| 1. |
- dos Santos, R. B., et al.
(författare)
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Dopant species with Al-Si and N-Si bonding in the MOCVD of AlN implementing trimethylaluminum, ammonia and silane
- 2015
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Ingår i: Journal of Physics D. - : IOP Publishing: Hybrid Open Access. - 0022-3727 .- 1361-6463. ; 48:29
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated gas-phase reactions driven by silane (SiH4), which is the dopant precursor in the metalorganic chemical vapor deposition (MOCVD) of aluminum nitride (AlN) doped by silicon, with prime focus on determination of the associated energy barriers. Our theoretical strategy is based on combining density-functional methods with minimum energy path calculations. The outcome of these calculations is suggestive for kinetically plausible and chemically stable reaction species with Al-Si bonding such as (CH3)(2)AlSiH3 and N-Si bonding such as H2NSiH3. Within this theoretical perspective, we propose a view of these reaction species as relevant for the actual MOCVD of Si-doped AlN, which is otherwise known to be contributed by the reaction species (CH3)(2)AlNH2 with Al-N bonding. By reflecting on experimental evidence in the MOCVD of various doped semiconductor materials, it is anticipated that the availability of dopant species with Al-Si, and alternatively N-Si bonding near the hot deposition surface, can govern the incorporation of Si atoms, as well as other point defects, at the AlN surface.
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| 2. |
- dos Santos, Renato B., et al.
(författare)
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Feasibility of novel (H3C)(n)X(SiH3)(3-n) compounds (X = B, Al, Ga, In): structure, stability, reactivity, and Raman characterization from ab initio calculations
- 2015
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 44:7, s. 3356-3366
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Tidskriftsartikel (refereegranskat)abstract
- We employ ab initio calculations to predict the equilibrium structure, stability, reactivity, and Raman scattering properties of sixteen different (H3C)(n)X(SiH3)(3-n) compounds (X = B, Al, Ga, In) with n = 0-3. Among this methylsilylmetal family, only the (H3C)(3)X members, i.e., trimethylboron (TMB), trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI), are currently well-studied. The remaining twelve compounds proposed here open up a two-dimensional array of new possibilities for precursors in various deposition processes, and evoke potential applications in the chemical synthesis of other compounds. We infer that within the (H3C)(n)X(SiH3)(3-n) family, the compounds with fewer silyl groups (and consequently with more methyl groups) are less reactive and more stable. This trend is verified from the calculated cohesive energy, Gibbs free energy of formation, bond strength, and global chemical indices. Furthermore, we propose sequential reaction routes for the synthesis of (H3C)(n)X(SiH3)(3-n) by substitution of methyl by silyl groups, where the silicon source is the silane gas. The corresponding reaction barriers for these chemical transformations lie in the usual energy range typical for MOCVD processes. We also report the Raman spectra and light scattering properties of the newly proposed (H3C)(n)X(SiH3)(3-n) compounds, in comparison with available data of known members of this family. Thus, our computational experiment provides useful information for a systematic understanding of the stability/reactivity and for the identification of these compounds.
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| 3. |
- dos Santos, Renato B., et al.
(författare)
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Van der Waals stacks of few-layer h-AlN with graphene: an ab initio study of structural, interaction and electronic properties
- 2016
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Ingår i: Nanotechnology. - : IOP PUBLISHING LTD. - 0957-4484 .- 1361-6528. ; 27:14, s. 145601-
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Tidskriftsartikel (refereegranskat)abstract
- Graphite-like hexagonal AlN (h-AlN) multilayers have been experimentally manifested and theoretically modeled. The development of any functional electronics applications of h-AlN would most certainly require its integration with other layered materials, particularly graphene. Here, by employing vdW-corrected density functional theory calculations, we investigate structure, interaction energy, and electronic properties of van der Waals stacking sequences of few-layer h-AlN with graphene. We find that the presence of a template such as graphene induces enough interlayer charge separation in h-AlN, favoring a graphite-like stacking formation. We also find that the interface dipole, calculated per unit cell of the stacks, tends to increase with the number of stacked layers of h-AlN and graphene.
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| 4. |
- Feneberg, Martin, et al.
(författare)
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Exciton luminescence in AIN triggered by hydrogen and thermal annealing
- 2015
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 106:24, s. 242101-
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Tidskriftsartikel (refereegranskat)abstract
- Exciton recombination bands in homoepitaxial AIN layers are strongly dependent on the presence of hydrogen. By thermal treatment under hydrogen-free and hydrogen-rich ambient, respectively, several sharp bound exciton lines are modulated in intensity reversibly. In contrast, the exciton bound at the neutral donor silicon remains unaffected. The mechanism causing these effects is most probably hydrogen in-and out-diffusion into the AIN sample. The main factor determining hydrogenation of AIN layers is found to be molecular H-2 in contrast to NH3. We find hints that carbon incorporation into AIN may be closely related with that of hydrogen. Besides photoluminescence spectra of exciton bands, our model is supported by theoretical reports and comparison to the case of hydrogen in GaN.
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| 5. |
- Freitas, Rafael RQ, et al.
