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19 May 2008

Volume 92, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 202101 (2008); http://dx.doi.org/10.1063/1.2927379 (3 pages)

Jasmin Aghassi, Matthias H. Hettler, and Gerd Schön
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Room temperature terahertz quantum cascade laser source based on intracavity difference-frequency generation

Mikhail A. Belkin, Federico Capasso, Feng Xie, Alexey Belyanin, Milan Fischer, Andreas Wittmann, and Jérôme Faist

Appl. Phys. Lett. 92, 201101 (2008); http://dx.doi.org/10.1063/1.2919051 (3 pages) | Cited 37 times

Online Publication Date: 19 May 2008

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We report on our progress in the development of a terahertz quantum cascade laser source based on intracavity terahertz difference-frequency mixing in a dual-wavelength mid-infrared quantum cascade laser with the active region engineered to possess giant second-order nonlinear susceptibility. In this letter, we demonstrate devices that operate in mid-infrared at λ1 = 8.9 μm and λ2 = 10.5 μm and produce terahertz output at λ ≈ 60 μm via difference-frequency generation with 7 μW output power at 80 K, 1 μW output at 250 K, and still approximately 300 nW output at 300 K.
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42.55.Px Semiconductor lasers; laser diodes
42.65.An Optical susceptibility, hyperpolarizability

Enhancing visibility and resolution in Nth-order intensity correlation of thermal light

De-Zhong Cao, Jun Xiong, Su-Heng Zhang, Lu-Fang Lin, Lu Gao, and Kaige Wang

Appl. Phys. Lett. 92, 201102 (2008); http://dx.doi.org/10.1063/1.2919719 (3 pages) | Cited 25 times

Online Publication Date: 19 May 2008

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The arbitrary Nth-order intensity correlation measurement with thermal light is both theoretically and experimentally investigated. In a double-slit interference scheme with thermal light, we compare the results for higher- and lower-order intensity correlation and demonstrate that the visibility of the interference pattern can be dramatically enhanced while the resolution can also be improved when the order N becomes larger. The experimental results are in agreement with our theoretical analysis.
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42.25.Hz Interference
42.25.Fx Diffraction and scattering
06.30.-k Measurements common to several branches of physics and astronomy

0.3 V drive voltage GaAs/AlGaAs substrate removed Mach–Zehnder intensity modulators

JaeHyuk Shin, Yu-Chia Chang, and Nadir Dagli

Appl. Phys. Lett. 92, 201103 (2008); http://dx.doi.org/10.1063/1.2931057 (3 pages) | Cited 3 times

Online Publication Date: 19 May 2008

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Push-pull driven Mach–Zehnder intensity modulators with a record low drive voltage of 0.3 V were realized in substrate removed very compact GaAs/AlGaAs optical waveguides at 1.55 μm. The modulator electrode is 7 mm long, corresponding to a drive voltage length product of 0.21 V cm. The modulation is due to linear electro-optic and carrier depletion effects and has a high speed potential. The propagation loss was 8 dB/cm, making moderately long devices possible.
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42.79.Hp Optical processors, correlators, and modulators
42.82.Et Waveguides, couplers, and arrays
07.60.Ly Interferometers

Gigahertz quantum key distribution with InGaAs avalanche photodiodes

Z. L. Yuan, A. R. Dixon, J. F. Dynes, A. W. Sharpe, and A. J. Shields

Appl. Phys. Lett. 92, 201104 (2008); http://dx.doi.org/10.1063/1.2931070 (3 pages) | Cited 34 times

Online Publication Date: 19 May 2008

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We report a demonstration of quantum key distribution (QKD) at gigahertz clock rates with InGaAs avalanche photodiodes (APDs) operating in a self-differencing mode. Such a mode of operation allows detection of extremely weak avalanches so that the detector afterpulse noise is sufficiently suppressed. The system is characterized by a secure bit rate of 2.37 Mbit/s at 5.6 km and 27.9 kbit/s at 65.5 km when the fiber dispersion is not compensated. After compensating the fiber dispersion, the QKD distance is extended to 101 km, resulting in a secure key rate of 2.88 kbit/s. Our results suggest that InGaAs APDs are very well suited to gigahertz QKD applications.
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03.67.Dd Quantum cryptography and communication security
85.60.Dw Photodiodes; phototransistors; photoresistors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Comparative study of electroabsorption in InGaN/GaN quantum zigzag heterostructures with polarization-induced electric fields

