The Experts below are selected from a list of 85590 Experts worldwide ranked by ideXlab platform
Minjoo Lawrence Lee - One of the best experts on this subject based on the ideXlab platform.
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high efficiency algainp solar cells grown by Molecular Beam epitaxy
Applied Physics Letters, 2016Co-Authors: Joseph Faucher, Yanning Sun, Daehwan Jung, D Martin, Taizo Masuda, Minjoo Lawrence LeeAbstract:AlGaInP is an ideal material for ultra-high efficiency, lattice-matched multi-junction solar cells grown by Molecular Beam epitaxy (MBE) because it can be grown lattice-matched to GaAs with a wide 1.9–2.2 eV bandgap. Despite this potential, AlGaInP grown by Molecular Beam epitaxy (MBE) has yet to be fully explored, with the initial 2.0 eV devices suffering from poor performance due to low minority carrier diffusion lengths in both the emitter and base regions of the solar cell. In this work, we show that implementing an AlGaInP graded layer to introduce a drift field near the front surface of the device enabled greatly improved internal quantum efficiency (IQE) across all wavelengths. In addition, optimizing growth conditions and post-growth annealing improved the long-wavelength IQE and the open-circuit voltage of the cells, corresponding to a 3× increase in diffusion length in the base. Taken together, this work demonstrates greatly improved IQE, attaining peak values of 95%, combined with an uncoated AM1.5G efficiency of 10.9%, double that of previously reported MBE-grown devices.
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gaasp solar cells on gap substrates by Molecular Beam epitaxy
Applied Physics Letters, 2012Co-Authors: Stephanie Tomasulo, Nay K Yaung, John Simon, Minjoo Lawrence LeeAbstract:We demonstrate Molecular Beam epitaxy (MBE) of GaAsxP1−x/GaP solar cells over a range of bandgap energies (Eg). Identical GaAs0.66P0.34 cells on GaAs and GaP exhibit similar properties; GaAs0.66P0.34/GaP cells with Eg = 1.82 eV produced an open-circuit voltage (Voc) of 1.24 V, ∼40 mV lower than previous GaAs0.66P0.34/GaAs cells. We then grew GaAs0.56P0.44/GaP cells with Eg = 1.92 eV to investigate their suitability for wide-Eg applications, reaching Voc = 1.27 V. For potential dual-junction integration on Si, we grew Eg = 1.71 eV GaAs0.73P0.27/GaP cells, attaining Voc = 1.15 V. These results indicate that GaAsxP1−x/GaP solar cells by MBE are promising for integration onto Si and for other photovoltaic applications.
D G Schlom - One of the best experts on this subject based on the ideXlab platform.
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constructing oxide interfaces and heterostructures by atomic layer by layer laser Molecular Beam epitaxy
npj Quantum Materials, 2017Co-Authors: Maryam Golalikhani, B A Davidson, D G Schlom, Qiao Qiao, Ravini U Chandrasena, Weibing Yang, A X Gray, Elke Arenholz, A K FarrarAbstract:Advancements in nanoscale engineering of oxide interfaces and heterostructures have led to discoveries of emergent phenomena and new artificial materials. Combining the strengths of reactive Molecular-Beam epitaxy and pulsed-laser deposition, we show here, with examples of Sr1+x Ti1-x O3+δ, Ruddlesden–Popper phase La n+1Ni n O3n+1 (n = 4), and LaAl1+y O3(1+0.5y)/SrTiO3 interfaces, that atomic layer-by-layer laser Molecular-Beam epitaxy significantly advances the state of the art in constructing oxide materials with atomic layer precision and control over stoichiometry. With atomic layer-by-layer laser Molecular-Beam epitaxy we have produced conducting LaAlO3/SrTiO3 interfaces at high oxygen pressures that show no evidence of oxygen vacancies, a capability not accessible by existing techniques. The carrier density of the interfacial two-dimensional electron gas thus obtained agrees quantitatively with the electronic reconstruction mechanism. Recent advances in synthesizing and engineering oxide interfaces and heterostructures have provided a powerful strategy for creating new artificial structures exhibiting phenomena not possible in other materials form. Now Professor Xiaoxing Xi at Temple University from the US collaborates with researchers from the US, Italy and China showing a success in constructing oxides with well controlled stoichiometry and atomic layer precision. The central method—atomic layer-by-layer laser Molecular Beam epitaxy (ALL-Laser MBE)—is built upon the combined strengths of Molecular Beam epitaxy and pulsed laser deposition. It allows not only the growth of thin films of a Ruddlesden-Popper phase La5Ni4O13, but LaAlO3/SrTiO3 interfaces. Remarkably, no oxygen vacancies are detected in the oxide interfaces because of the high oxygen pressures during the growth and the carrier density of the two-dimensional electron gas agrees with the electronic reconstruction mechanism.
