| 1. |
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| 2. |
- Arwin, Hans, 1950-, et al.
(författare)
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Enhancement in ellipsometric thin film sensitivity near surface plasmon resonance conditions
- 2008
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 205:4, s. 817-820
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Tidskriftsartikel (refereegranskat)abstract
- Ellipsometry used in internal reflection mode exhibits enhanced thin film sensitivity if operated close to surface plasmon resonance conditions. Compared to conventional ellipsometry, the changes in the ellipsometric parameter Δ are several orders of magnitude larger. Here, the origin of this large sensitivity is discussed by analysing thin film approximations of the complex reflectance ratio. It is found that the thickness sensitivity in Δ is proportional to the inverse of the difference between the intrinsic and the radiation-induced damping of the surface plasmons.
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| 3. |
- Blumenau, A.T., et al.
(författare)
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The effect of charge on kink migration at 90° partial dislocations in SiC
- 2005
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:5, s. 877-882
-
Tidskriftsartikel (refereegranskat)abstract
- SiC bipolar devices show a degradation under forward-biased operation which has been linked with a recombination enhanced motion of one of the two glide dislocations having either Si or C core atoms. We have carried out calculations of the core structures and dynamics of partial dislocations in 3C and 2H-SiC using the density functional based codes DFTB and AIMPRO. After in earlier theoretical work we reported on the structure, energetics and electronic activity of both of the Shockley partials, and on the formation and migration barriers of kinks, in this work we present first results on the effect of charge on the disloction kinks. The calculations give insights into the device degradation mechanism.
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| 4. |
- Buyanova, Irina A., et al.
(författare)
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Optical and electronic properties of GaInNP alloys - a new material system for lattice matching to GaAs
- 2008
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 205:1, s. 101-106
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we will review our recent results from optical characterization studies of GaInNP. We will show that N incorporation in these alloys affects their structural and defect properties, as well as the electronic structure. The main structural changes include (i) increasing carrier localization due to strong compositional fluctuations, which is typical for all dilute nitrides, and (ii) N-induced long range ordering effects, specific for GaInNP. The observed degradation of radiative efficiency of the alloys upon increasing N content is attributed to formation of several defects acting as centres of efficient non-radiative recombination. One of the defects is identified as a complex involving a Ga interstitial atom. N incorporation is also found to change the band line up from the type I in the GaInP/GaAs structures to the type 11 in the GaInNP/GaAs heterojunctions with [N] > 0.5%. For the range of N compositions studied ([N] <= 2%), a conduction band offset at the GaInNP/GaAs interface is found to nearly linearly depend on [N] at -0.10 eV/%, whereas the valence band offset remains unaffected. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 5. |
- Carva, Karel, et al.
(författare)
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Spin-mixing conductances : The influence of disorder
- 2008
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Ingår i: Physica status solidi A, Applications and materials science. - : Wiley. - 1862-6300. ; 205:8, s. 1805-1808
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Tidskriftsartikel (refereegranskat)abstract
- Spin transfer torque exerted on a magnetic layer can be viewed as a linear response to the spin accumulation inside an adjacent non-magnetic layer, information about their response coefficient is provided by the complex spin-mixing conductance C-mix. Substitutional disorder is known to affect the spin-dependent charge conductances and often reduces strongly the magnetoresistance. Here, we examine its impact on C-mix of several selected realistic systems. Recently predicted oscillations of C-mix as a function of ferromagnetic layer thickness in Ni based junctions might be suppressed by interface interdiffusion, but presented ab initio calculations disprove this possibility. Halfmetallic character of the Heusler compound Co(2)Mnsi is destroyed by often encountered antisite disorder; however the impact of this disorder to the predicted C-mix is rather weak. Diluted magnetic semiconductor (Ga,Mn)As is an intrinsically disordered system the analysis of calculations shows that the variation of C-mix with substitutional Mn content can be understood in terms of the associated change of the number of carriers, whereas the variation with lattice defects is more complex.
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| 6. |
- Darakchieva, Vanya
(författare)
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Infrared generalized ellipsometry on non-polar and superlattice group-III nitride films : Strain and phonon anisotropy
- 2008
-
Ingår i: Physica Status Solidi (A) Applications and Materials. - : Wiley. - 1862-6300. ; 205:4, s. 905-913
-
Tidskriftsartikel (refereegranskat)abstract
- This contribution reviews the application of generalized infrared spectroscopic ellipsometry (GIRSE) to studies of optical phonons in heteroepitaxial wurtzite GaN films with a-plane orientation and c-plane Al(Ga)N/GaN superlattices. We demonstrate the capability of GIRSE to detect spectrally narrow dichroism, caused by anisotropic strain in non-polar oriented films thereby allowing a precise location of the phonon mode resonances for different polarizations. A distinct correlation between anisotropic strain components, which have been independently asessed by high-resolution X-ray diffraction, and phonon frequencies reveal the phonon deformation potentials. Further, GIRSF is shown to be a valuable tool in identification of superlattice phonon modes and their character. The frequency shifts of the superlattice modes with respect to the strain-free positions are analyzed versus strain and composition in order to assess the mode suitability for estimation of strain, polarization doping, and composition for the individual layers in complex device heterostructures. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.