Emre Sari, Tuncay Ozel, Aslı Koc, Jin-Woo Ju, Haeng-Keun Ahn, In-Hwan Lee, Jong-Hyeob Baek, and Hilmi Volkan Demir

Appl. Phys. Lett. 92, 201105 (2008); http://dx.doi.org/10.1063/1.2931696 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2008

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We present a comparative study on InGaN/GaN quantum zigzag structures embedded in p-i-n diode architecture that exhibit blue-shifting electroabsorption in the blue when an electric field is externally applied to compensate for the polarization-induced electric field across the wells. With the polarization breaking their symmetry, the same InGaN/GaN quantum structures redshift their absorption edge when the external field is applied in the same direction as the well polarization. Both computationally and experimentally, we investigate the effects of polarization on electroabsorption by varying compositional content and structural parameters and demonstrate that electroabsorption grows stronger with weaker polarization in these multiple quantum well modulators.
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85.30.Kk Junction diodes
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors

Systematic investigation of InAs/InP quantum-dash based lasers under external optical feedback

S. Azouigui, B. Dagens, F. Lelarge, A. Accard, D. Make, O. Le Gouezigou, K. Merghem, A. Martinez, Q. Zou, and A. Ramdane

Appl. Phys. Lett. 92, 201106 (2008); http://dx.doi.org/10.1063/1.2931703 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2008

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The tolerance to optical feedback of InAs/InP quantum dash-based lasers is reported for several structures exhibiting differing values of the linewidth enhancement factor and damping factor. An analysis of the onsets of coherence collapse is carried out based on the experimental dynamic parameters extracted for each structure. It is shown that the relevant significant parameter to explain the optical feedback tolerance for this low dimensional material system is the differential gain.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Band structure of terahertz metallic photonic crystals with high metal filling factor

Benjamin Reinhard, Garik Torosyan, and René Beigang

Appl. Phys. Lett. 92, 201107 (2008); http://dx.doi.org/10.1063/1.2929376 (3 pages) | Cited 1 time

Online Publication Date: 22 May 2008

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The excitation of resonant eigenmodes in two-dimensional metallic photonic crystals by incident terahertz pulses is both experimentally and numerically investigated. Transmission experiments are in excellent agreement with numerical calculations of the crystals’ photonic band structures and internal electromagnetic field patterns. The structures show large photonic band gaps in the terahertz spectral range and are highly polarization selective. At the resonant frequencies, transmittance is extraordinarily high despite the high metal filling factor.
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42.70.Qs Photonic bandgap materials
78.70.Gq Microwave and radio-frequency interactions

Room temperature terahertz emission from grating coupled two-dimensional plasmons

Y. M. Meziani, H. Handa, W. Knap, T. Otsuji, E. Sano, V. V. Popov, G. M. Tsymbalov, D. Coquillat, and F. Teppe

Appl. Phys. Lett. 92, 201108 (2008); http://dx.doi.org/10.1063/1.2919097 (3 pages) | Cited 20 times

Online Publication Date: 22 May 2008

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Room temperature terahertz (far infrared) radiation emission from double grating coupled GaInAs/AlGaAs/GaAs heterojunctions is reported. Theoretical calculations of plasmon absorption spectrum are performed using a first principles electromagnetic approach. They correctly reproduce the frequency range and overall shape of the main (broad-band) part of the experimental spectra. The results clearly indicate that important part of the observed room temperature terahertz emission spectra can be due to the radiative decay of hot two-dimensional plasmons in the grating structure.
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78.70.Gq Microwave and radio-frequency interactions
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.30.+q High-frequency effects; plasma effects
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.63.-b Electronic transport in nanoscale materials and structures
42.79.Dj Gratings

Energy transfer and enhanced luminescence in metal oxide nanoparticle and rare earth codoped silica

Neng Wan, Jun Xu, Tao Lin, Xiangao Zhang, and Ling Xu

Appl. Phys. Lett. 92, 201109 (2008); http://dx.doi.org/10.1063/1.2936842 (3 pages) | Cited 12 times

