| 1. |
- Afrasiabi, Roodabeh, et al.
(författare)
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Microwave mediated synthesis of semiconductor quantum dots
- 2012
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 9:7, s. 1551-1556
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal quantum dots (QD) have tuneable optoelectronic properties and can be easily handled by simple solution processing techniques, making them very attractive for a wide range of applications. Over the past decade synthesis of morphology controlled high quality (crystalline, monodisperse) colloidal QDs by thermal decomposition of organometallic precursors has matured and is well studied. Recently, synthesis of colloidal QDs by microwave irradiation as heating source is being studied due to the inherently different mechanisms of heat transfer, when compared to solvent convection based heating. Under microwave irradiation, polar precursor molecules directly absorb the microwave energy and heat up more efficiently. Here we report synthesis of colloidal II-VI semiconductor QDs (CdS, CdSe, CdTe) by microwave irradiation and compare it with conventional synthesis based on convection heating. Our findings show that QD synthesis by microwave heating is more efficient and the chalcogenide precursor strongly absorbs the microwave radiation shortening the reaction time and giving a high reaction yield.
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| 2. |
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| 3. |
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| 4. |
- Berlind, Torun, 1965-, et al.
(författare)
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Effects of ion concentration on refractive indices offluids measured by the minimum deviation technique
- 2008
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - Weinheim : WILEY-VCH Verlag GmbH & Co. KGaA. - 1610-1634 .- 1610-1642. ; 5:5, s. 1249-1252
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Tidskriftsartikel (refereegranskat)abstract
- The prism minimum deviation technique has been used to measure the fluid dependence of refractive indices. Fluids with varying ion concentration (0 to 1.0 M) and varying protein concentration (0.01-10 mg/ml) have been examined and the measurements show that these parameters influence the refractive index values. Also it is shown by simulations that it is important to take the change of refractive index of the fluid into account when evaluating insitu protein adsorption measurements.
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| 5. |
- Bi, Zhaoxia, et al.
(författare)
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InN quantum dots on GaN nanowires grown by MOVPE
- 2014
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Ingår i: physica status solidi (c). - : Wiley. - 1862-6351 .- 1610-1642 .- 1610-1634. ; 11, s. 421-424
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Tidskriftsartikel (refereegranskat)abstract
- In this work, growth of InN quantum dots (QDs) on GaN nanowires (NWs) by metal-organic vapour phase epitaxy is demonstrated, illustrating the feasibility to combine 0D and 1D structures for nitride semiconductors. Selective area growth was used to generate arrays of c-oriented GaN NWs using Si3N4 as the mask material. In general, InN QDs tend to form at the NW edges between the m-plane side facets, but the QD growth can also be tuned to the side facets by controlling the growth temperature and the growth rate. TEM characterization reveals that I1-type stacking faults are formed in the QDs and originate from the misfit dislocations at the InN/GaN interface. Photoluminescence measurement at 4 K shows that the peak shifts to high energy with reduced dot size. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 6. |
- Chulapakorn, Thawatchart, 1988-, et al.
(författare)
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MeV ion irradiation effects on the luminescence properties of Si-implanted SiO2-thin films
- 2016
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Ingår i: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley-VCH Verlagsgesellschaft. - 1862-6351 .- 1610-1634 .- 1610-1642. ; 13:10-12, s. 921-926
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Tidskriftsartikel (refereegranskat)abstract
- The effects of MeV heavy ion irradiation at varying fluence and flux on excess Si, introduced in SiO2 by keV ion implantation, are investigated by photoluminescence (PL). From the PL peak wavelength (λ) and decay lifetime (τ), two PL sources are distinguished: i) quasi-direct recombination of excitons of Si-nanoparticles (SiNPs), appearing after thermal annealing (λ > 720 nm, τ ∼ μs), and ii) fast-decay PL, possibly due to oxide-related defects (λ ∼ 575-690 nm, τ ∼ ns). The fast-decay PL (ii) observed before and after ion irradiation is induced by ion implantation. It is found that this fast-decay luminescence decreases for higher irradiation fluence of MeV heavy ions. After thermal annealing (forming SiNPs), the SiNP PL is reduced for samples irradiated by MeV heavy ions but found to stabilize at higher level for higher irradiation flux; the (ii) band vanishes as a result of annealing. The results are discussed in terms of the influence of electronic and nuclear stopping powers.
