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| 3. |
- Goss, J.P., et al.
(författare)
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First principles studies of H in diamond
- 2001
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 186:2, s. 263-8
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio methods are used to investigate hydrogen defects in diamond. For the isolated impurity, the bond-centered site is found lowest in energy and posses both donor and acceptor levels. The neutral defect possesses a single local mode with very small infrared effective charge, but the effective charge for the negative charge state is much larger. H+ is calculated to be very mobile with a low activation barrier. Hydrogen dimers are stable as H*2 defects which are also found to be almost IR-inactive. The complex between B and H is investigated and the activation energy for the reaction B-H → B - + H+ found to be in rasonable agreement with experiment. Hydrogen is strongly bound to dislocations which, together with H*2, may form part of the hydrogen accumulation layer detected in some plasma studies.
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| 5. |
- Kemerink, Martijn, et al.
(författare)
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Exciton bleaching in p-type single and double quantum wells: The effects of subband occupation and wave function overlap
- 1997
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Ingår i: Physica status solidi. A, Applied research. - : Academic Verlag GMBH. - 0031-8965 .- 1521-396X. ; 164:1, s. 73-76
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Tidskriftsartikel (refereegranskat)abstract
- We have studied exciton unbinding in empty and p-doped single and double quantum wells, using magneto-photoluminescence excitation measurements. The use of p-type heterostructures allows to discriminate unambiguously between exciton bleaching by Coulomb screening and by the Pauli exclusion principle. The groundstate heavy-hole exciton, which experiences both effects, is unbound at hole densities in the range (6 to 11) x 10(15) m(-2). In contrast, the groundstate light-hole and first excited heavy-hole excitons: which only experience Coulomb screening, still have a finite binding energy at these densities. We found that the excitons of excited subbands are far less efficiently screened than those of the light-hole groundstate, due to the lesser overlap of the screening groundstate heavy holes with the excited subbands than with the groundstate light holes.
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| 6. |
- Lloyd Spetz, Anita, et al.
(författare)
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High temperature sensors based on metal-insulator-silicon carbide devices
- 1997
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Ingår i: Physica status solidi. A, Applied research. - : John Wiley & Sons. - 0031-8965 .- 1521-396X. ; 162:1, s. 493-511
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Tidskriftsartikel (refereegranskat)abstract
- High temperature gas sensors based on catalytic metal-insulator-silicon carbide (MISiC) devices are developed both as capacitors and Schottky diodes. A maximum operation temperature of 1000 degrees C is obtained for capacitors based on 4H-SiC, and all sensors work routinely for several weeks at 600 degrees C. Reducing gases like hydrocarbons and hydrogen lower the flat band voltage of the capacitor and the barrier height of the diode. The time constants for the gas response are in the order of milliseconds and because of this good performance the sensors are tested for combustion engine control. For temperatures around 600 degrees C total combustion occurs on the sensor surface and the signal is high for fuel in excess and low for air in excess. At temperatures around 400 degrees C the response is more linear. The high temperature operation causes interdiffusion of the metal and insulator layers in these devices; and this interdiffusion has been studied. At sufficiently high temperatures the inversion capacitance shows different levels for hydrogen free and hydrogen containing ambients, which is suggested to be due to a reversible hydrogen annealing effect at the insulator-silicon carbide interface.
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| 7. |
- Paskov, Plamen, 1959-, et al.
(författare)
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Anisotropy of the free exciton emission in GaN grown on a-plane sapphire
- 2002
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 190:1, s. 75-79
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the anisotropic in-plane strain on the optical response of GaN layers grown on a-plane sapphire is investigated. A splitting of the G5 states of the A and B free excitons into two components, polarized parallel and perpendicular to the strain direction, is observed. The experimental results are discussed in the framework of the effective exciton Hamiltonian formalism.
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| 8. |
- Jones, R, et al.
(författare)
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Interaction of oxygen with threading dislocations in GaN
- 1999
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 171:1, s. 167-173
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Tidskriftsartikel (refereegranskat)abstract
- A review is given of the results of first principles calculations used to investigate the structures and electronic properties of screw and edge dislocations in GaN. The atoms at the core of the full core screw dislocation possess heavily strained bonds leading to deep gap states. Removing the first shell of Ga and N atoms gives a screw dislocation with a small open core consisting of {101-0} type surfaces. Therefore open-core screw dislocations induce only shallow gap states. In the same way we found the core of the threading edge dislocation to be reconstructed without any deep states. The interaction of oxygen with the cores of open-core screw and edge dislocations is considered and it is found that the impurity has a strong tendency to be bound by Ga vacancies leading to three types of defect trapped in the strain field. We suggest that the most stable defect leads to a poisoning of growth centres on the walls of nanopipes.
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| 10. |
- Arwin, Hans, et al.
(författare)
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Gas sensing based on ellipsometric measurement on porous silicon
- 2003
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Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 197:2, s. 518-522
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Ellipsometry has sufficient sensitivity for sensor applications and is here used as an optical readout method in a gas sensing system. Porous silicon is used as sensing layers in which vapors of solvents can adsorb and condensate due to capillary effects. A miniaturized multi-beam ellipsometer system is proposed and the concept is demonstrated by measurements on alcohol vapors. Optimization of the sensor system is discussed and improvement of sensitivity and alteration of selectivity by metal deposition in porous silicon layers are presented.
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