Online Publication Date: 22 May 2008

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A significant enhancement of photoluminescence from Eu3+ embedded in SiO2 matrix is observed by codoping with wide band-gap In2O3 nanoparticles. The enhanced photoluminescence characteristics are strongly influenced by the postannealing temperature and the In3+ concentration. Synchronous scanning photoluminescence technique was used to understand the excitation and luminescence behavior in codoped silica films. Based on the experimental results, we argue that the enhancement of photoluminescence is associated with the effective energy transfer process from In2O3 nanoparticles to the charge transfer band of O2+–Eu3+ instead of the direct transfer to the rare-earth energy levels.
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78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.72.Cc Kinetics of defect formation and annealing
61.72.up Other materials
81.40.Gh Other heat and thermomechanical treatments

Interband dot-to-well transitions in InAs/InGaAs dots in a well probed via photocurrent and electroluminescence spectroscopy

M. Defensor, V. Magusara, E. Estacio, C. Mateo, A. Somintac, and A. Salvador

Appl. Phys. Lett. 92, 201110 (2008); http://dx.doi.org/10.1063/1.2936082 (3 pages)

Online Publication Date: 23 May 2008

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Hole states of InAs/InGaAs dots in a well are optically probed by observing interband–quantum well (QW)–quantum dot (QD) transitions through photocurrent and electroluminescence (EL) spectroscopy. We find multiple sharp peaks with spacing in the range of 10–20 meV in between the expected QD and the QW signals. The spacing and the observed temperature dependent EL suggest that the features are brought about by transitions between the QW electron ground state and the QD hole states. The data extracted from these transitions provide experimental values for the QD hole confinement energies, which can potentially aid in the verification of theoretical models in QD structures.
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73.21.La Quantum dots
73.21.Fg Quantum wells
78.67.De Quantum wells
78.67.Hc Quantum dots
73.63.Kv Quantum dots
73.63.Hs Quantum wells

Wavelength selective coupler with vertical gratings on silicon chip

Kazuhiro Ikeda, Maziar Nezhad, and Yeshaiahu Fainman

Appl. Phys. Lett. 92, 201111 (2008); http://dx.doi.org/10.1063/1.2936862 (3 pages) | Cited 9 times

Online Publication Date: 23 May 2008

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We propose a wavelength selective coupler using vertical grating structure on silicon chip and discuss the operation principle and the analytic design procedure. The transmission spectra expected by the procedure agree with finite difference time domain simulation results. We then fabricate the designed wavelength selective coupler and demonstrate the expected operation. The available wavelength-division-multiplexing bandwidth of this device is not limited by free spectral range as in ring resonators. We also propose some applications of the wavelength selective coupler.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Random lasers with coherent feedback from highly transparent polymer films embedded with silver nanoparticles

Xiangeng Meng, Koji Fujita, Yanhua Zong, Shunsuke Murai, and Katsuhisa Tanaka

Appl. Phys. Lett. 92, 201112 (2008); http://dx.doi.org/10.1063/1.2912527 (3 pages) | Cited 14 times

Online Publication Date: 23 May 2008

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We report on observations of random lasers with coherent feedback in highly transparent polymer films embedded with silver nanoparticles. The hybrid materials were fabricated via in situ synthesis method, through which silver nanoparticles were precipitated by thermal treatment. Sharp peaks with linewidth ∼ 0.5 nm were observed to emerge on the broad emission background when the pump energy reached a threshold, together with unidirectional laser irradiation. Random lasers with coherent feedback induced by silver nanoparticles have been rarely reported, hence, we expect that this work will add an aspect to random lasers by using metal nanostructures to obtain coherent feedback.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems

Collinear second harmonic generations in a nonlinear photonic quasicrystal

Yan Sheng, Kaloian Koynov, Junhong Dou, Boqin Ma, Jingjuan Li, and Daozhong Zhang

Appl. Phys. Lett. 92, 201113 (2008); http://dx.doi.org/10.1063/1.2937210 (3 pages) | Cited 4 times

Online Publication Date: 23 May 2008

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LiNbO3 nonlinear photonic quasicrystal with octagonal symmetry was fabricated. The collinear quasiphase matched second harmonic generations at 22 wavelengths were observed. It is shown that not only the standard type quasiphase matching but also the recently proposed projection-based quasiphase matching plays an important role in these harmonic generations.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Qs Photonic bandgap materials
42.70.Mp Nonlinear optical crystals
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Self-sputtering runaway in high power impulse magnetron sputtering: The role of secondary electrons and multiply charged metal ions

