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25 May 2009

Volume 94, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 213101 (2009); http://dx.doi.org/10.1063/1.3139865 (3 pages)

Chul-Ho Lee, Jinkyoung Yoo, Young Joon Hong, Jeonghui Cho, Yong-Jin Kim, Seong-Ran Jeon, Jong Hyeob Baek, and Gyu-Chul Yi
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The impact of intermediate reflectors on light absorption in tandem solar cells with randomly textured surfaces

C. Rockstuhl, F. Lederer, K. Bittkau, T. Beckers, and R. Carius

Appl. Phys. Lett. 94, 211101 (2009); http://dx.doi.org/10.1063/1.3142421 (3 pages) | Cited 11 times

Online Publication Date: 26 May 2009

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The impact of dielectric intermediate reflectors on the light absorption in the top cell of an a-Si:H/μc-Si:H tandem solar cell comprising randomly textured surfaces was investigated by rigorous diffraction theory. Despite the strong light scattering, we found Fabry–Pérot oscillations for the absorption with a decreasing modulation for an increasing thickness of the intermediate layer, a larger oscillation period when compared to thin films and a homogenization of the absorption profile. Optimized intermediate reflectors generate an absorption enhancement in the a-Si:H film, which varies between a factor of 2 and more than 3 for wavelengths of strong and weak absorption, respectively.
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84.60.Jt Photoelectric conversion
42.25.Bs Wave propagation, transmission and absorption

Direct measurements of the nonlinear index of refraction of water at 815 and 407 nm using single-shot supercontinuum spectral interferometry

Z. W. Wilkes, S. Varma, Y.-H. Chen, H. M. Milchberg, T. G. Jones, and A. Ting

Appl. Phys. Lett. 94, 211102 (2009); http://dx.doi.org/10.1063/1.3142384 (3 pages) | Cited 3 times

Online Publication Date: 27 May 2009

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Single-shot supercontinuum spectral interferometry was used to measure the nonlinear index of refraction due to the optical Kerr effect in water at both 815 and 407 nm, with pump pulse lengths of ∼ 90 and ∼ 250 fs, respectively. Knowledge of the nonlinear index at 407 nm allows pulse tailoring to achieve remote underwater pulse compression and self-focusing.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
92.10.-c Physical oceanography
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Donor-related cathodoluminescence of p-AlGaN electron blocking layer embedded in ultraviolet laser diode structure

Rui Li, Jingming Zhang, Li Chen, Huabo Zhao, Ziwen Yang, Tao Yu, Ding Li, Zhicheng Liu, Weihua Chen, Zhijian Yang, Guoyi Zhang, Zizhao Gan, Xiaodong Hu, Qiyuan Wei, Ti Li, et al.

Appl. Phys. Lett. 94, 211103 (2009); http://dx.doi.org/10.1063/1.3143606 (3 pages)

Online Publication Date: 27 May 2009

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Donor-related cathodoluminescence of p-Al0.11Ga0.89N electron blocking layer (EBL) embedded in a laser structure was investigated by low-energy e-beam scanning along the ridge of a vertical taper both at 82 and 300 K. When e-beam probed the close vicinity of multiquantum well from p-side, an emission at 3.313 eV only appeared at 82 K and represented a prominent increase in intensity with a blueshift up to 23 meV. Besides, its intensity exhibited a linear dependence on quantum well (QW) emission intensity at low QW excitation and a sublinear dependence at high QW excitation. Combined with the annealing behaviors of the emission at elevated temperatures, these results were ascribed to the EBL capture of the holes tunneling from neighboring QW under built-in junction field and the subsequent donor-acceptor pairs transition involving a donor level of 116 meV below conduction band, which was presumably related to nitrogen vacancy (VN).
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78.67.De Quantum wells
78.60.Hk Cathodoluminescence, ionoluminescence
68.65.Fg Quantum wells
61.72.Cc Kinetics of defect formation and annealing
61.72.jd Vacancies
73.21.Fg Quantum wells

A large aperture electro-optic deflector

A. Bosco, S. T. Boogert, G. E. Boorman, and G. A. Blair

Appl. Phys. Lett. 94, 211104 (2009); http://dx.doi.org/10.1063/1.3144274 (3 pages)