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| 7. |
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| 8. |
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| 9. |
- Fujita, N., et al.
(författare)
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Core reconstructions of the (100) edge dislocation in single crystal CVD diamond
- 2007
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 204:7, s. 2211-2215
-
Tidskriftsartikel (refereegranskat)abstract
- Dislocations are common defects in both natural as well as in CVD-grown diamond. Recent advances in the growth of high quality single crystal CVD diamond have led to an increased interest in the atomistic and electronic structure of 100 dislocations. These dislocations are observed as mixed-type 45° and pure edge dislocations. Previously we investigated both types and found that the 45° is by far lower in core energy than the proposed structure of the edge type. In this work we focus on the straight 100 dislocation only and present novel core reconstructions. We find a minimum energy structure for the edge-type dislocation which has a similar core energy as the mixed-type dislocation.
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| 10. |
- Fujita, N, et al.
(författare)
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Theoretical studies on 100 dislocations in single crystal CVD diamond
- 2006
-
Ingår i: Physica status solidi A. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; , s. 3070-3075
-
Konferensbidrag (refereegranskat)abstract
- Dislocations are common defects in both natural as well as in CVD-grown diamond. Recent advances in the growth of high quality single crystal CVD diamond have led to an increased interest in the atomistic and electronic structure of < 100 > dislocations. These dislocations are observed as mixed-type 45 degrees and pure edge dislocations. Hence in this work we present ab initio modelling studies on these two types of dislocations. The 45 degrees dislocation is found to be by far more stable than the pure edge and both dislocations lead to states in the electronic band gap. An alternative structure for the mixed-type dislocation, which is not straight but kinked and consists of short edge and screw segments, was found slightly higher in energy than the straight structure.
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| 11. |
- Gabrysch, Markus, et al.
(författare)
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Compensation in boron-doped CVD diamond
- 2008
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Ingår i: Physica status solidi. A, Applications and Materials Science. - : Wiley. - 1862-6300. ; 205:9, s. 2190-2194
-
Tidskriftsartikel (refereegranskat)abstract
- Hall-effect measurements on single crystal boron-doped CVD diamond in the temperature interval 80-450 K are presented together with SIMS measurements of the dopant concentration. Capacitance-voltage measurements on rectifying Schottky junctions manufactured on the boron-doped structures are also presented in this context. Evaluation of the compensating donor (N-D) and acceptor concentrations (N-A) show that in certain samples very low compensation ratios (N-D/N-A below 10(-4)) have been achieved. The influence of compensating donors on majority carrier transport and the significance for diamond device performance are briefly discussed.
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| 12. |
- Gallas, B., et al.
(författare)
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Changes in optical properties of MnAs thin films on GaAs(001) induced by a- to B-phase transition
- 2008
-
Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 205:4, s. 859-862
-
Tidskriftsartikel (refereegranskat)abstract
- MnAs layers with 45 nm thickness were grown epitaxially on GaAs(001) substrates. Ellipsometry measurements were made in the spectral range 0.045 eV to 6 eV as a function of temperature (between –10 °C and 50 °C) at 70° of incidence. In this way the transition from the hexagonal α-phase to the orthorhombic β-phase could be monitored. Non-zero off-diagonal elements of the Jones matrix for an azimuth of 38° off the [10] axis of the substrate indicate that the optical functions of MnAs are anisotropic in both phases. The optical conductivity exhibits low-energy interband transitions around 0.3 eV, more clearly seen in the α-phase than in the β-phase. Extrapolation of the optical conductivity to zero frequency confirms that the α-phase is about two times more conducting than the β-phase. A broad structure is observed in the visible range around 3 eV. The α-phase is characterised by an anisotropy induced energy difference of this structure with a maximum at 2.8 eV for the extraordinary index and at 3.15 eV for the ordinary index. This difference vanishes in the β-phase in which anisotropy mainly induces changes in amplitude of the 3 eV structure. The assignment of the structures will be discussed.
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| 13. |
- Gallas, B., et al.