André Anders

Appl. Phys. Lett. 92, 201501 (2008); http://dx.doi.org/10.1063/1.2936307 (3 pages) | Cited 23 times

Online Publication Date: 22 May 2008

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Self-sputtering runaway in high power impulse magnetron sputtering is closely related to the appearance of multiply charged ions. This conclusion is based on the properties of potential emission of secondary electrons and energy balance considerations. The effect is especially strong for materials whose sputtering yield is marginally greater than unity. The absolute deposition rate increases ∼ Q1/2, whereas the rate normalized to the average power decreases ∼ Q−1/2, with Q being the mean ion charge state number.
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81.15.Cd Deposition by sputtering
79.20.Hx Electron impact: secondary emission
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Built-in electric field and large Stokes shift in near-lattice-matched GaN/AlInN quantum wells

G. Franssen, T. Suski, M. Kryśko, A. Khachapuridze, R. Kudrawiec, J. Misiewicz, A. Kamińska, E. Feltin, and N. Grandjean

Appl. Phys. Lett. 92, 201901 (2008); http://dx.doi.org/10.1063/1.2929382 (3 pages) | Cited 6 times

Online Publication Date: 19 May 2008

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Near-lattice-matched GaN/AlInN quantum wells are investigated by means of contactless electroreflectance (CER) and temperature-dependent photoluminescence (PL). Large Stokes shifts, up to 400 meV, between PL peak energies and CER resonances are identified. This Stokes shift is attributed to large potential profile fluctuations (PPFs) in the AlInN barriers. Further evidence for such PPFs and for the additional influence of QW width fluctuations is provided by temperature-dependent PL measurements, demonstrating large PL halfwidths and clear “S-shape” behavior. The influence of a large Stokes shift on the correct determination of the value of the built-in electric field is discussed, and it is shown that PL measurements may lead to a significant overestimation of the built-in electric field in GaN/AlInN QWs.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects

Nonlinear optical properties of Au nanoparticles colloidal system: Local and nonlocal responses

Rogério F. Souza, Márcio A. R. C. Alencar, Eid C. da Silva, Mario R. Meneghetti, and Jandir M. Hickmann

Appl. Phys. Lett. 92, 201902 (2008); http://dx.doi.org/10.1063/1.2929385 (3 pages) | Cited 18 times

Online Publication Date: 19 May 2008

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Z-scan revealed thermal and electronic contributions for the nonlinear refractive index of highly stable colloid containing different concentrations of gold nanoparticles. Large enhancement factors were observed for values of n2 and dn/dT of the colloid, due to the presence of the nanoparticles. Our results suggest that thermal effects will play an important role in the development of photonic applications involving nanostructured materials and in the investigation of nonlocal nonlinear phenomena.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.65.-k Nonlinear optics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.70.Dd Colloids
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Cubic metallic phase of aluminum hydride showing improved hydrogen desorption

R. H. Scheicher, D. Y. Kim, S. Lebègue, B. Arnaud, M. Alouani, and R. Ahuja

Appl. Phys. Lett. 92, 201903 (2008); http://dx.doi.org/10.1063/1.2931083 (3 pages) | Cited 9 times

Online Publication Date: 19 May 2008

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We report on our results calculated from density functional theory and GW of the dehydrogenation properties in a cubic phase of AlH3. The metallic nature of the electronic structure entails a more favorable hydrogen removal energy which is lowered by 75% compared to the insulating hexagonal phase. This remarkable reduction in the Al–H bond strength bears important consequences for feasible applications of AlH3 as an on-board hydrogen storage material for mobile applications. We suggest that the cubic phase could be prepared and stabilized experimentally at ambient pressure by off-board quenching.
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61.66.Fn Inorganic compounds
68.43.Nr Desorption kinetics
71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Measuring local lattice polarity in AlN and GaN by high resolution Z-contrast imaging: The case of (0001) and (1math00) GaN quantum dots

Jean-Luc Rouviere, Catherine Bougerol, Benoit Amstatt, Edith Bellet-Almaric, and Bruno Daudin

Appl. Phys. Lett. 92, 201904 (2008); http://dx.doi.org/10.1063/1.2917449 (3 pages) | Cited 7 times

