| 1. |
- Roder, C., et al.
(author)
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Strain in a-plane GaN layers grown on r-plane sapphire substrates
- 2006
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In: Physica Status Solidi (A) Applications and Materials. - : Wiley. - 1862-6300. ; 203:7, s. 1672-1675
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Journal article (peer-reviewed)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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| 2. |
- Amare, Azmeraw T, et al.
(author)
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Association of polygenic score and the involvement of cholinergic and glutamatergic pathways with lithium treatment response in patients with bipolar disorder.
- 2023
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In: Molecular psychiatry. - 1476-5578. ; 28, s. 5251-5261
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Journal article (peer-reviewed)abstract
- Lithium is regarded as the first-line treatment for bipolar disorder (BD), a severe and disabling mental healthdisorder that affects about 1% of the population worldwide. Nevertheless, lithium is not consistently effective, with only 30% of patients showing a favorable response to treatment. To provide personalized treatment options for bipolar patients, it is essential to identify prediction biomarkers such as polygenic scores. In this study, we developed a polygenic score for lithium treatment response (Li+PGS) in patients with BD. To gain further insights into lithium's possible molecular mechanism of action, we performed a genome-wide gene-based analysis. Using polygenic score modeling, via methods incorporating Bayesian regression and continuous shrinkage priors, Li+PGS was developed in the International Consortium of Lithium Genetics cohort (ConLi+Gen: N=2367) and replicated in the combined PsyCourse (N=89) and BipoLife (N=102) studies. The associations of Li+PGS and lithium treatment response - defined in a continuous ALDA scale and a categorical outcome (good response vs. poor response) were tested using regression models, each adjusted for the covariates: age, sex, and the first four genetic principal components. Statistical significance was determined at P<0.05. Li+PGS was positively associated with lithium treatment response in the ConLi+Gen cohort, in both the categorical (P=9.8×10-12, R2=1.9%) and continuous (P=6.4×10-9, R2=2.6%) outcomes. Compared to bipolar patients in the 1st decile of the risk distribution, individuals in the 10th decile had 3.47-fold (95%CI: 2.22-5.47) higher odds of responding favorably to lithium. The results were replicated in the independent cohorts for the categorical treatment outcome (P=3.9×10-4, R2=0.9%), but not for the continuous outcome (P=0.13). Gene-based analyses revealed 36 candidate genes that are enriched in biological pathways controlled by glutamate and acetylcholine. Li+PGS may be useful in the development of pharmacogenomic testing strategies by enabling a classification of bipolar patients according to their response to treatment.
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| 3. |
- Paskov, Plamen, 1959-, et al.
(author)
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Optical properties of nonpolar a-plane GaN layers
- 2006
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In: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 40:4-6 SPEC. ISS., s. 253-261
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Journal article (peer-reviewed)abstract
- We have studied optical properties of nonpolar a-plane GaN layers grown on r-plane sapphire by metalorganic chemical vapor deposition and hydride vapor phase epitaxy using different nucleation schemes. Several emission bands, which are not typical for c-plane GaN, are observed in the photoluminescence spectra and their excitation-intensity, temperature, and polarization dependencies are examined. In addition, the spatial distribution of the emissions was examined by cathodoluminescence imaging and relations of the different emissions with particular structural features in the layers are revealed. The results are discussed with emphasis on the origin of the emission line and particular recombination mechanisms. © 2006 Elsevier Ltd. All rights reserved.
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| 4. |
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| 5. |
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| 6. |
- Roder, C., et al.
(author)
-
Stress and wafer bending of a -plane GaN layers on r -plane sapphire substrates
- 2006
-
In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 100:10
-
Journal article (peer-reviewed)abstract
- The stress and wafer bending of (11 2- 0) a -plane GaN layers of different thicknesses grown on (1 1- 02) r -plane sapphire substrates by hydride vapor phase epitaxy were studied by high-resolution x-ray diffraction and photoluminescence and photoreflectance spectroscopies. The layers are found to be under compression in the growth plane and under tension in the growth direction. The elastic and thermal anisotropies of the GaN and the sapphire crystal result in an in-plane stress and a wafer curvature, both of which are different in the two in-plane directions parallel and perpendicular to the GaN c axis. The GaN unit cell is no longer hexagonal but orthorhombic. The stress relaxes with increasing GaN layer thickness while the curvature of the wafer increases. Different stress relief mechanisms are considered, and the stresses in the layer and the curvature of the wafer are calculated using standard models on wafer bending. The results suggest that the wafer bending is the dominant stress relief mechanism. In addition, the redshift of the near-band-edge photoluminescence and the free exciton photoreflectance peaks with increasing layer thickness is correlated with the strain data determined by x-ray diffraction. © 2006 American Institute of Physics.