(författare)
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Monitoring the a to B-phase transition in MnAs/GaAs(001) thin films as funcion of temperature
- 2008
-
Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 205:4, s. 863-866
-
Tidskriftsartikel (refereegranskat)abstract
- MnAs layers with a 5 nm thick amorphous GaAs capping layer were grown epitaxially on GaAs(001). Generalized ellipsometric measurements were made on a 45 nm thick layer in the spectral range 1.5–4 eV at temperatures between –10 °C and 50 °C in steps of 5 °C. By using both the diagonal and off-diagonal elements of the Jones matrix, the in-plane unixial anisotropy of MnAs was determined in terms of the ordinary and extraordinary complex dielectric functions. The measurements at each temperature could be well reproduced by modeling using the optical properties of the two limiting phases α-MnAs and β-MnAs determined at –10 °C and 50 °C, respectively. The best sensitivity to the volume fractions of the two phases was obtained near 2.2 eV by monitoring the generalized ellipsometric parameter Δp for which the variations reached 30°.
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| 14. |
- Haratizadeh, H, et al.
(författare)
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Effects of Si doping position on the emission energy and recombination dynamics of GaN/AlGaN multiple quantum wells
- 2006
-
Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 203:1, s. 149-153
-
Tidskriftsartikel (refereegranskat)abstract
- We report results from detailed optical spectroscopy from MOCVD grown GaN/Al0.07Ga0.93N multiple quantum wells (MQWs). Effects of Si doping position on the emission energy and recombination dynamics were studied by means of photoluminescence (PL) and time-resolved PL measurements. The samples were Si doped with the same level but different position of the dopant layer. Only the sample doped in the well shows the MQW emission redshifted compare to the GaN bandgap. The redshift is attributed to the self-energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. At low temperature the PL decay time of the sample doped in the well by a factor of two is longer than for the barrier doped case. The difference is explained by the effect of interplay of free carriers and ions on the screening of the polarization field in these doped structures.
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| 15. |
- Hounsome, L.S., et al.
(författare)
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Optical properties of vacancy related defects in diamond
- 2005
-
Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:11, s. 2182-2187
-
Tidskriftsartikel (refereegranskat)abstract
- ‹110› vacancy chains, multi-vacancy clusters and vacancy discs have been modeled using density functional theory within the AIMPRO and DFTB codes. While a connection can be established between the results on vacancy chains and previous EPR experiments, no connection can be made between the point defects and the optical properties of natural type IIa brown diamonds. However, a vacancy disc consisting of a {111} double plane of vacancies is stable and possesses an absorption spectrum similar to that found in brown diamonds.
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| 16. |
- Iusan, Diana, et al.
(författare)
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Role of defects on the magnetic interactions in Mn-doped ZnO
- 2007
-
Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 204:1, s. 53-60
-
Tidskriftsartikel (refereegranskat)abstract
- Oxide based diluted magnetic semiconductors are highly controversial from the point of view of intrinsic ferromagnetism brought in by doping with transition metal ions. By ab-initio Korringa-Kohn-Rostoker-Coherent-Potential-Approximation (KKR-CPA) calculations in the framework of density functional theory, we have obtained the electronic structure and magnetic exchange interaction parameters of Mn-doped ZnO in the presence and absence of several types of defects. A weak antiferromagnetic exchange interaction is observed in pure Mn-doped ZnO in the dilute limit with an increase in the strength of interactions with increasing concentration of Mn. In the presence of donor defects, such as oxygen vacancies and interstitial Zn, the interactions remain antiferromagnetic whereas in case of acceptor defects like Zn vacancies and N substitution of O, ferromagnetic interactions are observed. We have used the ab-initio exchange parameters in Monte-Carlo simulations for calculating finite temperature properties. Due to the short ranged behavior of interactions and disorder effects, the Curie temperatures calculated from Monte Carlo simulations show moderate values, not exceeding 50 K when the Mn content is 5%.
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| 17. |
- Jaafar, M., et al.
(författare)
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FePt thin film irradiated with high energy ions
- 2007
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Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 204:6, s. 1724-1730
-
Tidskriftsartikel (refereegranskat)abstract
- The changes in structural and magnetic properties of FePt thin films due to the irradiation with high energy ions (Br7+ and Cl2+) were studied. From the hysteresis loops dominating in-plane anisotropy is derived, however, the samples present a minor out-of-plane component. The structure and the magnetic properties of the films can be tuned by selecting the appropriate irradiation parameters (different ions, energies and fluencies). For the irradiation parameters used in this study an in-plane anisotropy is favoured. Irradiation with Br7+ seems to induce minor changes in the structural ordering of the thin films, whereas the Cl2+ ions promote the amorphization of the surface of the films. In addition, a magnetic thin film pattemed at the micrometer scale was obtained after irradiation through a micrometric mask.
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| 18. |
- Jones, Robert, et al.