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| 7. |
- Dagnelund, Daniel, et al.
(författare)
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Effect of thermal annealing on defects in post-growth hydrogenated GaNP
- 2013
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : John Wiley & Sons. - 1610-1634 .- 1610-1642. ; 10:4, s. 561-563
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Tidskriftsartikel (refereegranskat)abstract
- Effect of thermal annealing on paramagnetic centers in post-growth hydrogenated GaN0.0081P0.9919 epilayer is examined by means of photoluminescence and optically detected magnetic resonance (ODMR) techniques. In recent studies, several Ga-interstitial (Gai) related centers were found to be activated by the presence of hydrogen in the hydrogenated GaNP alloys. These centers compete with near-band edge radiative recombination. Annealing at 400 ºC in Ar-ambient is found to cause quenching of the Gai-related ODMR signals that were activated by post-growth hydrogenation. We tentatively ascribe this effect to dissociation of the H-Gai complexes and subsequent out-diffusion of H.
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| 8. |
- Darakchieva, V., et al.
(författare)
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Phonons in strained AlGaN/GaN superlattices
- 2007
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 4:1, s. 170-174
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Tidskriftsartikel (refereegranskat)abstract
- Phonons in strained AlGaN/GaN superlattices (SLs) with constant periods but different Al composition have been studied using a combination of infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The following SL modes were identified: i) AlGaN localized E1(TO) modes identified for the first time and AlGaN localized A1 (LO) phonons; ii) GaN localized E2, E1(TO) and A1(LO) phonons; iii) delocalized E1(LO) phonons; iv) A1(TO) phonon; v) two modes around 660 cm-1 and 594-625 cm-1, respectively, not predicted by theory. The effects of strain and composition on the phonon frequencies were established and discussed.
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| 9. |
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| 10. |
- Eberlein, T.A.G., et al.
(författare)
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Movement and pinning of dislocations in SiC
- 2007
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 4:8, s. 2923-2928
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Tidskriftsartikel (refereegranskat)abstract
- SiC bipolar devices show a degradation under forward-biased operation due to the formation and rapid propagation of stacking faults in the active region of the device. It is believed that the observed rapid stacking fault growth is due to a recombination-enhanced dislocation glide (REDG) mechanism at the bordering partial dislocations having either Si or C core atoms. We investigated the effect of charge on the dislocation kinks and found that only silicon kinks have a deep filled band above the valence band. Trapping of holes into this band permits dislocation glide at room temperature. This mechanism is distinct from REDG as it requires only holes to be trapped at a Si partial and not in addition electrons in stacking fault states. We furthermore looked at the pinning of dislocations by nitrogen and boron and found a strong pinning of the C core by N and of the Si core by B.
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| 11. |
- Fitting, H.-J., et al.
(författare)
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Luminescent Defect Dynamics in Amorphous SiO2:H
- 2005
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 2, s. 693-698
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Tidskriftsartikel (refereegranskat)
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| 12. |
- Fokine, Michael, 1970-, et al.
(författare)
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Spectral features of specular reflection from nanoparticle films
- 2010
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 8:9, s. 2673-2675
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Tidskriftsartikel (refereegranskat)abstract
- In this work we analyze the internal reflection (Fresnel reflection) from Au nanoparticles on the end face of optical fibers. We demonstrate that changes in the refractive index of the surrounding medium can be detected by shifts in the reflection spectra associated with changes in the Localized Surface Plasmon Resonance of the Au-Nanoparticles. The spectral response is simulated using a model based on the interference in multilayer structures and can be described by transfer-matrix method.
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| 13. |
- Gogova, D., et al.
