| 1. |
- Gratz, M, et al.
(författare)
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Time-gated x-ray tomography
- 1998
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 73:20, s. 2899-2901
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Tidskriftsartikel (refereegranskat)abstract
- Time-gated x-ray tomography with scatter reduction is demonstrated using a laser-produced plasma as an ultrashort-pulse x-ray source in combination with a time-resolving streak-camera detector. Backprojections of a phantom imbedded in 9 cm of water show an effective 50% increase in contrast when scattered x-ray quanta (being delayed in time) are suppressed by gating on the prompt, nonscattered photons. Implications for future volumetric tomography, in particular concerning possible dose reductions, are discussed. (C) 1998 American Institute of Physics. [S0003-6951(98)02846-0].
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| 2. |
- Haverkort, JEM, et al.
(författare)
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Design of composite InAsP/InGaAs quantum wells for a 1.55 mu m polarization independent semiconductor optical amplifier
- 1999
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 75:18, s. 2782-2784
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Tidskriftsartikel (refereegranskat)abstract
- We investigate a composite InAsP/InGaAs quantum well in which an 8 nm tensile strained InGaAs well is surrounded by two compressively strained InAsP layers which feature a 70:30 conduction band offset ratio. The composite quantum well is found to provide a high TM differential gain. The InAsP layers provide strain compensation while simultaneously shifting the band gap to the relevant 1.55 mu m wavelength region and increasing the electron confinement. Composite InAsP/InGaAs quantum wells are a promising candidate for realizing a polarization independent semiconductor optical amplifier at 1.55 mu m. (C) 1999 American Institute of Physics. [S0003-6951(99)01944-0].
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| 3. |
- Pozina, Galia, et al.
(författare)
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Bound exciton dynamics in GaN grown by hydride vapor-phase epitaxy
- 1999
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 75:26, s. 4124-4126
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Tidskriftsartikel (refereegranskat)abstract
- Temperature-dependent time-resolved photoluminescence measurements were performed on thick GaN layers grown by hydride vapor-phase epitaxy on Al2O3 substrates. Radiative lifetimes were determined for the neutral-donor-bound exciton with position at 3.478 eV and for two neutral-acceptor-bound excitons at 3.473 and 3.461 eV. We report a value of 3600 ps for the radiative lifetime of the acceptor-bound exciton transition at 3.461 eV. The dominant mechanism responsible for the nonradiative recombination of the bound excitons is shown to be connected with dissociation of the bound excitons into free excitons. (C) 1999 American Institute of Physics. [S0003-6951(99)00752-4].
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| 4. |
- Morvan, E, et al.
(författare)
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Channeling implantations of Al+ into 6H silicon carbide
- 1999
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 74, s. 3990-3992
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Tidskriftsartikel (refereegranskat)abstract
- A strong channeling effect of Al+ ions implanted into crystalline SiC has been observed by Monte Carlo simulations and experiments especially designed to demonstrate this phenomenon have been performed. Depth distributions of implanted Al were measured for on- and controlled off-axis Al implantations using secondary ion mass spectrometry (SIMS). Much deeper and wider profiles are obtained for the on-axis implantations as compared to off-axis implants. For higher doses, the experiment also reveals the growth of an intermediate peak slightly deeper than the random peak. The origin of the intermediate peak can be understood by combining SIMS results with Monte Carlo simulations, which motivates the development of advanced simulation tools for the ion implantation process in SiC. (C) 1999 American Institute of Physics. [S0003-6951(99)01426-6].
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| 5. |
- Kemerink, Martijn, et al.
(författare)
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Spectrally resolved luminescence from an InGaAs quantum well induced by an ambient scanning tunneling microscope
- 1999
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 75:23, s. 3656-3658
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Tidskriftsartikel (refereegranskat)abstract
- Spectrally resolved scanning tunneling microscope-induced luminescence has been obtained under ambient conditions, i.e., at room temperature, in air, by passivating the sample surface with sulfur. This passivation turned out to be essential to suppress the local anodic oxidation induced by the tunneling current. From the dependence of the luminescence signal on tunneling current and voltage, we find that the passivation solution and post-passivation annealing temperature strongly modify the surface density of states (SDOS). More specifically, we found evidence that, after annealing at 400 degrees C, no SDOS is left above the bottom of the conduction band. For annealing at 200 degrees C, the SDOS is found to be extended up to 1.0 +/- 0.2 eV above the bottom of the conduction band. In all cases, the passivated (001) surface appears to be completely pinned. (C) 1999 American Institute of Physics. [S0003-6951(99)01949-X].