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| 7. |
- Yarza, P., et al.
(author)
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Sequencing orphan species initiative (SOS): Filling the gaps in the 16S rRNA gene sequence database for all species with validly published names
- 2013
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In: Systematic and Applied Microbiology. - : Elsevier BV. - 0723-2020. ; 36:1, s. 69-73
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Journal article (peer-reviewed)abstract
- High quality 16S ribosomal RNA (rRNA) gene sequences from the type strains of all species with validly published names, as defined by the International Code of Nomenclature of Bacteria, are a prerequisite for their accurate affiliations within the global genealogical classification and for the recognition of potential new taxa. During the last few years, the Living Tree Project (LTP) has taken care to create a high quality, aligned 16S and 23S rRNA gene sequence database of all type strains. However, the manual curation of the sequence dataset and type strain information revealed that a total of 552 “orphan” species (about 5.7% of the currently classified species) had to be excluded from the reference trees. Among them, 322 type strains were not represented by an SSU entry in the public sequence repositories. The remaining 230 type strains had to be discarded due to bad sequence quality. Since 2010, the LTP team has coordinated a network of researchers and culture collections in order to improve the situation by (re)-sequencing the type strains of these “orphan” species. As a result, we can now report 351 16S rRNA gene sequences of type strains. Nevertheless, 201 species could not be sequenced because cultivable type strains were not available (121), the cultures had either been lost or were never deposited in the first place (66), or it was not possible due to other constraints (14). The International Code of Nomenclature of Bacteria provides a number of mechanisms to deal with the problem of missing type strains and we recommend that due consideration be given to the appropriate mechanisms in order to help solve some of these issues.
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| 8. |
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| 9. |
- Darakchieva, Vanya, et al.
(author)
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Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a-plane GaN
- 2006
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In: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1594-1598
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Journal article (peer-reviewed)abstract
- Generalized infrared spectroscopic ellipsometry was applied to study the vibrational properties of anisotropically strained a-plane GaN films with different thicknesses. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and strain-free frequency of the GaN A,(TO) mode. These results are compared with previous theoretical and experimental findings and discussed.
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| 10. |
- Kalman, Janos L, et al.
(author)
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Investigating polygenic burden in age at disease onset in bipolar disorder: Findings from an international multicentric study.
- 2019
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In: Bipolar disorders. - : Wiley. - 1399-5618 .- 1398-5647. ; 21:1, s. 68-75
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Journal article (peer-reviewed)abstract
- Bipolar disorder (BD) with early disease onset is associated with an unfavorable clinical outcome and constitutes a clinically and biologically homogenous subgroup within the heterogeneous BD spectrum. Previous studies have found an accumulation of early age at onset (AAO) in BD families and have therefore hypothesized that there is a larger genetic contribution to the early-onset cases than to late onset BD. To investigate the genetic background of this subphenotype, we evaluated whether an increased polygenic burden of BD- and schizophrenia (SCZ)-associated risk variants is associated with an earlier AAO in BD patients.A total of 1995 BD type 1 patients from the Consortium of Lithium Genetics (ConLiGen), PsyCourse and Bonn-Mannheim samples were genotyped and their BD and SCZ polygenic risk scores (PRSs) were calculated using the summary statistics of the Psychiatric Genomics Consortium as a training data set. AAO was either separated into onset groups of clinical interest (childhood and adolescence [≤18years] vs adulthood [>18years]) or considered as a continuous measure. The associations between BD- and SCZ-PRSs and AAO were evaluated with regression models.BD- and SCZ-PRSs were not significantly associated with age at disease onset. Results remained the same when analyses were stratified by site of recruitment.The current study is the largest conducted so far to investigate the association between the cumulative BD and SCZ polygenic risk and AAO in BD patients. The reported negative results suggest that such a polygenic influence, if there is any, is not large, and highlight the importance of conducting further, larger scale studies to obtain more information on the genetic architecture of this clinically relevant phenotype.