(författare)
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HVPE GaN substrates : growth and characterization
- 2010
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 7:7-8, s. 1756-1759
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Tidskriftsartikel (refereegranskat)abstract
- GaN substrates with low dislocation densities were prepared by halide vapor-phase epitaxy (HVPE) on c-plane sapphire and by means of a post-growth laser-induced lift-off or natural stress-induced (self-) separation process. The HVPE growth on InGaN/GaN buffer layers and subsequent self-separation method was seen as advantageous, in comparison with the laser-induced lift-off one, in terms of lower cost and better crystalline quality of the GaN material obtained. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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| 14. |
- Grini, Sigbjörn, et al.
(författare)
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Secondary ion mass spectrometry as a tool to study selenium gradient in Cu2ZnSn(S,Se)4
- 2017
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; :6
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Tidskriftsartikel (refereegranskat)abstract
- Secondary ion mass spectrometry (SIMS) has been utilized to study compositional gradients in compound-sputtered and annealed Cu2ZnSn(S,Se)(4) (CZTSSe). SIMS image depth profiling shows a non-uniform spatial distribution of selenium and supports a mechanism where selenization is accompanied by grain growth rather than substitution of selenium for sulfur. Furthermore, SIMS depth profiles of S and Se using O-2(+) primary ions and detecting molecular ions of the MCs+ type using Cs+ primary ions have been compared, where a linear relationship between the sulfur and selenium concentration suitable for compositional analysis is observed for concentrations with an Se/(S+Se) ratio in the range from 0.25 to 0.65. 3D image of the spatial Se distribution in a 20 x 20 mu m(2) grid measured with SIMS image depth profiling.
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| 15. |
- Haarahiltunen, Antti, et al.
(författare)
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Gettering of iron in CZ-silicon by polysilicon layer
- 2011
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley-VCH Verlagsgesellschaft. - 1610-1634 .- 1610-1642. ; 8:3, s. 751-754
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Tidskriftsartikel (refereegranskat)
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| 16. |
- Hofmann, T., et al.
(författare)
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Anisotropy of the Γ-point effective mass and mobility in hexagonal InN
- 2006
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1610-1634 .- 1610-1642. ; 3:6, s. 1854-1857
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Tidskriftsartikel (refereegranskat)abstract
- We determine the anisotropic electron effective mass and mobility parameters in wurtzite InN thin films with free electron concentration Nfrom 1.8 × 1017 cm–3 to 9.5 × 1018 cm–3 using Infrared Magneto-optic Generalized Ellipsometry. The room-temperature measurements were carried out with magnetic fields up to 4.5 T. For the Γ-point we estimate m*⊥ = 0.047m0 and m*‖ = 0.039m0 for polarization perpendicular and parallel to the c -axis, respectively. Scattering by impurities or ionized donors may explain the decrease of mobility for polarization parallel to the c -axis from 1600 cm2/(Vs) to 800 cm2/(Vs) with increase in N , where the perpendicular mobility is further decreased, likely caused by additional grain boundary scattering.
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| 17. |
- Holmberg, Patrik, 1971-, et al.
(författare)
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Study of incubation effects during surface ablation using picosecond pulses at a wavelength of 800 nm
- 2011
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - Weinheim : WILEY-VCH Verlag GmbH & Co. - 1610-1634 .- 1610-1642. ; 8:9, s. 2862-2865
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Tidskriftsartikel (refereegranskat)abstract
- A comparison of laser ablation on the front-surface (surface facing the laser) and back-surface of 1.1 mm thick boro-aluminosilicate glass plates has been performed using 1 ps pulses at a wavelength of 800 nm. The resulting structures of front- and back-surface ablation are compared relative to an input design geometry of 40 µm deep and 40 µm wide surface channels. The influence of incubation effects on the final structure is discussed.
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| 18. |
- Hounsome, L.S., et al.
