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Optical, magneto-optical and holographic study of Bi4Ge3O12 crystals doped with transition elements
(2006-01-01)
Petkova, Petya
;
Marinova, Vera
;
Iliev, Ilia
;
Dimov, Todor
;
Lin, Shiuan H.
Bismuth germanate Bi3Ge4O12 (BGO) single crystals doped with ruthenium, manganese and ruthenium plus manganese are gown by Czohralski technique with automatically diameter-weight control method. The effect of doping on the light-induced, magneto-optical and holographic properties of BGO single crystals is studied. It was found that the optical transmission spectrum of doped samples is modified strongly under thermal annealing and homogeneous illumination with UV light as well as the photochromic effect is fully reversible. The magneto-optical rotation was measured and Verdet constant was calculated at visible spectral range. Holographic grating are successfully recorded at 633 nm.
Structure-related optical properties of rapid thermally annealed Ba0.7Sr0.3TiO3 thin films
(1999-11-01)
Kuo, YF
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Polycrystalline thin films of Ba0.7Sr0.3TiO3 (BST) are deposited on SiO2/Si substrates by radio frequency magnetron sputtering. This work also examines how the O-2 atmosphere annealing temperature affects not only the crystalline and morphological properties, but also the refractive index and the optical band gap energy. The BST films possess the highest dense packing growth and near-bulk optical properties as the O-2 atmosphere annealing temperature increases. Analysis results indicate that the packing density and the refractive index of BST films increase as the annealing temperature increases, whereas the optical band gap energies apparently decreased. In addition, the dispersion of the refractive index is analyzed in terms of dispersion parameters using the single oscillator dispersion model of Wemple and DiDomentico. (C) 1999 Elsevier Science S.A. All rights reserved.
Optical and electrical investigations of isoelectronic In-doped GaN films
(2000)
Shu, CK
;
Lee, WH
;
Pan, YC
;
Chen, CC
;
Lin, HC
The optical and electrical properties of isoelectronic In-doped GaN films grown by metalorganic vapor phase epitaxy (MOVPE) were investigated by X-ray, photoluminescence (PL), Hall and Raman measurements. As a result, adequate In-doping quantity causes not only a reduction of yellow luminescence and unintentional background concentration, but an enhanced mobility and decrease in the widths. The improved crystalline and optical qualities of GaN films may be attributed to the decrease in defects. (C) 2000 Elsevier Science Ltd. All rights reserved.
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.
Study of linear and nonlinear optical properties of distorted Ti-O-6 perovskite structure in BaxSr1-xTiO3
(2000-06-01)
Chen, WK
;
Cheng, CM
;
Huang, JY
;
Hsieh, WF
;
Tseng, TY
We report the linear and nonlinear optical properties of sol-gel prepared BaxSr1-xTiO3 (BST) crystalline powders. The results from powder X-ray diffraction, birefringence, and second-order optical nonlinearity measurements indicate that the paraelectric-ferroelectric phase transition of Ba0.75Sr0.25TiO3 occurs near room temperature. The second-order optical nonlinearity of the ferroelectric BST is about 7.9 pm/V. The index of refraction, n = 2.2, and birefringence, Delta n(B) similar to 0.05, are also appropriate for practical nonlinear optical applications. (C) 2000 Elsevier Science Ltd. All rights reserved.
InGaAs/GaAs quantum wells and quantum dots on (111)B orientation
(2001)
Tyan, SL
;
Lin, YG
;
Tsai, FY
;
Lee, CP
;
Shields, PA
We report a magneto optical characterization of InGaAs/GaAs quantum well (QW) and quantum dot (QD) structures grown on (111)B GaAs substrates. The photoluminescence (PL) peak shift under high excitation intensity is used to distinguish QW from QD structures together with atomic force microscopy (AFM) imaging, The binding energy in(lll)InGaAs/GaAs QW is about 5 meV, The extent of the wave function obtained from the diamagnetic shift of the PL peak energy is consistent with the result calculated by the k,p method. The InGaAs/GaAs QD lateral confinement energy and the dot size are also estimated from the diamagnetic shift of the PL lines. The lateral confinement energy is estimated as 7 meV. The mean radius of the InGaAs QD is about 14 nm and the dot height is about 6 nm, which is in good agreement with the results as revealed in AFM imaging. (C) 2001 Published by Elsevier Science Ltd.