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| 11. |
- Monemar, Bo, 1942-, et al.
(author)
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Optical signatures of dopants in GaN
- 2006
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In: Materials Science in Semiconductor Processing. - : Elsevier BV. - 1369-8001 .- 1873-4081. ; 9:1-3, s. 168-174
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Journal article (peer-reviewed)abstract
- The characteristic optical spectra for shallow donors and acceptors in GaN are discussed. The most accurate photoluminescence (PL) data are obtained from samples grown on freestanding GaN substrates, where strain shifts are absent and a low spectroscopic line width is obtained. Recent PL data for excitons bound to the O and Si donors are discussed in some detail, giving accurate values for the binding energies and excited bound donor states. The Mg-acceptor is the most important one for p-doping, but the related optical spectra are controversial. We show that there are two acceptors present in Mg-doped GaN, with two different acceptor bound exciton peaks, and also two corresponding lower energy donor-acceptor pair spectra. We give tentative evidence for their interpretation. © 2006 Elsevier Ltd. All rights reserved.
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| 12. |
- Chakraborty, Jishnunil, et al.
(author)
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Synthesis, crystal, and molecular structure of coordination polymers constructed by self-assembly of NiN4 cores with 2,2 '-iminodibenzoate and nitroprusside ions
- 2007
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In: Structural Chemistry. - : Springer Science and Business Media LLC. - 1040-0400 .- 1572-9001. ; 18:2, s. 157-164
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Journal article (peer-reviewed)abstract
- Two coordination compounds of compositions [Ni(L-1)(idba)(H2O)]center dot 1.5 H2O (1) and [Ni(L-2)Fe(CN)(5)NO]. C2H5OH (2) where L-1 is N, N-bis(3-aminopropyl)ethylenediamine, L-2 is 2,12-dimethyl-3,7,11,17-tetraazabicyclo [11.3.1]heptadeca-1(17),2,11,13,15-pentaene, and idba(2)- is 2,2'-iminodibenzoate have been synthesized and characterized by elemental analysis, IR spectroscopy, thermal analysis, and single-crystal X-ray diffraction. Complex I crystallizes in the monoclinic space group P2(1)/n (No. 14) with a = 9.810(2) angstrom, b = 10.230(2) angstrom, c = 25.350(5) angstrom, V = 2543.6(9) angstrom(3), Z = 4, and R = 0.0727. The nickel atom is six-coordinated by four N atoms of amine and two 0 atoms of water and idba2-. The molecular packing of the complex comprises of an infinite one-dimensional layered network in which the molecules in the crystal are held together by a system of hydrogen bonding. Complex 2, however, crystallizes in the space group C2/c (No. 15) of the monoclinic system with a = 19.7990(4) angstrom, b = 14.9440(3) angstrom, c = 19.8800(3) angstrom, V = 5115.90(17) angstrom(3), Z = 4, and R = 0.0540. The Ni ion in compound 2 has a slightly distorted octahedral arrangement of the N-4 donor atoms of primary ligand L-2 and two N-donor atoms of the secondary nitroprusside ligand. The structure of 2 displays an extended one-dimensional network formed by linear [-Ni-NC-Fe-CN-] units. A cyclic voltammetric study shows that compound 1 undergoes a quasireversible oxidation attributable to Ni2+ -> Ni3+ in the range 300-420 mV vs SCE.
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| 13. |
- Figge, S, et al.
(author)
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Optoelectronic devices on bulk GaN
- 2005
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 281:1, s. 101-106
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Journal article (peer-reviewed)abstract
- The homoeptaxial fabrication of GaN-based devices has advantages against heteroepitaxial realization on substrates such as sapphire or SiC, since heteroepitaxy implies a lot of problems like lattice mismatch, different thermal expansion coefficients, and needs an extensive optimization of the growth at the heterointerface. In this paper we will discuss GaN-based light-emitting devices grown by homoepitaxy in comparison to devices grown on sapphire. A special emphasis is laid on the pretreatment of the GaN substrate and the device characteristics on different substrates. In detail will be discussed the advantages of the higher thermal conductivity of GaN and how this effects the device performance. (c) 2005 Elsevier B.V. All rights reserved.