(författare)
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Role of extended defects in brown colouration of diamond
- 2007
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 4:8, s. 2950-2957
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Tidskriftsartikel (refereegranskat)abstract
- The absorption spectrum of brown diamond is broad and featureless, in both natural type IIa and CVD-grown material. It is argued that such an absorption is due to an extended, rather than a point, defect. Ab-initio modelling studies have been conducted on dislocations and extended vacancy-related defects. While certain dislocations could potentially explain the origin of colour, their density is too low to account for experimentally observed absorption magnitudes. It is demonstrated that a vacancy disk lying in the {111} plane has an absorption spectrum similar to that seen in natural and CVD brown diamond. Such disks are unstable above about 200 vacancies and should relax to dislocation loops in natural diamond. Hydrogen is shown to passivate the optical activity of the disks.
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| 19. |
- Jalalian, Abolfazl, et al.
(författare)
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Fabrication of Ca, Zr doped BaTiO 3 ferroelectric nanofibers by electrospinning
- 2012
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 9:7, s. 1574-1576
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Tidskriftsartikel (refereegranskat)abstract
- As first time, (Ba0.85Ca0.15)(Ti0.9Zr0.1)O-3 (BCTZ) nanofibers are synthesized by sol-gel assisted electrospining technique. Non-woven and bead-free BCTZ nanofibers mat was formed and a single chemical phase was achieved after calcination of the nanofibers at 700 degrees C in air. XRD and Raman spectroscopy show that BCTZ nanofibers crystallized in the morphotropic phase boundary (MPB) region.
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| 20. |
- Johansson, Sofia, et al.
(författare)
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High frequency vertical InAs nanowire MOSFETs integrated on Si substrates
- 2012
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Ingår i: Physica Status Solidi. C, Current Topics in Solid State Physics. - : Wiley. - 1610-1634. ; 9:2, s. 350-353
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Tidskriftsartikel (refereegranskat)abstract
- RF and DC characterization of vertical InAs nanowire MOSFET on Si substrates are presented. Nanowire arrays are epitaxially integrated on Si substrates by use of a thin InAs buffer layer. For device fabrication, high-k HfO2 gate dielectric and wrap-gates are used. Post-deposition annealing of the high-k is evaluated by comparing one annealed and one not-annealed sample. The annealed sample show better DC characteristics in terms of transconductance, g(m) = 155 mS/mm, and on-current, I-on = 550 mA/mm. Box plots of on-current, on-resistance and transconductance for all 190-nanowire-array transistors on the annealed sample suggest that the electrical properties of the nanowires are preserved when scaling the nanowire diameter. Finally, high frequency characterisation yields a unity current gain cut-off frequency of f(t) = 9.3 GHz for the annealed sample and f(t) = 2.0 GHz for the not-annealed sample. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 21. |
- Junesand, Carl, et al.
(författare)
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Surface morphology of indium phosphide grown on silicon by nano-epitaxial lateral overgrowth
- 2009
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 6:12, s. 2785-2788
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Tidskriftsartikel (refereegranskat)abstract
- InP is grown on Si by nano-epitaxial lateral overgrowth (NELOG or nano-ELOG) on patterns consisting of net-type openings under different growth conditions. Surface morphology is characterized with AFM and profilometer and optical quality assessed by Micro Photoluminescence measurements (mu-PL). Results show that growth conditions affect both morphology and optical quality, with thicker layers generally corresponding to better surface morphology. Lower growth temperature seems to improve surface morphology irrespective of thickness, and ELOG layers exhibit significantly better morphology than the planar layer.
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| 22. |
- Karim, Amir, et al.
(författare)
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Characterization of InAs/GaSb type€II superlattice photodiodes for mid€wave IR with different mesa sidewall passivation schemes
- 2012
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; c9:7, s. 1690-2
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Tidskriftsartikel (refereegranskat)abstract
- We report on the electrical material characterization of InAs/GaSb type-II superlattice (T2SL) mid-wave infrared (MWIR) photodiodes with different passivation schemes on the mesa-sidewalls with significant differences in the resulting low temperature dark currents. Devices fabricated by dry etching passivated with polymerized photoresist, show orders of magnitude lower dark currents as compared to unpassivated devices. The mesa side walls were examined using high resolution transmission electron microscopy (HRTEM) with a special focus on the interface between the superlattice material the dielectric passivation. Material analysis on nanometer scale at the mesa sidewall interface was performed using energy dispersive X-ray (EDX) spectrometry. EDX line scans were obtained from interfaces for different passivated unpassivated devices, using the highly focused electron beam in TEM, to investigate the chemical compositions. The unpassivated photoresist-passivated mesas, with different electrical properties, revealed different sidewall morphologies compositions. An oxygen containing layer was observed in photoresist-passivated devices covering the whole mesa sidewall. We think this plays a role in reducing surface leakage dark current. In HR-TEM the mesa sidewall topography reveals preferential etching of one superlattice component as previously observed. Nevertheless, the dielectric material covers the sidewall uniformly.
