In0.2Ga0.8N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates
(2009-01-01)
Li, Zhen-Yu
;
Uen, Wu-Yih
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
In this paper, we report the fabrication of an In0.2Ga0.8N/GaN multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0-1 degrees by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the In0.2Ga0.8N/GaN MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the In0.2Ga0.8N/GaN MQW structure fabricated on 0.2 degrees off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be 7.4x10(-5). It is therefore manifested that an In0.2Ga0.8N/GaN MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of 14.2 ns and a lowest fluctuation of 5.6 meV in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2 degrees off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality In0.2Ga0.8N/GaN MQW blue light, emitting diode (LED) has been fabricated on 0.2 degrees off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of 465 nm and with the full width at half maximum of only 19 nm. The same device also showed an output power of 13.4 mW and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of In0.2Ga0.8N/GaN MQW blue LED fabricated thereon.
Simulation of 1300-nm In0.4Ga0.6As0.986N0.014/GaAs1-xNx quantum-well lasers with various GaAs1-xNx strain compensated barriers
(2004-11-01)
Chang, YA
;
Kuo, HC
;
Chang, YH
;
Wang, SC
;
光電工程學系
In this article, the laser performance of the 1300-nm In0.4Ga0.6As0.986N0.014/GaAs1 - xNx quantum-well (QW) lasers with various GaAs1 - xNx strain compensated barriers (x = 0%, 0.5%, 1%, and 2%) has been numerically investigated with a laser technology integrated simulation program. The simulation results suggest that with x = 0% and 0.5% can have better optical gain properties and high characteristic temperature coefficient To values of 110 and 94 K at the temperature range of 300-370 K. As the nitrogen composition in GaAs1 - xNx barrier increases more than 1% the laser performance degrades rapidly and the To value decreases to 87 K at temperature range of 300-340 K. This can be attributed to the decrease of conduction band carrier confinement potential between In0.4Ga0.6As0.986N0.014 QW and GaAs1 - xNx barrier and the increase of electronic leakage current. Finally, the temperature dependent electronic leakage current in the InGaAsN/GaAs1 - xNx quantum-well lasers are also investigated. (C) 2004 Elsevier B.V. All rights reserved.
Characteristics of emission polarization in a-plane nanorods embedded with InGaN/GaN multiple quantum wells
(2010-09-15)
Li, J. C.
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Lu, T. C.
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Huang, H. M.
;
Chan, W. W.
;
Kuo, H. C.
Nonpolar (a-plane) GaN nanorod arrays with embedded In(x)Ga(1-x)N/GaN (x=0.09, 0.14, 0.24, and 0.30) multiple quantum wells (MQWs) grown on r-plane sapphire have been fabricated successfully by self-assembled Ni nanomasks and subsequent inductively coupled plasma reactive-ion etching. After nanorod fabrications, the polarization ratio of the emission from MQWs with lower indium composition (x=0.09 and 0.14) slightly decreases but apparently increases by at most 79% for the samples with higher indium composition (x=0.24 and 0.30). Competition between the effect of multiple scattering, strain relaxation and reduction in localized centers, expected in a-plane MQW samples, are attributed to the variations in the polarization ratios after the nanorod formation. (c) 2010 American Institute of Physics. [doi:10.1063/1.3483239]
High extraction efficiency GaN-based light-emitting diodes on embedded SiO2 nanorod array and nanoscale patterned sapphire substrate
(2010-06-28)
Huang, Hung-Wen
;
Huang, Jhi-Kai
;
Kuo, Shou-Yi
;
Lee, Kang-Yuan
;
Kuo, Hao-Chung
In this paper, GaN-based LEDs with a nanoscale patterned sapphire substrate (NPSS) and a SiO2 photonic quasicrystal (PQC) structure on an n-GaN layer using nanoimprint lithography are fabricated and investigated. The light output power of LED with a NPSS and a SiO2 PQC structure on an n-GaN layer was 48% greater than that of conventional LED. Strong enhancement in output power is attributed to better epitaxial quality and higher reflectance resulted from NPSS and PQC structures. Transmission electron microscopy images reveal that threading dislocations are blocked or bended in the vicinities of NPSS layer. These results provide promising potential to increase output power for commercial light emitting devices. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456385]
The influences of surface treatment and gas annealing conditions on the inversion behaviors of the atomic-layer-deposition Al2O3/n-In0.53Ga0.47As metal-oxide-semiconductor capacitor
(2010-07-26)
Trinh, H. D.
;
Chang, E. Y.
;
Wu, P. W.
;
Wong, Y. Y.
;
Chang, C. T.
The inversion behaviors of atomic-layer-deposition Al2O3/n-In0.53Ga0.47As metal-oxide-semiconductor capacitors are studied by various surface treatments and postdeposition annealing using different gases. By using the combination of wet sulfide and dry trimethyl aluminum surface treatment along with pure hydrogen annealing, a strong inversion capacitance-voltage (C-V) response is observed, indicating a remarkable reduction in interface trap state density (D-it) at lower half-part of In0.53Ga0.47As band gap. This low D-it was confirmed by the temperature independent C-V stretch-out and horizontal C-V curves. The x-ray photoelectron spectroscopy spectra further confirm the effectiveness of hydrogen annealing on the reduction of native oxides. (C) 2010 American Institute of Physics. [doi:10.1063/1.3467813]

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