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| 14. |
- Kroger, R., et al.
(author)
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Interfacial structure of a -plane GaN grown on r -plane sapphire
- 2007
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:8
-
Journal article (peer-reviewed)abstract
- The interface between a -plane GaN, grown by metal organic vapor phase epitaxy and hydride vapor phase epitaxy, and r -plane sapphire was investigated by transmission electron microscopy in [1-100] and [0001] zone axis orientations. The interfacial structure was well defined allowing a direct observation of the misfit dislocations in both orientations. An analysis of these dislocations revealed for the respective Burgers vectors a 13 <2-1-10> component in the {0002} planes and a 12 <0001> component in the {1-100} planes. In addition, the relative atomic column configurations in the GaN and sapphire were determined based on Bloch-wave simulations in comparison with the experimental images. © 2007 American Institute of Physics.
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| 15. |
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| 16. |
- Monemar, Bo, et al.
(author)
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Evidence for Two Mg Related Acceptors in GaN
- 2009
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In: PHYSICAL REVIEW LETTERS. - 0031-9007 .- 1079-7114. ; 102:23, s. 235501-
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Journal article (peer-reviewed)abstract
- The optical signatures of Mg-related acceptors in GaN have been revisited in samples specifically grown on bulk GaN templates, to avoid strain broadening of the optical spectra. Bound-exciton spectra can be studied in these samples for Mg concentrations up to [Mg]approximate to 2x10(19) cm(-3). Contrary to previous work it is found that instabilities in the photoluminescence spectra are not due to unstable shallow donors, but to unstable Mg-related acceptors. Our data show that there are two Mg-related acceptors simultaneously present: the regular (stable) substitutional Mg acceptor, and a complex acceptor which is unstable in p-GaN.
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| 17. |
- Monemar, Bo, et al.
(author)
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Mg related acceptors in GaN
- 2010
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In: Phys. Status Solidi C 7. ; , s. 1850-
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Conference paper (peer-reviewed)
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| 18. |
- Monemar, Bo, et al.
(author)
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The dominant shallow 0.225 eV acceptor in GaN
- 2006
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In: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1604-1608
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Journal article (peer-reviewed)abstract
- We have studied the optical signatures of the Mg acceptor in GaN, using samples that are doped with Mg during MOCVD growth. In order to reduce the defect density in the material and thus achieve narrow linewidths in optical spectra we have used thick HVPE grown GaN layers as templates in the MOCVD growth. The photoluminescence (PL) spectra show two acceptor-related bound exciton peaks at 3.466 eV and 3.455 eV respectively. In the lower photon energy range the 3.27 eV emission with its LO-phonon replicas is dominant, riding on a broad background emission peaking at about 3.1 eV. These results, together with previous data in the literature, indicate that there are two acceptors in Mg-doped GaN, one dominating the optical spectra (the 3.466 eV and the 3.27 eV emissions) and another related to the 3.455 eV and the 3.1 eV emissions. We suggest that the latter is related to the Mg acceptor, while the former is a H-related complex, not necessarily involving Mg.
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| 19. |
- Paskov, Plamen, et al.
(author)
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Emission properties of a -plane GaN grown by metal-organic chemical-vapor deposition
- 2005
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 98:9, s. 093519-
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Journal article (peer-reviewed)abstract
- We report on the emission properties of nonpolar a -plane GaN layers grown on r -plane sapphire. Temperature-, excitation-density-, and polarization-dependent photoluminescences and spatially resolved microphotoluminescence and cathodoluminescence are employed in order to clarify the nature of the different emission bands in the 3.0-3.5 eV spectral range. In the near band-edge region the emission lines of the donor-bound excitons (3.472 eV) and free excitons (3.478 eV) are resolved in the polarized low-temperature spectra, indicating a good quality of the layers. At low energies two other emissions bands with intensity and shape varying with the excited area are observed. The 3.42 eV emission commonly attributed to the excitons bound to basal plane stacking faults shows thermal quenching with two activation energies (7 and 30 meV) and an S-shaped temperature dependence of the peak position. This behavior is analyzed in terms of hole localization in the vicinity of the stacking faults. The emission band that peaked at 3.29 eV is found to blueshift and saturate with increasing excitation intensity. The spatially resolved cathodoluminesence measurements show that the emission is asymmetrically distributed around the triangular-shaped pits occurring at the surface. The 3.29 eV emission is suggested to involve impurities, which decorate the partial dislocation terminating the basal stacking faults. © 2005 American Institute of Physics.