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| 23. |
- Kasic, A., et al.
(författare)
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Phonons and free-carrier properties of binary, ternary, and quaternary group-III nitride layers measured by infrared Spectroscopic Ellipsometry
- 2003
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 0:6 SPEC. ISS., s. 1750-1769
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work reviews recent ellipsometric investigations of the infrared dielectric functions of binary, ternary, and quaternary group-III nitride films. Spectroscopic Ellipsometry in the mid-infrared range is employed for the first time to determine phonon and free-carrier properties of individual group-III nitride heterostructure components, including layers of some ten nanometer thickness. Assuming the effective carrier mass, the free-carrier concentration and mobility parameters can be quantified upon model analysis of the infrared dielectric function. In combination with Hall-effect measurements, the effective carrier masses for wurtzite n- and p-type GaN and n-type InN are obtained. The mode behavior of both the E1(TO) and A1(LO) phonons are determined for ternary compounds. For strain-sensitive phonon modes, the composition and strain dependences of the phonon frequencies are differentiated and quantified. Information on the crystal quality and compositional homogeneity of the films can be extracted from the phonon mode broadening parameters. A comprehensive IR dielectric function database of group-III nitride materials has been established and can be used for the analysis of complex thin-film heterostructures designed for optoelectronic device applications. Information on concentration and mobility of free carriers, thickness, alloy composition, average strain state, and crystal quality of individual sample constituents can be derived. © 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 24. |
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| 25. |
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| 26. |
- Kundozerova, T. V., et al.
(författare)
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Binary anodic oxides for memristor-type nonvolatile memory
- 2012
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 9:7, s. 1699-1701
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of the optical properties of InGaAs/GaAs double quantum wells (QWs) grown by molecular beam epitaxy (MBE) on (100) and (311)A GaAs substrates has been studied by photoluminescence (PL). It is found that for an excitation of 50 mW, the PL quenching for (100) and (311)A QWs occurs at 220 K and 300 K, respectively. This suggests that the high index plane (311)A has superior structural properties and less non-radiative defect centers than the conventional (100) plane. The better optical quality of the QWs grown on (311)A is also confirmed by the narrowing of the full width at half-maximum (FWHM) of the PL emission: 10 nm for (311)A and 20 nm for (100). From these findings it is expected that optical devices grown on (311)A GaAs planes should have better performances than those grown on conventional (100) orientation. We have also carried out a systematic study to investigate the effect of post-growth thermal annealing on the optical quality of the QWs. We observed a substantial improvement of the PL efficiency with annealing temperatures in the range 500-700 °C for all samples. However, this PL enhancement is accompanied by a blueshift. These energy shifts can be explained by interdiffusion or intermixing of In and Ga atoms at the interfaces between the QWs and the barriers. A noticeable narrowing of the PL linewidth with higher annealing temperatures could be explained by a homogenisation of the quantum well interfaces.
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| 27. |
- Larsson, Henrik, et al.
(författare)
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Free-standing HVPE-GaN Layers
- 2003
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 0:7, s. 1985-1988
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Tidskriftsartikel (refereegranskat)abstract
- We have grown GaN layers with a thickness up to 340 μm in an rf-heated vertical HVPE reactor with a bottom-fed design. The GaN layers were separated from the sapphire substrate by a LLO process. The free-standing GaN was investigated by HRXRD, AFM and low temperature CL. The FWHM values of the ω-scans are 96 and 129 arcsec for the (104) and (002) reflection, respectively, which indicates high crystalline quality. The c and a lattice parameters are determined as c = 0.51850 ± 0.00004 nm and a = 0.31890 ± 0.00004 nm, indicating stress free material. The etch pit density was estimated to be 1 × 107 cm−2. The used HVPE growth procedure together with the subsequent LLO are obviously capable to provide high-quality free-standing GaN material for further epitaxial overgrowth.