(författare)
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Tuning band inversion symmetry of buckled III-Bi sheets by halogenation
- 2016
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Ingår i: Nanotechnology. - : IOP PUBLISHING LTD. - 0957-4484 .- 1361-6528. ; 27:5, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- First-principles calculations are employed to investigate structural, electronic and topological insulating properties of XBi (X = B, Al, Ga, and In) monolayers upon halogenation. It is known that Y-XBi (X = Ga, In, Tl; Y = F, Cl, Br, I) can originate inversion-asymmetric topological insulators with large bulk band gaps. Our results suggest that Y-XBi (X = B, Al; Y = F, Cl, Br, I) may also result in nontrivial topological insulating phases. Despite the lower atomic number of B and Al, the spin-orbit coupling opens a band gap of about 400 meV in Y-XBi (X = B, Al), exhibiting an unusual electronic behavior for practical applications in spintronics. The nature of the bulk band gap and Dirac-cone edge states in their nanoribbons depends on the group-III elements and Y chemical species. They lead to a chemical tunability, giving rise to distinct band inversion symmetries and exhibiting Rashba-type spin splitting in the valence band of these systems. These findings indicate that a large family of Y-XBi sheets can exhibit nontrivial topological characteristics, by a proper tuning, and open a new possibility for viable applications at room temperature.
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| 6. |
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| 7. |
- Kakanakova-Gueorguie, Anelia, et al.
(författare)
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n-Type conductivity bound by the growth temperature: the case of Al0.72Ga0.28N highly doped by silicon
- 2016
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Ingår i: Journal of Materials Chemistry C. - : ROYAL SOC CHEMISTRY. - 2050-7526 .- 2050-7534. ; 4:35, s. 8291-8296
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Tidskriftsartikel (refereegranskat)abstract
- High-Al-content AlxGa(1-x)N layers, x similar to 0.72, have been grown by metal organic chemical vapour deposition (MOCVD) at a temperature ranging from 1000 to 1100 degrees C, together with high flow rate of the dopant precursor silane (SiH4) in order to obtain highly Si-doped Al0.72Ga0.28N layers, similar to 1 x 10(19) cm(-3) as measured by secondary ion mass spectrometry (SIMS). Further characterization of the layers by capacitance-voltage (C-V), electron paramagnetic resonance (EPR), and transmission electron microscopy (TEM) measurements reveals the complex role of growth temperature for the n-type conductivity of high-Al-content AlxGa1-xN. While increasing temperature is essential for reducing the incorporation of carbon and oxygen impurities in the layers, it also reduces the amount of silicon incorporated as a donor.
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| 8. |
- Kakanakova-Gueorguie, Anelia, et al.
(författare)
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Silicon and oxygen in high-Al-content AlGaN: incorporation kinetics and electron paramagnetic resonance study
- 2014
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Ingår i: Gettering and Defect Engineering in Semiconductor Technology XV. - : Trans Tech Publications Inc.. ; , s. 441-445
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Konferensbidrag (refereegranskat)abstract
- The high-Al-content AlxGa1-xN alloys, xgreater than0.70, and AlN is the fundamental wide-band-gap material system associated with the technology development of solid-state LEDs operating at the short wavelengths in the deep-UV (lambda less than 280 nm). Yet, their properties are insufficiently understood. The present study is intended to bring elucidation on the long-time debated and much speculated Si transition from shallow donor in GaN to a localized deep DX defect in AlxGa1-xN alloys with increasing Al content. For that purpose electron paramagnetic resonance is performed on a particular selection of high-Al-content epitaxial layers of Al0.77Ga0.23N, alternatively Al0.72Ga0.28N, alloy composition.
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| 9. |
- Schoche, S., et al.
(författare)
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Infrared dielectric functions, phonon modes, and free-charge carrier properties of high-Al-content AlxGa1-xN alloys determined by mid infrared spectroscopic ellipsometry and optical Hall effect
- 2017
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 121:20
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Tidskriftsartikel (refereegranskat)abstract
- We report on the analysis of a combined mid-infrared spectroscopic ellipsometry and mid-infrared optical Hall effect investigation of wurtzite structure c-plane oriented, crack-free, single crystalline, and high-Al-content AlxGa1-xN layers on 4H-SiC. For high-Al-content AlxGa1-xN, a two mode behavior is observed for both transverse and longitudinal branches of the infrared-active modes with E-1 symmetry, while a single mode behavior is found for the longitudinal modes with A1(LO) symmetry. We report their mode dependencies on the Al content. We determine and discuss static and high frequency dielectric constants depending on x. From the analysis of the optical Hall effect data, we determine the effective mass parameter in high-Al-content AlxGa1-xN alloys and its composition dependence. Within the experimental uncertainty limits, the effective mass parameters are found isotropic, which depend linearly on the Al content. The combination of all data permits the quantification of the free electron density N and mobility parameters mu. Published by AIP Publishing.
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| 10. |
- Schoeche, S, et al.
(författare)
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Electron effective mass in Al0.72Ga0.28N alloys determined by mid-infrared optical Hall effect
- 2013
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 103:21, s. 212107-
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Tidskriftsartikel (refereegranskat)abstract
- The effective electron mass parameter in Si-doped Al0.72Ga0.28N is determined to be m* = (0.336 +/- 0.020) m(0) from mid-infrared optical Hall effect measurements. No significant anisotropy of the effective electron mass parameter is found supporting theoretical predictions. Assuming a linear change of the effective electron mass with the Al content in AlGaN alloys and m* = 0.232m(0) for GaN, an average effective electron mass of m* = 0.376m(0) can be extrapolated for AlN. The analysis of mid-infrared spectroscopic ellipsometry measurements further confirms the two phonon mode behavior of the E-1(TO) and one phonon mode behavior of the A(1)(LO) phonon mode in high-Al-content AlGaN alloys as seen in previous Raman scattering studies.
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