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| 20. |
- Paskov, Plamen, et al.
(author)
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Structural defect-related emissions in nonpolar a-plane GaN
- 2006
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In: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 376, s. 473-476
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Journal article (peer-reviewed)abstract
- We have studied the optical emission properties of a-plane GaN layers grown on r-plane sapphire by metalorganic chemical vapor deposition. Together with the typical band edge exciton emission, the photoluminescence (PL) spectra reveal three low-energy emissions peaked at 3.42, 3.34 and 3.29eV. which are related to structural defects. Temperature and excitation dependent stationary PL and the time-resolved PL have been employed in order to understand the exact origin of these emissions. The 3.42 and 3.34eV emissions are found to be of an intrinsic origin and are associated with carriers localized at stacking faults. The emission at 3.29eV shows a donor-acceptor pair behavior suggesting that impurities attached to structural defects most likely partial dislocations terminating stacking faults are involved. (c) 2005 Elsevier B.V. All rights reserved.
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| 21. |
- Paskova, T., et al.
(author)
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High-quality bulk a-plane GaN sliced from boules in comparison to heteroepitaxially grown thick films on r-plane sapphire
- 2006
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:5, s. 051914-
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Journal article (peer-reviewed)abstract
- Thick GaN bars with [1120] orientation have been sliced from GaN boules grown on freestanding films by hydride vapor phase epitaxy (HVPE) in the [0001] direction. High-resolution x-ray diffraction and transmission electron microscopy have been used to study the structural quality and defect distribution in the material in comparison to heteroepitaxially grown thick HVPE-GaN films grown in the [1120] direction on (1102)-plane sapphire. It is demonstrated that while the heteroepitaxial material possesses a high density of stacking faults and partial dislocations, leading to anisotropic structural characteristics, the (1120)-plane bulk GaN, sliced from boules, exhibits low dislocation density and narrow rocking curves with isotropic in-plane character. © 2006 American Institute of Physics.
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| 22. |
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| 23. |
- Tuomisto, F., et al.
(author)
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Defect distribution in a-plane GaN on Al2 O3
- 2007
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:12
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Journal article (peer-reviewed)abstract
- The authors studied the structural and point defect distributions of hydride vapor phase epitaxial GaN film grown in the [11-20] a direction on (1-102) r -plane sapphire with metal-organic vapor phase deposited a-GaN template using transmission electron microscopy, secondary ion mass spectrometry, and positron annihilation spectroscopy. Grown-in extended and point defects show constant behavior as a function of thickness, contrary to the strong nonuniform defect distribution observed in GaN grown along the [0001] direction. The observed differences are explained by orientation-dependent and kinetics related defect incorporation. © 2007 American Institute of Physics.
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| 24. |
- Tuomisto, F., et al.
(author)
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Vacancy defect distribution in heteroepitaxial a-plane GaN grown by hydride vapor phase epitaxy
- 2007
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 300:1, s. 251-253
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Journal article (peer-reviewed)abstract
- We have used positron annihilation spectroscopy to study the native vacancy distribution in a-plane heteroepitaxial GaN. We show that the Ga vacancy concentration is independent of the layer thickness in the range from 5 to 25 µ m. This is strikingly different from the behavior in c-plane GaN, where the Ga vacancy concentration decreases dramatically with the distance from the GaN/sapphire interface. This difference in the native vacancy profiles is tentatively correlated with the differences in the O impurity and dislocation density profiles in the polar and non-polar materials. © 2006 Elsevier B.V. All rights reserved.
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