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| 6. |
- Achtziger, N, et al.
(författare)
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Hydrogen passivation of silicon carbide by low-energy ion implantation
- 1998
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 73, s. 945-947
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Tidskriftsartikel (refereegranskat)abstract
- implantation of deuterium is performed to investigate the mobility and passivating effect of hydrogen in epitaxial alpha-SiC (polytypes 4H and 6H). To avoid excessive damage and the resulting trapping of hydrogen, the implantation is performed with low energy (600 eV H-2(2)+). The H-2 depth profile is analyzed by secondary ion mass spectrometry. Electrical properties are measured by capacitance-voltage profiling and admittance spectroscopy. In p-type SIG, hydrogen diffuses on a mu m scale even at room temperature and effectively passivates accepters. In n-type SiC, the incorporation of H is suppressed and no passivation is detected. (C) 1998 American Institute of Physics.
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| 7. |
- Baranzahi, Amir, et al.
(författare)
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Reversible hydrogen annealing of metal‐oxide‐silicon carbide devices at high temperatures
- 1995
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 67:21, s. 3203-3205
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Tidskriftsartikel (refereegranskat)abstract
- We report on a reversible hydrogen annealing effect observed in platinum-silicon dioxide-silicon carbide structures at temperatures above about 650 degrees C. It appears as a decrease of the inversion capacitance in the presence of hydrogen. This phenomenon is shown to depend on hydrogen atoms, created on the catalytic metal, that pass through the oxide and interact with charge generation sites at the oxide-silicon carbide interface. The consequence of the observation for chemical sensors based on silicon carbide is discussed. The results are phenomenological, since no details of the annealing chemistry could be developed from the present experiments. We find, however, that the annealing process and its reversal have activation energies of about 0.9 eV and 2.9 eV/site,respectively.
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| 8. |
- Berggren, Magnus, et al.
(författare)
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Organic solid-state lasers with imprinted gratings on plastic substrates
- 1998
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 72:4, s. 410-411
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Tidskriftsartikel (refereegranskat)abstract
- Optically pumped laser emission has been observed from thin films of 8-hydroxyquinolinato aluminum (Alq) doped with a DCM dye deposited on a diffraction,orating formed by imprinting a film of BCB with a mold. The BCB film, which is 4 mu m thick, is deposited on a silicon or a flexible plastic substrate. Laser emission occurs at a wavelength war 655 nm which corresponds to the third order of the grating, which has a periodicity of similar to 0.6 mu m. (C) 1998 American Institute of Physics.
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| 9. |
- Berggren, Magnus, et al.
(författare)
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Stimulated emission and lasing in dye-doped organic thin films with Forster transfer
- 1997
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 71:16, s. 2230-2232
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Tidskriftsartikel (refereegranskat)abstract
- Optically pumped stimulated emission and lasing in thin films of an absorbing host 8-hydroxyquinolinato aluminum(Alq) doped with small amounts of the laser dye DCM II is observed. Forster transfer of the excitation from the Alq molecules to the DCM II molecules results in a high absorption coefficient at pump wavelength (337 nm) as well as low absorption loss at the emission wavelengths (610-650 nm). (C) 1997 American Institute of Physics.
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| 10. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Effect of growth temperature on photoluminescence of GaNAs/GaAs quantum well structures
- 1999
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 75:24, s. 3781-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of growth temperature on the optical properties of GaAs/GaNxAs1-x quantum wells is studied in detail using photoluminescence (PL) spectroscopies. An increase in growth temperature up to 580 °C is shown to improve the optical quality of the structures, while still allowing one to achieve high (>3%) N incorporation. This conclusion is based on: (i) an observed increase in intensity of the GaNAs-related near-band-edge emission; (ii) a reduction in band-edge potential fluctuations, deduced from the analysis of the PL line shape; and (iii) a decrease in concentration of some extended defects detected under resonant excitation of the GaNAs. The thermal quenching of the GaNAs-related PL emission, however, is almost independent of the growth temperature and is attributed to a thermal activation of an efficient nonradiative recombination channel located in the GaNAs layers.
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