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| 28. |
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| 29. |
- Liuolia, Vytautas, et al.
(författare)
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Near- and far-field optical characterization of InGaN photonic crystal light emitting diodes
- 2012
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 9:7, s. 1664-1666
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Tidskriftsartikel (refereegranskat)abstract
- Light extraction from InGaN photonic crystal (PhC) light emitting diodes (LEDs) has been studied by scanning near-field optical microscopy and time-resolved photoluminescence. The observed patterns of the near-field intensity are complex and do not correspond to the physical structure of the photonic crystal. Comparison with conventional LEDs without the PhC showed that PhC not only improves the light extraction, but also makes the LED emission more homogeneous.
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| 30. |
- Marcinkevicius, Saulius, et al.
(författare)
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Carrier dynamics and localization in AlInN/GaN heterostructures
- 2013
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 10:5, s. 853-856
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Tidskriftsartikel (refereegranskat)abstract
- Photoexcited carrier dynamics and localization potentials in Al0.86In0.14N/GaN heterostructure have been examined by time-resolved photoluminescence (PL), transient photoreflectance and scanning near-field optical spectroscopy. The large GaN and AlInN PL intensity difference, and the short AlInN PL decay and GaN PL rise times indicate efficient photoexcited carrier transfer from AlInN to GaN via sub-band edge states. Near-field PL scans and photoreflectance data show that the diameter of the localization sites and the distance between them are well below 100 nm. Majority of these states is assigned to In clusters, in which the valence band has a higher energy than the valence band in a uniform AlInN alloy. It is likely that the carrier transport through the sub-band edge states proceeds via high conductivity channels involving extended defects.
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| 31. |
- Matsui, Satoshi, et al.
(författare)
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All-optical modulation using intersubband transitions at 1.55 mu m in GaN/AlN multiple quantum well
- 2005
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 2:7, s. 2748-2752
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Tidskriftsartikel (refereegranskat)abstract
- All-optical modulation using intersubband transition (ISBT) resonant light (wavelength of 1.55 μm) and induced by UV interband transition (IBT) resonant light (325 nm or 213 nm) was demonstrated in a GaN/AlN multiple quantum well (MQW) waveguide device. The modulation was selective and occurred only for p-polarized ISBT resonant light in accordance with ISBT characteristics. An IBT relaxation time of 1.5 ns was obtained by fitting the experimental results with a three-level model, taking into consideration the valence band, the conduction band and the trap-state.
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| 32. |
- Metaferia, Wondwosen, et al.
(författare)
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Selective area heteroepitaxy through nanoimprint lithography for large area InP on Si
- 2012
-
Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 9:7, s. 1610-1613
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Tidskriftsartikel (refereegranskat)abstract
- The use of nanoimprint lithography, a low cost and time saving alternative to E-beam lithography, for growing heteroepitaxial indium phosphide layer on silicon is demonstrated. Two types of patterns on 500 nm and 200 nm thick silicon dioxide mask either on InP substrate or InP seed layer on silicon were generated by UV nanoimprint lithography: (i) circular openings of diameter 150 nm and 200 nm and (ii) line openings of width ranging from 200 nm to 500 nm. Selective area growth and epitaxial lateral overgrowth of InP were conducted on these patterns in a low pressure hydride vapour phase epitaxy reactor. The epitaxial layers obtained were characterized by atomic force microscopy, scanning electron microscopy and micro photoluminescence. The growth from the circular openings on InP substrate and InP (seed) on Si substrate is extremely selective with similar growth morphology. The final shape has an octahedral flat top pyramid type geometry. These can be used as templates for growing InP nanostructures on silicon. The grown InP layers from the line openings on InP substrates are ∌ 2.5 Όm thick with root mean square surface roughness as low as 2 nm. Completely coalesced layer of InP over an area of 1.5 mm x 1.5 mm was obtained.The room temperature photoluminescence intensity from InP layers on InP substrate is 55% of that of homoepitaxial InP layer. The decrease in PL intensity with respect to that of the homoepitaxial layer is probably due to defects associated with stacking faults caused by surface roughness of the mask surface. Thus in this study, we have demonstrated that growth of heteroepitaxial InP both homogeneously and selectively on the large area of silicon can be achieved. This opens up the feasibility of growing InP on large area silicon for several photonic applications.