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constructing oxide interfaces and heterostructures by atomic layer by layer laser Molecular Beam epitaxy
arXiv: Mesoscale and Nanoscale Physics, 2016Co-Authors: Maryam Golalikhani, B A Davidson, D G Schlom, Qiao Qiao, Ravini U Chandrasena, Weibing Yang, A X Gray, Elke Arenholz, A K FarrarAbstract:Advancements in nanoscale engineering of oxide interfaces and heterostructures have led to discoveries of emergent phenomena and new artificial materials. Combining the strengths of reactive Molecular-Beam epitaxy and pulsed-laser deposition, we show here, with examples of Sr1+xTi1-xO3+delta, Ruddlesden-Popper phase Lan+1NinO3n+1 (n = 4), and LaAl1+yO3(1+0.5y)/SrTiO3 interfaces, that atomic layer-by-layer laser Molecular-Beam epitaxy (ALL-Laser MBE) significantly advances the state of the art in constructing oxide materials with atomic layer precision and control over stoichiometry. With ALL-Laser MBE we have produced conducting LaAlO3/SrTiO3 interfaces at high oxygen pressures that show no evidence of oxygen vacancies, a capability not accessible by existing techniques. The carrier density of the interfacial two-dimensional electron gas thus obtained agrees quantitatively with the electronic reconstruction mechanism.
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growth of homoepitaxial srtio3 thin films by Molecular Beam epitaxy
Applied Physics Letters, 2009Co-Authors: Charles M Brooks, T Heeg, J Schubert, Fitting L Kourkoutis, David A Muller, D G SchlomAbstract:We report the structural properties of homoepitaxial (100) SrTiO3 films grown by reactive Molecular-Beam epitaxy (MBE). The lattice spacing and x-ray diffraction (XRD) rocking curves of stoichiometric MBE-grown SrTiO3 films are indistinguishable from the underlying SrTiO3 substrates. Off-stoichiometry for both strontium-rich and strontium-poor compositions (i.e., Sr1+xTiO3+δ films with −0.2
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adsorption controlled Molecular Beam epitaxial growth of bifeo3
Applied Physics Letters, 2007Co-Authors: Jon F Ihlefeld, D G Schlom, T Heeg, Y B Chen, J Schubert, Amit Kumar, Venkatraman Gopalan, Xiaoqing Pan, P Schiffer, J OrensteinAbstract:BiFeO3 thin films have been deposited on (111) SrTiO3 single crystal substrates by reactive Molecular-Beam epitaxy in an adsorption-controlled growth regime. This is achieved by supplying a bismuth overpressure and utilizing the differential vapor pressures between bismuth oxides and BiFeO3 to control stoichiometry. Four-circle x-ray diffraction reveals phase-pure, untwinned, epitaxial, (0001)-oriented films with rocking curve full width at half maximum values as narrow as 25arcsec (0.007°). Second harmonic generation polar plots combined with diffraction establish the crystallographic point group of these untwinned epitaxial films to be 3m at room temperature.
J Schubert - One of the best experts on this subject based on the ideXlab platform.
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ferroelectric properties of ion irradiated bismuth ferrite layers grown via Molecular Beam epitaxy
APL Materials, 2019Co-Authors: Antonio B Mei, J Schubert, Sahar Saremi, Ludi Miao, Matthew R Barone, Yongjian Tang, Cyrus Zeledon, D C Ralph, Lane W MartinAbstract:We systematically investigate the role of defects, introduced by varying synthesis conditions and by carrying out ion irradiation treatments, on the structural and ferroelectric properties of commensurately strained bismuth ferrite BixFe2−xO3 layers grown on SrRuO3-coated DyScO3(110)o substrates using adsorption-controlled ozone Molecular-Beam epitaxy. Our findings highlight ion irradiation as an effective approach for reducing through-layer electrical leakage, a necessary condition for the development of reliable ferroelectrics-based electronics.