Luminescence intensity reduction in Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy
(2001-04-01)
Shu, CK
;
Chen, HH
;
Lee, WH
;
Pan, YC
;
Huang, HY
Photoluminescence dynamic responses of a heavily Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy have been investigated. As the probe power density increased from 2.5 to 925 W/cm(2), a Mg-related emission band shifted from 2.82 to 3.16 eV revealing characteristics of donor-acceptor pair recombination. The intensity evolution also showed slow decay that suggests the metastable emission behavior. A simple potential barrier model was proposed to occur between the Mg related deep levels and common Mg acceptor level, which impedes electron relaxation and thus slows down the luminescence decay. From the variation of decay time constant with temperature. a barrier energy was deduced to be about 69 meV which is very close to the electrical result of 68 meV.
Internal stresses and microstructures of commercial thick diamond films deposited by different deposition methods
(2001-11-01)
Kuo, CT
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Wu, JY
;
Lin, CH
;
Lu, TR
;
Sung, CM
Structures and stress state of six commercial freestanding thick diamond films (> 300 mum) were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and Raman spectroscopy. These films represent the typical samples synthesized by three different chemical vapor deposition (CVD) methods, including DC are, microwave plasma, and hot filament. It was found that the higher diamond deposition rate it reaches, the more non-diamond carbons it contains, and the larger the residual compressive stress it possesses. Moreover, the samples with the highest degree of optical transparency are under the lowest compressive stress. These crystal characteristics can be manipulated by selecting different deposition methods and parameters that affect nucleation rate and growth rate of diamond. The present results show that the DC are method gives poorly developed crystals, and its residual compressive stress of the films is the highest due to the fastest diamond nucleation and crystal growth rates. (C) 2001 Elsevier Science B.V. All rights reserved.
Effect of ruthenium doping on the optical and photorefractive properties of Bi12TiO20 single crystals
(2002-03-15)
Marinova, V
;
Hsieh, ML
;
Lin, SH
;
Hsu, KY
;
電子物理學系
Bi12TiO20 (BTO) single crystals nominally pure and doped with ruthenium are grown by top-seeded solution growth method. The effect of ruthenium concentration on optical and photorefractive properties is studied. Strong influence of doping on these properties is observed. It is shown that optical transmission of crystal samples with higher ruthenium content is shifted to the near IR spectral region, while the absorption coefficient is considerably increased. The optical activity of Ru doped crystals is further reduced in comparison with undoped BTO. Photochromic effect is observed in strongly doped crystal. Photorefractive properties are experimentally investigated using two-beam coupling. Response time and diffraction efficiency are changed with ruthenium content. (C) 2002 Elsevier Science B.V. All rights reserved.
Effect of annealing on the structural and optical properties of AgGaS2 thin films prepared by pulsed laser deposition
(2002-11-01)
Hsu, HC
;
Chen, HH
;
Kuo, SY
;
Chang, CS
;
Hsieh, WF
The influence of annealing on the AgGaS2 films groom by pulsed laser deposition has been investigated. The X-ray diffraction results show the AgGaS2 films were found with preferential orientation (1 1 2) normal to the surface and silver droplets,were diminished after the post-annealing. Photoluminescence (PL) measurements reveled the exciton energy is slightly red shifted that is possibly due to the thermal strain effect. The binding energy of the shallow, donors is similar to28 meV determined from temperature dependent PL spectra, In addition, the A-exciton and the B/C-exciton could be observed in the transmittance spectra at room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

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