Online Publication Date: 20 May 2008

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By using a probe Cs corrected transmission electron microscope, the local lattice polarity, i.e., the local stacking of atoms, in AlN and GaN is determined. The N atomic columns are not directly resolved, but determined from the tunnel positions of the structure. The method is first tested on GaN quantum dots grown on polar (0001) AlN surfaces. Then it is applied to GaN quantum dots grown on nonpolar (1math00) AlN surfaces. In the (11math0) plane, (1math00) GaN dots have an asymmetrical shape and grow faster along the +c = [0001] direction than along −c = [000math].
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68.65.Hb Quantum dots (patterned in quantum wells)

Crystal structure and photoluminescence of Mn2+–Mg2+ codoped gamma aluminum oxynitride (γ-AlON): A promising green phosphor for white light-emitting diodes

Rong-Jun Xie, Naoto Hirosaki, Xue-Jian Liu, Takashi Takeda, and Hui-Li Li

Appl. Phys. Lett. 92, 201905 (2008); http://dx.doi.org/10.1063/1.2920190 (3 pages) | Cited 23 times

Online Publication Date: 20 May 2008

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This letter reports on the crystal structure and luminescence of a green gamma aluminum oxynitride phosphor. This phosphor, codoped with Mn2+ and Mg2+, shows a single cubic spinel phase, with Mn2+ and Mg2+ substituting Al3+ in the tetrahedral sites. It shows a broad emission band centered at 520 nm and a full width at half maximum of 44 nm. The green phosphor exhibits a small thermal quenching and high internal quantum efficiency of 62% under the blue light irradiation, enabling it to be used in high color rendering white light-emitting diodes.
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61.66.Fn Inorganic compounds
78.55.Hx Other solid inorganic materials
85.60.Jb Light-emitting devices

Radiative heat transfer between metallic nanoparticles

Pierre-Olivier Chapuis, Marine Laroche, Sebastian Volz, and Jean-Jacques Greffet

Appl. Phys. Lett. 92, 201906 (2008); http://dx.doi.org/10.1063/1.2931062 (3 pages) | Cited 10 times

Online Publication Date: 20 May 2008

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In this letter, we study the radiative heat transfer between two nanoparticles in the near and far fields. We find that the heat transfer is dominated by the electric dipole-dipole interaction for identical dielectric particles and by the magnetic dipole-dipole interaction for identical metallic nanoparticles. We introduce polarizability formulas valid for arbitrary values of the skin depth. While the heat transfer mechanism is different for metallic and dielectric nanoparticles, we show that the distance dependence is the same. However, the dependence of the heat flux on the particle radius is different.
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75.30.Cr Saturation moments and magnetic susceptibilities
73.22.-f Electronic structure of nanoscale materials and related systems
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Anisotropic optical properties of free and bound excitons in highly strained A-plane ZnO investigated with polarized photoreflectance and photoluminescence spectroscopy

Yoon Sung Nam, Sang Wook Lee, K. S. Baek, S. K. Chang, Jae-Ho Song, Jung-Hoon Song, Seok Kyu Han, Soon-Ku Hong, and Takafumi Yao

Appl. Phys. Lett. 92, 201907 (2008); http://dx.doi.org/10.1063/1.2930683 (3 pages) | Cited 15 times

Online Publication Date: 21 May 2008

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We have investigated the polarization dependence of the near-band-edge photoluminescence and photoreflectance spectra in nonpolar (A-plane) ZnO films under strong biaxial compressive strain. We show that anisotropic strain and the orientation of the nonpolar plane play an important role in determining the polarization selectivity and properties of excitonic transitions. We identified four distinct band-edge transitions at 3.449, 3.420, 3.386, and 3.326 eV. They were identified as E2 and E1 free excitons, E1 excitons bound to a donor, and free-electron-to-bound-hole transition, respectively. Unlike previously reported results on relatively thick nonpolar films, the E1 exciton (lowest energy) was mainly polarized to E⊥c and weakly polarized to E∥c under strong biaxial compressive strain in the 100 nm thick film. The E2 exciton (next higher energy) was exclusively polarized to E∥c. The localization energy of DX is 34 meV, which is much larger than that in polar ZnO, and the DX was not thermally delocalized even at room temperature.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.55.Et II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Near optical isotropy in noncubic SrI2: Density functional calculations