(författare)
-
Electrical and optical properties of multivacancy centres in diamond
- 2007
-
Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 204:9, s. 3059-3064
-
Tidskriftsartikel (refereegranskat)abstract
- Recent experiments have shown that vacancy clusters are common defects in all types of monocrystalline brown diamond. This is believed to be due to an enhanced stability of the bounding (I 11) or (I 10) surfaces, arising from the formation of pi-bonded chains. These chains lead to broad bands of gap states with acceptor and donor levels around E-v + 2 eV. They also are likely to be responsible for the broad absorption continuum extending from the NIR through the visible and into the UV region which is characteristic of brown diamonds. High temperature treatment removes or transforms the clusters in CVD and type IIa diamonds leaving the diamond colourless. In type la brown diamonds, heat treatments up to 2500 degrees C lead to the breakup of the clusters and the formation of specific vacancy-nitrogen defects. We show that ab initio modelling of the interaction of nitrogen with the chains open a gap and leads to a threshold absorption energy in the 1-2 eV range. Finally, the calculations shed light on the identity of the vacancy-nitrogen defects observed.
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| 19. |
- Kakanakova-Georgieva, Anelia, et al.
(författare)
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Hot-wall MOCVD grown homoepitaxial GaN layers with intense intrinsic excitonic structure
- 2005
-
Ingår i: Phys. Stat. Sol. (a), Vol. 202. - : Wiley. ; , s. 739-743
-
Konferensbidrag (refereegranskat)abstract
- We report on a new approach to MOCVD growth of GaN, i.e. hot-wall MOCVD, and its application to homoepitaxy on GaN substrates. The quality of the epilayers is examined by photoluminescence (PL). Homoepitaxially hot-wall MOCVD grown GaN layers show (1) intense PL free-exciton emissions relative to the intensity of the principal bound-exciton emission and (2) homogeneous cathodoluminescence emission within the terraces developed during the step-flow growth. Impurity concentrations in the material are measured by secondary ion mass spectrometry (SIMS). (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 20. |
- Khranovskyy, Volodymyr, et al.
(författare)
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Investigation of ZnO as a perspective material for photonics
- 2008
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 205:1, s. 144-149
-
Tidskriftsartikel (refereegranskat)abstract
- Emissive properties of ZnO are of great interests in terms of the UV LED device design. The persistent "green" luminescence due to deep defect is an obstacle for obtaining an intense UV emission, expected from ZnO. We report the positive role of thermally diffused H toward quenching the defect emission in ZnO. It is suggested that hydrogen passivates defects responsible for DLE, resulting in efficient near band edge luminescence. As-grown ZnO/SiNx :H/Si films, deposited at 350 degrees C demonstrate intense narrow peaks of UV emission at 380 nm and a ratio of emission intensities, NBE/DLE approximate to 42. [GRAPHICS]
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| 21. |
- Lozovik, Yu E, et al.
(författare)
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Coherent phases and magnetoexcitons in graphene
- 2009
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Ingår i: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE. - : Wiley. - 1862-6300. ; 206:5, s. 927-930
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Tidskriftsartikel (refereegranskat)abstract
- Unique band structure peculiarities of graphene imply that near Fermi level electrons are described by two-dimensional Dirac equation for massless particles. We investigate how these peculiarities manifest in electron-hole pairing and properties of indirect magnetoexcitons in two spatially separated, independently gated graphene layers. For electron-hole pairing, we derive asymptotical expressions for the gap in energy spectrum and discuss system behavior at various controlling parameters. We derive dispersion relations for magnetoexcitons and their effective-mass decompositions, and also discuss a possibility of magnetoexcitonic super-fluidity. The systems under consideration can reveal coherent properties, dissipationless currents and Josephson phenomena at room temperature.
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| 22. |
- Misheva, M., et al.
(författare)
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Positron annihilation study of HVPE grown thick GaN layers
- 2005
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:5, s. 713-717
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Tidskriftsartikel (refereegranskat)abstract
- Single-crystalline GaN layers with a thickness up to 330 µm were grown by hydride vapor phase epitaxy on basal plane sapphire at gallium stable conditions in a bottom-fed vertical reactor at atmospheric pressure. Positron annihilation spectroscopy experiments were implemented in order to identify native point defects in the as-grown non-intentionally doped n-type GaN. Comparatively low concentrations of Ga vacancy related defects in the order of 1016 to 1017 cm–3 were extracted from the positron annihilation spectroscopy data. The Ga vacancy defect concentration was related to the intensity of the yellow photoluminescence band centered at 2.2 eV. The influence of the growth rate on the Ga vacancy related defect concentration was investigated. A trend of decreasing of the defect concentration with increasing of layer thickness is observed, which correlates with improving crystalline quality with the thickness.
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| 23. |
- Monemar, Bo, et al.
(författare)
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Effect of an (Al,In)N insertion layer on the radiative emission properties of (In,Ga)N/GaN multiple quantum well structures
- 2007
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 204:1, s. 304-308
-
Tidskriftsartikel (refereegranskat)abstract
- As an effort to investigate new techniques to reduce the effect of the strong internal polarization fields in (In,Ga)N/GaN quantum well (QW) structures we have studied the influence of inserting a thin wide band-gap AI(0 95)In(0.05)N interlayer inside the QWs, in order to modify the potential and increase the electron-hole overlap. A strong reduction of the decay times of the photoluminescence (PL) was observed in this case at all temperatures up to 300 K, without a strong reduction in PL intensity. The tunneling electron-hole transition across the interlayer is observed to be dominant at room temperature for high excitation conditions. (c) 2007 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.