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| 33. |
- Montesdeoca-Santana, Amada, et al.
(författare)
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Phosphorous gettering in acidic textured multicrystalline solar cells
- 2011
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 8:3, s. 743-746
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Tidskriftsartikel (refereegranskat)abstract
- The influence of phosphorus gettering is studied in thiswork applied to an acidic textured multicrystalline siliconsubstrate. The texturization was achieved with an HF/HNO3 solution leading to nanostructures on the silicon surface. It has been demonstrated in previous works that this textured surface decreases the reflectance on the solar cell and increases the surface area improving the photon collection and enhancing the short circuit current.The present study investigates the effect on the minoritycarrier lifetime of the phosphorous diffusion when it is carried out on this textured surface. The lifetime is measured by means microwave photoconductance decay and quasi steady state phototoconductance devices. The diffused textured wafers are used to fabricate solar cells and their electrical parameters are analyzed.
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| 34. |
- Nelander, Rikard, et al.
(författare)
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Temperature degradation of the gain transition in terahertz quantum cascade lasers - the role of acoustic phonon scattering
- 2009
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Ingår i: physica status solidi (c). - : Wiley. - 1610-1634 .- 1862-6351 .- 1610-1642. ; 6:2, s. 579-582
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Konferensbidrag (refereegranskat)abstract
- The temperature degradation in terahertz quantum cascade lasers is investigated with the focus on the role acoustic phonon scattering. A self-energy describing the electron-acoustic phonon interaction is derived and used to study the importance in transport and optical properties. We observe a strong degradation of the gain peak with temperature. Despite the very small coupling to electrons, the exclusion of acoustic phonon scattering alters the current and peak gain in the order of 5%. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 35. |
- Nisar, Jawad, 1980-, et al.
(författare)
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Study of electronic and optical properties of BiTaO4 for photocatalysis
- 2012
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley-VCH Verlagsgesellschaft. - 1610-1634 .- 1610-1642. ; 9:7, s. 1593-1596
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Tidskriftsartikel (refereegranskat)abstract
- We present the optical absorption spectrum of BiTaO4 using the photo acoustic spectroscopy (PAS) technique and first principle approach. Band gap have been estimated 2.65 and 2.45 eV using PAS method and DFT calculations, respectively. Position of reduction and oxidation level with respect to vacuum level are identified, which shows that BiTaO4 can be used as photocatalyst for hydrogen production. Electronic structure is explained by plotting total density of states (TDOS).
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| 36. |
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| 37. |
- Ochalski, T.J., et al.
(författare)
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Optical study of AlGaN/GaN based HEMT structures
- 2005
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - 1610-1634 .- 1610-1642. ; 2, s. 2791-2794
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Tidskriftsartikel (refereegranskat)
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| 38. |
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| 39. |
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| 40. |
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| 41. |
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| 42. |
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| 43. |
- Paskova, Tanja, et al.
(författare)
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Polar and nonpolar HVPE GaN substrates: impact of doping on the structural, electrical and optical characteristics
- 2009
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 6:2, s. 344-347
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Tidskriftsartikel (refereegranskat)abstract
- Polar and nonpolar bulk GaN substrates with low defect density and high structural and optical quality are demonstrated. The effect of doping by silicon, oxygen and iron within moderate doping levels on the properties of the polar GaN substrates was found uncompromised, as confirmed by high resolution X-ray diffraction and low temperature photoluminescence spectroscopy. In contrast, the lattice parameters were affected significantly, which has to be considered in the subsequent homoepitaxial device growth. The boule growth and respectively the nonpolar substrate homogeneity were found to be hampered by the doping, due to surface microcracking and higher impurity incorporation, while n-type undoped nonpolar substrates were demonstrated of superior quality.