Online Publication Date: 28 May 2009

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An electro-optic laser beam deflector with a clear optical aperture of 8.6 mm has been designed, realized, and tested. The electro-optic material used to implement the device was a MgO:LiNbO3 crystal. The exceptionally large aperture makes the device suitable for applications where fast scanning of high power laser beams is needed. The measured deflection angle was 120 μrad/kV for a total length of electro-optic material of 90 mm. A mode quality analysis of the laser beam revealed that the M2 of the laser is affected by less than 4% during scan operation when maximum driving voltage is applied.
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42.79.Fm Reflectors, beam splitters, and deflectors
42.79.Ag Apertures, collimators
42.70.-a Optical materials
42.15.Eq Optical system design
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Integrated quantum cascade laser-modulator using vertically coupled cavities

J. Teissier, S. Laurent, C. Sirtori, H. Debrégeas-Sillard, F. Lelarge, F. Brillouet, and R. Colombelli

Appl. Phys. Lett. 94, 211105 (2009); http://dx.doi.org/10.1063/1.3138779 (3 pages) | Cited 1 time

Online Publication Date: 28 May 2009

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We demonstrated an integrated three terminal device able to modulate the cavity losses of quantum cascade lasers. By growing asymmetric doped quantum wells coupled to the laser’s mode an absorption peak can be electrically shifted in and out the laser transition. The use of three terminals allows one to drive the laser independently from the wells and therefore to modulate the laser’s amplitude with an electrical power of only a few milliwatts. This is far less than the power needed for a direct modulation of the laser light.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes

Polarization sensitive terahertz time-domain spectroscopy for birefringent materials

LiangLiang Zhang, Hua Zhong, Chao Deng, CunLin Zhang, and YueJin Zhao

Appl. Phys. Lett. 94, 211106 (2009); http://dx.doi.org/10.1063/1.3143613 (3 pages) | Cited 9 times

Online Publication Date: 28 May 2009

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We present a polarization sensitive terahertz detection method which is able to measure both orthogonal components of the terahertz electric field. It allows for the study of polarization dependent properties of materials. Azimuthal angle dependent transmittance in 0.2–2.6 THz frequency region for crystalline quartz is measured. Polarized terahertz transmission spectroscopy shows that birefringence can result in transmission minima. This work suggests that polarization sensitive detection is effective for removing fake absorption features caused by material birefringence.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
78.20.Fm Birefringence

Electric field dependent radiative decay kinetics of polar InGaN/GaN quantum heterostructures at low fields

Emre Sari, Sedat Nizamoglu, In-Hwan Lee, Jong-Hyeob Baek, and Hilmi Volkan Demir

Appl. Phys. Lett. 94, 211107 (2009); http://dx.doi.org/10.1063/1.3142386 (3 pages) | Cited 4 times

Online Publication Date: 29 May 2009

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Electric field dependent photoluminescence decay kinetics and its radiative component are studied in polar InGaN/GaN quantum heterostructures at low fields. Under externally applied electric field lower than polarization fields, spectrally and time resolved photoluminescence measurements are taken to retrieve internal quantum efficiencies and carrier lifetimes as a function of the applied field. Subsequently, relative behavior of radiative recombination lifetimes is obtained in response to the applied field. In these characterizations of polar InGaN/GaN structures, we observe that both the carrier lifetime and the radiative recombination lifetime decrease with increasing external electric field, with the radiative component exhibiting weaker field dependence.
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78.55.Cr III-V semiconductors
78.47.jd Time resolved luminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Analytical rates determinations and simulations on diffusion and reaction processes in holographic photopolymerization

Dejin Yin, Haihui Pu, Bin Gao, Hongyue Gao, Haitao Dai, and Jianhua Liu

Appl. Phys. Lett. 94, 211108 (2009); http://dx.doi.org/10.1063/1.3133863 (3 pages) | Cited 4 times

Online Publication Date: 29 May 2009

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An analytical method is proposed to determine the initial diffusion and reaction coefficients for monomer molecules in holographic photopolymerization processes. Those parameters can be obtained directly from the measured first order diffraction efficiency at the onset stage in the formation of volume Bragg gratings. Simulations, according to these parameters, on the evolution of the diffraction efficiency, based on one-dimensional reaction-diffusion model, were well consistent with experimental data in our trimethylolpropane triacrylate based monomer and liquid crystal composite material. It is shown that diffusion and reaction both play important roles in postcuring process.
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82.35.-x Polymers: properties; reactions; polymerization
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
66.30.-h Diffusion in solids
61.30.-v Liquid crystals
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