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| 24. |
- Ochalski, TJ, et al.
(författare)
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Optical study of AlGaN/GaN based HEMT structures grown on sapphire and SiC
- 2005
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:7, s. 1300-1307
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Tidskriftsartikel (refereegranskat)abstract
- A detailed photoluminescence (PL), time-resolved photoluminescence (TRPL), and photoreflectance (PR) analysis of AlGaN/GaN heterostructures grown on different substrates: sapphire and silicon carbide (SiC) is presented in this paper. The properties of high electron mobility transistors (HEMTs) based on AlGaN/GaN structures are strongly dependent on the quality of the AlxGa1-xN top layer. We have examined a number of samples, grown on sapphire, in which the thicknesses of the Al0.3Ga0.7N layers vary from 18 to 75 nm. Room temperature PL under pulsed 266 nm excitation allowed for determination of the AI content in the examined thin AlGaN layers. Time-resolved PL measured at 1.6 K showed huge difference in the emission dynamics for different Al0.3Ga0.7N layer thicknesses. We observed an enormous increase of the emission decay time above the critical thickness of the AlGaN layer. PR spectra (associated with the GaN main layer) measured on AlGaN/GaN systems are discussed in terms of the thickness of the capping layer. The PR modulated by a high power 266 nm pulsed laser measured on a transistor structure exhibited an additional feature placed between signals related to the GaN and AlGaN layers, respectively. Such a transition is possible to monitor only for the structures of the best quality and is accordingly observable only on samples grown on SiC. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 25. |
- Porro, Samuele, et al.
(författare)
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Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
- 2005
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Ingår i: Physica Status Solidi (a) applications and materials science. - : John Wiley & Sons. - 1862-6300 .- 1862-6319. ; 202:13, s. 2508-2514
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Tidskriftsartikel (refereegranskat)abstract
- This work has been focused on characterization of thick 4H-SiC layers produced by sublimation epitaxy. Nickel Schottky contacts have been fabricated in order to characterize the grown material and evaluate the interfacial layer between metal and semiconductor. The characterization study includes current-voltage and capacitance-voltage high temperature measurements, from which Schottky barrier, net donor concentration and on-state resistance values have been extracted. The diodes show a typical behavior of J-V and C-V curves with temperature, with Schottky barrier heights of 1.3 eV ÷ 1.4 eV and net donor concentration of 4 × 1015 cm-3 ÷ 1 × 1016 cm-3. From the Bardeen's model on reverse J-V, the density of states of the interfacial layer has been estimated to 7 × 1011 eV-1 cm-2 ÷ 8 × 1011 eV-1 cm-2, a value that is similar to the density of states of oxide layers in deliberated MOS structures realized on the same epilayers.
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| 26. |
- Radnóczi, G. Z., et al.
(författare)
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Growth of highly curved Al1-xinxN nanocrystals
- 2005
-
Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:7
-
Tidskriftsartikel (refereegranskat)abstract
- A materials structure is reported that is characterized by high lattice curvature assigned to a compositional gradient. The phenomenon occurs for physical vapour deposition of Al1-xInxN epitaxial thin films with directional fluxes of Al and In at kinetically limited growth conditions. According to our growth model unit cells are incorporated on the growth surfaces of emerging whiskers (nanowires) with a continuously varying lattice parameter depending on their position with respect to Al- and In-rich sides of the whisker. Such curved crystals are effectively quenched solid solutions. We present a description of this generic, self-assembled curved crystal structure and its implications. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 27. |
- Roder, C., et al.
(författare)
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Strain in a-plane GaN layers grown on r-plane sapphire substrates
- 2006
-
Ingår i: Physica Status Solidi (A) Applications and Materials. - : Wiley. - 1862-6300. ; 203:7, s. 1672-1675
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Tidskriftsartikel (refereegranskat)abstract
- The strain in a-plane GaN layers of different thickness grown on r-plane sapphire substrates by hydride vapor phase epitaxy was studied by X-ray diffraction. The layers are found to be under compression in the growth plane and under tension in the growth direction. Therefore, the symmetry of the GaN unit cell is no longer hexagonal but orthorhombic. With increasing layer thickness the strain relaxes and the curvature of the wafer increases. Wafer bending is proposed to be the major strain relaxation mechanism. The anisotropic in-plane strain relaxation is attributed to the elastic and thermal anisotropy of GaN and sapphire. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
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| 28. |
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| 29. |
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| 30. |
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| 31. |
- Sanyal, Biplab, et al.
