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Abnormal PL spectrum in InGaN MQW surface emitting cavity
(2008-01-01)
Chu, J. T.
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Cheng, Y. -J.
;
Kuo, H. C.
;
Lu, T. C.
;
Wang, S. C.
We report the observation of an abnormal photoluminescent (PL) spectrum from a HeCd laser pumped InGaN multiple quantum well (MQW) vertical cavity. The device is fabricated using standard MOCVD deposition on a (0001)-oriented sapphire substrate. The layer structures are: 10nm nucleation layer, a 4um bulk GaN layer, InGaN MQWs, and a final 200nm GaN cap layer. The InGaN MQWs consist of 10 pairs of 5 nm GaN barrier and 3 run In0.1Ga0.9N well. The peak emission of the as-grown MQWs sample was similar to 420nm. A dielectric distributed Bragg reflectors (DBR) were then coated on the top layer, followed by a laser lift off from sapphire substrate, and subsequently another DBR coated on the bulk GaN bottom surface. The cavity has a quality factor of similar to 520 from 400-490nm. The device was pumped by a focused CW HeCd laser from the bulk GaN side. When the laser is focused onto the InGaN MQWs, a photoluminescent spectrum centered at the designed MOW wavelength was observed as expected. However, when the focused position was moved toward the bulk GaN region, an additional abnormal PL peak around 460nm was observed. This is far outside the designed MQW wavelength.
Effects of substrate temperature on properties of Alq3 amorphous layers prepared by vacuum deposition
(2006-01-01)
Chiu, K. C.
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Jian, Z. A.
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Luo, Y. Z.
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Chung, J. M.
;
Tang, S. J.
In this report, various organic Alq3 amorphous layers are prepared by vacuum deposition at different substrate temperatures T-sub (from 30 to 180 degrees C). The surface morphology, structural information, electrical and optical properties of these as-deposited layers are investigated by atomic force microscopy, X-ray diffraction, J-E curves, and photoluminescence studies, respectively. Furthermore, a temperature dependence of dark electrical conductivity sigma(T) deduced from J-E curves of these organic amorphous layers is presented. Finally, effects from T-sub on the physical properties of these organic Alq3 amorphous layers are discussed and a model based on a thermal interconversion between Alq3 isomers is proposed to explain these experimental results.
Single-exciton energy shell structure in InAs/GaAs quantum dots
(2008-12-01)
Awirothananon, S.
;
Raymond, S.
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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.
The Effect of Tensile Strain on Optical Anisotropy and Exciton of m-Plane ZnO
(2015-04-01)
Wang, H. H.
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Tian, J. S.
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Chen, C. Y.
;
Huang, H. H.
;
Yeh, Y. C.
The near band edge emission of the tensile-strained m-plane ZnO film grown on (112)LaAlO3 substrates shows abnormal low polarization degree (rho = 0.1). The temperature dependency of polarization degree clarifies the origins of different emission peaks. In tensile-strained m-plane ZnO, the [0001] polarized state is upper shifted and is overlapping with the [11 (2) over bar0] polarized state. This phenomenon causes the abnormal low polarization degree and reveals the effect of strain on the emission anisotropy of m-plane ZnO.
Recombination lifetimes in InN films studied by time-resolved excitation-correlation spectroscopy
(2009-11-01)
Liu, Horng-Chang
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Hsu, Chia-He
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Chou, Wu-Ching
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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.
單一量子點之磁光與糾纏態特性( II )
(2011)
林聖迪
;
LIN SHENG DI
;
國立交通大學電子工程學系及電子研究所
Photoluminescence studies of GaN films of different buffer layer and doping concentration
(1998-02-01)
Shen, CC
;
Shu, CK
;
Lin, HC
;
Ou, J
;
Chen, WK
Photoluminescence (PL) measurements of GaN films with various buffer thicknesses and Si-doping concentrations have been carried out. PL response of one specific sample was studied for temperature dependence. The results showed that the band gap energy reduction is linearly proportional to the temperature increase with a slope of similar to-4 x 10(-4) eV.K-1 and that the activation energies for donor-bound and acceptor-bound exciton transitions are 15 and 18 meV, respectively. In Si-doped GaN films, the PL data indicated that the reduced gap depends on the third power of carrier concentration as n(1/3). We also obtained a concentration coefficient of 2.34 x 10(-4) eV.cm and a band gap energy of 3.426 eV in the undoped GaN film.
Interrelation of transport and optical properties in gold nanoclusters
(2010-09-20)
Shu, G. W.
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Chen, T. Y.
;
Shen, J. L.
;
Lin, C. A. J.
;
Chang, W. H.
Temperature dependence of the electrical conductivity and photoluminescence (PL) in Au nanoclusters (NCs) is investigated. The correlation of the conductivity and PL in Au NCs at different temperatures is evident: (i) for T < 50 K, both the conductivity and PL intensity decrease with temperature, which suggests thermal structural fluctuations; (ii) for 50 K < T < 90 K, conductivity and PL are explained by variable range hopping; (iii) for 90 K < T < 170 K, simple thermal activated hopping dominates in conductivity, with a rate-equation model proposed to analyze the carrier transfer in PL. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3491288]
Magneto-luminescence of quasi-zero dimensional In0.25Ga0.75As/GaAs quantum dots
(1998-12-01)
Cheng, HH
;
Nicholas, RJ
;
Priest, A
;
Tsai, FY
;
Lee, CP
We report photoluminescence measurements on In0.25Ga0.75As/GaAs quantum well and dots grown on (1 1 1)B GaAs substrate in high magnetic fields up to 45 Tesla. A well-defined PL line with full width at half maximum of approximately 5.5 meV is observed. From an analysis of the zero field transition energy, we point out the importance of an internal piezoelectric field. By analyzing the diamagnetic shift of the PL in both Faraday and Voigt configurations, the optical characteristics of a quasi-zero dimensional exciton are discussed. (C) 1998 Elsevier Science B.V. All rights reserved.
Photoluminescence study of high-quality InGaAs/GaAs quantum dots on (111)B GaAs substrates
(1999-01-01)
Tsai, FY
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We present a simple in situ method to fabricate high-quality InGaAs/GaAs quantum dots on (111)B GaAs substrates. The mechanism of the quantum dot formation is not strain relaxation but the growth characteristic of (111)B GaAs under low substrate temperatures. When the growth is performed at low temperatures, the layer-by-layer growth mode is replaced by island growth and therefore quantum dots are formed. The formation of the quantum dots was verified by atomic force microscope (AFM) images and the shift of photoluminescence (PL). The PL emission from the quantum dots was very strong and the full-width at half-maximum (FWHM) of the emission peak was as small as 7.7 meV, indicating excellent quality and very uniform dot formation. The effect of nominal thickness on the quantum dot formation has been investigated.

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