D. J. Singh

Appl. Phys. Lett. 92, 201908 (2008); http://dx.doi.org/10.1063/1.2936079 (3 pages) | Cited 9 times

Online Publication Date: 22 May 2008

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We report calculations of the electronic structure and optical properties of orthorhombic SrI2. These were done using the Engel–Vosko generalized gradient approximation. We find that the dielectric function and refractive indices are almost isotropic in this noncubic material. This suggests that low cost nonconventional routes for producing SrI2-based scintillators may be practical and, in particular, that ceramic processing may be used.
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71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
61.66.Fn Inorganic compounds

Crystal and defect chemistry influences on band gap trends in alkaline earth perovskites

Soonil Lee, William H. Woodford, and Clive A. Randall

Appl. Phys. Lett. 92, 201909 (2008); http://dx.doi.org/10.1063/1.2936091 (3 pages) | Cited 9 times

Online Publication Date: 22 May 2008

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A number of perovskites with A-site alkaline earth chemistries being Ca, Sr, and Ba, and tetravalent cations including Ce, Zr, and Ti are measured for optical band gap and found to vary systematically with tolerance factor and lattice volume within limits defined by the chemistry of the octahedral site. This paper also focuses on the BaTiO3 system, considering equilibrated nonstoichiometries, and determines the changes in band gap with respect to Ba/Ti ratios. It was found that the optical band gap changes in the solid solution regime and is invariant in the second phase regions, as would be expected. In the cases of Ba/Ti<1.0, the variation in band gap scales with lattice volume, but in the Ba/Ti>1.0 stoichiometries, there is a distinct Urbach tail and the trend with lattice volume no longer holds. It is inferred that the VTi⁗−2VO•• partial Schottky complex controls the band gap trend with Ba-rich nonstoichiometries.
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61.66.Fn Inorganic compounds
61.66.Bi Elemental solids
61.66.Dk Alloys
71.20.Ps Other inorganic compounds
78.40.Ha Other nonmetallic inorganics
77.80.-e Ferroelectricity and antiferroelectricity
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Cubic GaN/AlN multiple quantum well photodetector

E. A. DeCuir, Jr., M. O. Manasreh, Elena Tschumak, J. Schörmann, D. J. As, and K. Lischka

Appl. Phys. Lett. 92, 201910 (2008); http://dx.doi.org/10.1063/1.2936279 (3 pages) | Cited 8 times

Online Publication Date: 22 May 2008

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Photodetectors based on intersubband transitions in molecular beam epitaxially grown cubic GaN/AlN multiple quantum wells were fabricated and tested. The presence of the intersubband transition was confirmed by using the optical absorption technique for structures with different well widths. Samples were polished into waveguide configuration on which the devices were fabricated. The photoresponse spectra were collected in the temperature range of 77–215 K under the influence of small bias voltages. All devices exhibit photovoltaic effect where the photoresponse is observed at zero bias voltage. Theoretical calculations of the intersubband transition were performed and found to be in agreement with the observed results.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.82.Et Waveguides, couplers, and arrays
42.82.Bq Design and performance testing of integrated-optical systems

Thermodynamic trends in the uptake capacity of porous adsorbents on methane and hydrogen

Anutosh Chakraborty, Bidyut Baran Saha, Shigeru Koyama, Kim Choon Ng, and Seong-Ho Yoon

Appl. Phys. Lett. 92, 201911 (2008); http://dx.doi.org/10.1063/1.2918984 (3 pages) | Cited 1 time

Online Publication Date: 22 May 2008

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A considerable progress has been made for the development of novel porous materials with controlled architectures and surface treatment. An important feature of these adsorbent materials is the maximization of adsorption capacity at Henry’s region. A thermodynamic framework is presented to capture the relationship between the pore specific surface areas with the enthalpy of adsorption. By using this approach, the scientific community can be guided to the development of advanced porous adsorbent and adsorbate pairs. The adsorbents with the highest porous surface areas tend to possess lower isosteric heat of adsorption when storing the methane and hydrogen gases at room temperature.
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82.60.-s Chemical thermodynamics
68.35.Md Surface thermodynamics, surface energies
68.43.Mn Adsorption kinetics
81.65.-b Surface treatments
84.60.-h Direct energy conversion and storage
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