(författare)
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Ab-initio modeling of spintronic materials
- 2007
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Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 204:1, s. 33-43
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Tidskriftsartikel (refereegranskat)abstract
- Half-metallic ferromagnets with high Curie temperatures are important ingredients for spintronics applications. These include diluted magnetic semiconductors and other ordered ferromagnetic compounds. In this paper, we present ab-initio density functional electronic structure calculations of several spintronic materials addressing issues on the nature of exchange interactions, electron correlation effects, influence of defects, effects of disorder and volume dependence of exchange interactions. The calculations are done by two different methods, (i) plane wave projector augmented wave and (ii) Green function based Korringa-Kohn- Rostoker-Coherent Potential Approximation (KKR-CPA). We also present calculations of Curie temperatures using Monte-Carlo simulations with effective Heisenberg Hamiltonian within the framework of ab-initio methods.
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| 32. |
- Shubina, Tatiana, 1950-, et al.
(författare)
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Optical properties of InN related to surface plasmons
- 2005
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:14, s. 2633-2641
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Tidskriftsartikel (refereegranskat)abstract
- We report on the complex nature of infrared luminescence and absorption in InN films, which cannot be entirely explained by the concept of a conventional narrow-gap semiconductor. In particular, it concerns the detection of peaks near absorption edges by both thermally detected optical absorption and photoluminescence excitation spectroscopy and the observation of extraordinarily strong resonant enhancement of emission. To describe the experimental data a model is proposed, which takes into account surface plasmons in metal-like inclusions, modifying the optical properties of InN. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA,.
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| 33. |
- Shubina, Tatiana, et al.
(författare)
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Optical properties of InN with stoichoimetry violation and indium clustering
- 2005
-
Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:3, s. 377-382
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that nonstoichiometry is one of the main reason of strong deviation of the InN optical gap in the 0.7-2 eV range, with N/In < 1 and N/In > 1 corresponding to the lower and higher energies, respectively. The phenomenon is discussed in terms of atomic orbital energies, which are strongly different for indium and nitrogen, therefore both excess atom incorporation and elimination could change the optical gap. We estimate such trends using the approximation of the empirical nearest-neighbor tight binding theory. It is also demonstrated that resonant absorption in In-enriched regions is an additional factor lowering an effective absorption edge.
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| 34. |
- Souza Dantas, Nilton, et al.
(författare)
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Optical characterization of rock salt Pb1-xSnx Te alloys
- 2008
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Ingår i: Physica status solidi. A, Applied research. - Weinheim, Germany : Wiley. - 0031-8965 .- 1521-396X. ; 205:4, s. 837-840
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Tidskriftsartikel (refereegranskat)abstract
- The optical properties in terms of dielectric function ϵ (ħω) = ϵ1(ħω) + iϵ2(ħω) of rocksalt Pb1–xSnx Te alloys (0 ≤ x ≤ 1) are investigated experimentally by spectroscopic ellipsometry and theoretically by first-principles electronic band structure calculation. We find a strong optical response in the 0.5–2.0 eV region arising from optical absorption around the LW-line of the Brillouin zone. The response peak of the imaginary part of the dielectric functions at E = 1.6–1.8 eV shifts towards lower energies for high Sn compositions as a consequence of narrower W-point band-gap Eg(W) for the Sn-rich alloys.
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| 35. |
- Sque, S.J., et al.
(författare)
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Theoretical study on the adsorption of armchair carbon nanotubes on the hydrogenated surface of diamond
- 2006
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 203:12, s. 3107-3113
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Tidskriftsartikel (refereegranskat)abstract
- First-principles density-functional theory has been used to investigate the interaction of (metallic) (7,7) carbon nanotubes with the hydrogenated (001) surface of diamond. There is no evidence for a significant chemical interaction between the nanotubes and the diamond surface, although an appreciable binding energy is obtained. The corresponding electronic band structures are indicative of moderate electron transfer from the diamond substrate to the nanotube, which would in practice leave behind a mobile layer of holes. These results suggest that carbon nanotubes may, like buckminsterfullerene, act as suitable p-type transfer dopants for diamond.
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| 36. |
- Toropov, AA, et al.
(författare)
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Temperature-dependent polarized luminescence of exciton polaritons in a ZnO film
- 2005
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:3, s. 392-395
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Tidskriftsartikel (refereegranskat)abstract
- We report on the studies of linearly polarized photoluminescence (PL) in a (0001) oriented ZnO epitaxial film, grown by metal organic chemical vapor deposition on a GaN template. The emission of mixed longitudinal-transverse exciton polariton modes was observed up to 130 K that evidences polaritonic nature of the excitonic spectrum up to this elevated temperature.
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| 37. |
- Wiklund, Henrik, 1981-, et al.