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| 44. |
- Pereira, M. F., et al.
(författare)
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Microscopic theory for intersubband spontaneous emission
- 2007
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Ingår i: Physica Status Solidi. C, Current Topics in Solid State Physics. - : Wiley. - 1610-1634. ; 4:2, s. 356-359
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Tidskriftsartikel (refereegranskat)abstract
- The amplified spontaneous emission spectra of quantum-cascade laser structures is computed with a Keldysh Green's functions theory. We show that the emission spectra are sharpened in comparison to gain spectra due to wave guide propagation. In addition the different dependence on level occupation causes moderate differences between gain and emission peak positions. Our fit-parameter-free theory is valid in ranges of strong nonequilibrium, where fit-parameters do not even exist.
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| 45. |
- Pinos, Andrea, et al.
(författare)
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Scanning near-field optical spectroscopy of AlGaN epitaxial layers
- 2012
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 9:7, s. 1617-1620
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Tidskriftsartikel (refereegranskat)abstract
- Band gap fluctuations and carrier localization in AlxGa1-xN films with x values varying from 0.30 to 0.50 has been studied by scanning near-field optical microscopy (SNOM) by measuring photoluminescence. The measurements have revealed a dual localization potential. Microscopic scale potential variations, detected by the SNOM, were most pronounced in the lower Al content samples. The nanoscopic carrier localization potentials, evaluated from the width of the photoluminescence spectra, were largest in layers with the largest AlN molar fraction. The large scale potential fluctuations were attributed to Ga rich regions close to grain boundaries or atomic layer steps. The density, size and band gap energy of these domains were found to be composition dependent. The nanoscopic potential variations have been assigned to small-scale compositional fluctuations, possibly, occurring due to formation of Al rich grains during growth.
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| 46. |
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| 47. |
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| 48. |
- Santos, P., et al.
(författare)
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Electrical activity of multivacancy defects in silicon
- 2012
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 9:10-11, s. 2000-2004
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Tidskriftsartikel (refereegranskat)abstract
- The formation processes and properties of multivacancy defects in Si have been recently the subject of several re-search studies. Here we report on density functional calculations concerning the stability and electrical activity of the tetravacancy, pentavacancy and hexavacancy complexes in Si. Formation energy calculations indicate that Four-Fold Coordinated (FFC) V4 and V5 are more stable than Part-of-Hexagonal-Ring (PHR) or planar structures by at least 1.2 eV and 0.6 eV, respectively. This relative stability order between configurations remains unchanged for different charged states from double plus to double minus. Calculations of the electrical activity predict deep acceptor levels for the FFC defects. Accordingly, electron traps related to (–/0) and (=/–) levels near Ec – 0.5 eV were found for V4 and V5, whereas levels for V6 were estimated at Ec – 0.35 eV. No donor levels were found for these defects
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| 49. |
- Savini, G., et al.
(författare)
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Structure and energy of partial dislocations in wurtzite-GaN
- 2007
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 4:8, s. 2945-1949
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Tidskriftsartikel (refereegranskat)abstract
- First-principle calculations have shown that both the partials can be electrically active. In particular we have shown the Ga(g) core partials are a good candidate for the observed absorption peak at 2.4 eV revealed by energy loss spectroscopy measurements. The symmetric and asymmetric reconstructions have relatively close formation energies. Our results have suggested that the asymmetric reconstructions, characterized by strong bonds along the dislocation line are favourable in intrinsic materials. However, in strongly p and n-type materials or in high stress field the symmetric reconstructions can become energetically more stable. These reconstructions are always electrically active with a deep band across the forbidden gap.
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| 50. |
- Scott, K., et al.
(författare)
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Non-stoichiometry and non-homogeneity in InN
- 2005
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - 1610-1634 .- 1610-1642. ; 2, s. 2263-2266
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Tidskriftsartikel (refereegranskat)
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