(författare)
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A FEM-based application for numerical calculations of ellipsometric data
- 2008
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Ingår i: Physica Status Solidi (a) applications and materials science. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 205:4, s. 945-948
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Tidskriftsartikel (refereegranskat)abstract
- For modeling of advanced optical structures there is a need for stronger and more flexible modeling tools. Our aim is to develop and verify an application tool for calculations based on the Finite Element Method (FEM) of optical structures. To be able to understand which effects in the results that arises from limitations in the model, we begin by verifying the application tool for the most basic surface structures and gradually increase the complexity of the structures.
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| 38. |
- Willander, Magnus, 1948-, et al.
(författare)
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Light emission from different zinc oxide junctions and nanostructures
- 2009
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 206:5, s. 853-859
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Tidskriftsartikel (refereegranskat)abstract
- We will discuss our experimental results for optical spectra produced by hole-injection from different p-type organic and inorganic materials into n-type ZnO nanowires. The influence of different growth techniques and conditions on the nanowires and their emission spectral characteristics will then be analyzed and discussed. The latest findings on the mixture of the green emission band responsible for visible light emission from ZnO and the blue light emission from the organic polymer will be presented. Different high brightness light emitting diodes (HB-LEDs) from our grown ZnO nanowires are demonstrated. The p-type multi layer organic structures contain PEDOT:PSS as hole injectors combined with a hole transporting layer, and in some structures, a final top electron blocking/hole barrier stepping layer is placed. The purpose of this layer is to adjust the hole and electron emission from the corresponding junction side to optimize the LED performance. Structural scanning electron microscopy (SEM), electrical (I –V characteristics), photoluminescence (PL) and electroluminescence (EL) characteristics of these devices are displayed. Theoretically, we study the superfluidity of a two-dimensional system of excitonic polaritons in an optical microcavity with an embedded quantum well. Using the effective low-energy action for thermodynamic phase fluctuations, we obtain an expression for the analogue of the superfluid density in the system in terms of the “current–current” correlation function. The Kosterlits–Thouless transition temperature to the superfluid state as a function of the controlling parameters is calculated. Two methods are considered for producing traps for a polariton system in an optical microcavity. The behaviour of a two-component Bose condensate of photons and excitons is analyzed theoretically for both types of the trap. The Bose condensate is described by the coupled system of equations of the Gross–Pitaevskii type. The approximate wave functions and the spatial profiles of coupled photon and exciton condensates are obtained.
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| 39. |
- Wosinski, T., et al.
(författare)
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Domain-wall contribution to magnetoresistance of a ferromagnetic (Ga,Mn)As layer
- 2007
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Ingår i: Physica Status Solidi. A, Applied Research. - : Wiley. - 0031-8965. ; 204:2, s. 472-476
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature charge-carrier transport in simple magnetoresistive nanodevices, consisted of narrow constrictions of submicron width in the epitaxial layer of a ferromagnetic (Ga,Mn)As semiconductor, has been investigated and correlated with magnetic properties of the layer. The devices containing constrictions; revealed abrupt jumps of a reduced resistance that appeared when the sweeping magnetic field crossed the regions of the coercive field of the layer magnetization. In contrast, the non-constricted reference device displayed abrupt jumps of an enhanced resistance at the same values of magnetic field. We interpret the both features, whose positions on the magnetic-field scale reflect the hysteresis loop of magnetization, as manifestation of domain wall contribution to the (Ga,Mn)As layer resistance. The negative contribution of a domain wall to the resistance in the constricted device results most likely from the suppression of the weak localization effects by a domain wall located at the constriction.
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| 40. |
- Wronkowska, A.A., et al.
(författare)
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Lattice absorption of Be-containing semiconductor alloys determined by spectroscopic ellipsometry
- 2008
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Ingår i: Physica Status Solidi (a) applications and materials science. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 205:4, s. 849-853
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Tidskriftsartikel (refereegranskat)abstract
- Lattice absorption of Zn1–x –yBex Mgy Se and Cd1–x –yBex Zny Se mixed crystals grown by a high pressure Bridgman method has been investigated by infrared spectroscopic ellipsometry in the wave number range from 230 cm–1 to 5000 cm–1. Ellipsometric spectra of Cd1–x –yBex Zny Se crystals display features in the spectral range 350–550 cm–1 associated with BeSe-type phonon modes. In the optical spectra of Zn1–x –yBex Mgy Se crystals both BeSe-type and MgSe-type lattice absorption bands are detected. The MgSe-like modes are located at approximately 300 cm–1. The frequencies and oscillator strengths of optical phonon modes depend strongly on the alloy composition
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| 41. |
- Wronkowska, A.A., et al.
(författare)
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Spectroscopic ellipsometry and photoluminescence investigation of Zn1-x-yBexMgySe and Cd1-x-yBexZnySe Crystals
- 2008
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 205:4, s. 854-858
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Tidskriftsartikel (refereegranskat)abstract
- Optical and luminescence properties of the Bridgman-grown Cd1–x –yBex Zny Se and Zn1–x –yBex Mgy Se crystals are reported. Spectroscopic ellipsometry was employed for determination of spectral dependence of the complex dielectric function (E) in the photon energy range 0.75–6.5 eV. Below the absorption edge the refractive indices n (E) of the alloys were modelled using a Sellmeier-type relation. The excitonic band-gap energies were estimated from the ellipsometric and photoluminescence measurements. Compositional effects in the ellipsometric and photoluminescence spectra are discussed.
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| 42. |
- Buyanova, Irina A., et al.
(författare)
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Magneto-optical spectroscopy of spin injection and spin relaxation in ZnMnSe/ZnCdSe and GaMnN/InGaN spin light-emitting structures
- 2007
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Ingår i: 2006 E-MRS Fall Meeting. - : Wiley. ; , s. 159-173
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Konferensbidrag (refereegranskat)abstract
- In this paper we review our recent results from in-depth investigations of physical mechanisms which govern efficiency of several processes important for future spintronic devises, such as spin alignment within diluted magnetic semiconductors (DMS), spin injection from DMS to non-magnetic spin detectors (SDs) and also spin depolarization within SD. Spin-injection structures based on II-VIs (e.g. ZnMnSe/Zn(Cd)Se) and III-Vs (e.g. GaMnN/Ga(In)N) were studied as model cases. Exciton spin relaxation within ZnMnSe DMS, important for spin alignment, was found to critically depend on Zeeman splitting of the exciton states and is largely facilitated by involvement of longitudinal optical (LO) phonons. Optical spin injection in ZnMnSe/Zn(Cd)Se was shown to be governed by (i) commonly believed tunneling of individual carriers or excitons and (ii) energy transfer via localized excitons and spatially separated localized electron-hole pairs (LEHP) located within DMS. Unexpectedly, the latter mechanism is in fact found to dominate spin injections. We shall also show that spin depolarization in the studied structures is essentially determined by efficient spin relaxation within non-magnetic spin detectors, which is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed.
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| 43. |
- Fokine, Michael
(författare)
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Manipulating glass for photonics
- 2009
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Ingår i: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE. - : Wiley. - 1862-6300. ; 206:5, s. 880-884
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Tidskriftsartikel (refereegranskat)abstract
- A generalized concept for local manipulation of three-dimensional glass materials is described. The basic principle is to use means to deposit energy into the material to enable localized and selective changes in the bond structure of the glass matrix, causing a localized modification of the thermal equilibrium properties of the material. The different regions of the glass will then behave differently when the sample is subsequently heated homogeneously. If the difference in the thermal dynamics between modified and un-modified regions is significant, thermal treatment of the material can result in a self-organizing structure. The aim here is to provide a generalized concept of differential systems and self-organizing structures, using chemical composition Bragg gratings as an example. In this case, differential diffusion results in self-organizing structures consisting of a variation of the chemical composition, with compositional features smaller than 250 nm.
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| 44. |
- Mlyuka, Nuru, et al.
(författare)
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Thermochromic VO2-Based Multilayer Films with Enhanced Transmittance and Solar Modulation
- 2009
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Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 206:9, s. 2155-2160
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Tidskriftsartikel (refereegranskat)abstract
- Vanadium dioxide (VO2) shows an abrupt and reversible change in optical and electrical properties when the temperature is raised beyond a critical point of similar to 68 degrees C. Films made from this material have a potential to be used in energy efficient "smart" windows with temperature-dependent throughput of solar radiation. Two of the drawbacks of this material have been its low luminous transmittance and limited solar modulation of transmittance during switching. In this work we report calculations and experiments on multilayers Of VO2 and TiO2, produced by reactive DC magnetron sputtering, that significantly improve the luminous transmittance and solar modulation of the films during switching. We also explore the angular-dependent transmittance of five-layer TiO2/VO2/TiO2/VO2/TiO2 films and demonstrate that the modulation of luminous and solar transmittance can be enhanced at non-normal angles of incidence.
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| 45. |
- Pikulev, V. B., et al.
(författare)
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Singlet oxygen inhibits nonradiative defects in porous silicon
- 2009
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Ingår i: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE. - : Wiley. - 1862-6300. ; 206:6, s. 1268-1272
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Tidskriftsartikel (refereegranskat)abstract
- Experimental evidences are presented for the first time that singlet oxygen generated ex situ acts as an inhibitor of nonradiative recombination in porous silicon (PSi). This effect is observed on a pristine PSi as well as on degraded porous layers quenched by ozone adsorption. A photoluminescence (PL) enhancement produced by singlet oxygen is accompanied with only slight oxidation of a PSi. We assume that the observed effect on PL efficiency is due to gentle selective oxidation of single defects on silicon nanocrystal surface.
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