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growth of homoepitaxial srtio3 thin films by Molecular Beam epitaxy
Applied Physics Letters, 2009Co-Authors: Charles M Brooks, T Heeg, J Schubert, Fitting L Kourkoutis, David A Muller, D G SchlomAbstract:We report the structural properties of homoepitaxial (100) SrTiO3 films grown by reactive Molecular-Beam epitaxy (MBE). The lattice spacing and x-ray diffraction (XRD) rocking curves of stoichiometric MBE-grown SrTiO3 films are indistinguishable from the underlying SrTiO3 substrates. Off-stoichiometry for both strontium-rich and strontium-poor compositions (i.e., Sr1+xTiO3+δ films with −0.2
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optical band gap of bifeo3 grown by Molecular Beam epitaxy
Applied Physics Letters, 2008Co-Authors: Jon F Ihlefeld, Nikolas J Podraza, Zikui Liu, R C Rai, T Heeg, Y B Chen, Robert W Collins, J L Musfeldt, X Q Pan, J SchubertAbstract:BiFeO3 thin films have been deposited on (001) SrTiO3 substrates by adsorption-controlled reactive Molecular-Beam epitaxy. For a given bismuth overpressure and oxygen activity, single-phase BiFeO3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations. Four-circle x-ray diffraction reveals phase-pure, epitaxial films with ω rocking curve full width at half maximum values as narrow as 29arcsec (0.008°). Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 2.74eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO3 films.
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adsorption controlled Molecular Beam epitaxial growth of bifeo3
Applied Physics Letters, 2007Co-Authors: Jon F Ihlefeld, D G Schlom, T Heeg, Y B Chen, J Schubert, Amit Kumar, Venkatraman Gopalan, Xiaoqing Pan, P Schiffer, J OrensteinAbstract:BiFeO3 thin films have been deposited on (111) SrTiO3 single crystal substrates by reactive Molecular-Beam epitaxy in an adsorption-controlled growth regime. This is achieved by supplying a bismuth overpressure and utilizing the differential vapor pressures between bismuth oxides and BiFeO3 to control stoichiometry. Four-circle x-ray diffraction reveals phase-pure, untwinned, epitaxial, (0001)-oriented films with rocking curve full width at half maximum values as narrow as 25arcsec (0.007°). Second harmonic generation polar plots combined with diffraction establish the crystallographic point group of these untwinned epitaxial films to be 3m at room temperature.
T Tiedje - One of the best experts on this subject based on the ideXlab platform.
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growth of high bi concentration gaas1 xbix by Molecular Beam epitaxy
Applied Physics Letters, 2012Co-Authors: Ryan B Lewis, Mostafa Masnadishirazi, T TiedjeAbstract:The incorporation of Bi is investigated in the Molecular Beam epitaxy growth of GaAs1−xBix. Bi content increases rapidly as the As2:Ga flux ratio is lowered to 0.5 and then saturates for lower flux ratios. Growth under Ga and Bi rich conditions shows that Bi content increases strongly with decreasing temperature. A model is proposed where Bi from a wetting layer incorporates through attachment to Ga-terminated surface sites. The weak Ga-Bi bond can be broken thermally, ejecting Bi back into the wetting layer. Highly crystalline films with up to 22% Bi were grown at temperatures as low as 200 °C.
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Molecular Beam epitaxy growth of gaas1 xbix
Applied Physics Letters, 2003Co-Authors: S Tixier, M Adamcyk, T Tiedje, S Francoeur, A Mascarenhas, Peng Wei, F SchiettekatteAbstract:GaAs1−xBix epilayers with bismuth concentrations up to x=3.1% were grown on GaAs by Molecular Beam epitaxy. The Bi content in the films was measured by Rutherford backscattering spectroscopy. X-ray diffraction shows that GaAsBi is pseudomorphically strained to GaAs but that some structural disorder is present in the thick films. The extrapolation of the lattice constant of GaAsBi to the hypothetical zincblende GaBi alloy gives 6.33±0.06 A. Room-temperature photoluminescence of the GaAsBi epilayers is obtained and a significant redshift in the emission of GaAsBi of ∼84 meV per percent Bi is observed.
Shumin Wang - One of the best experts on this subject based on the ideXlab platform.
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Molecular Beam epitaxy growth of gasb1 xbix without rotation
Vacuum, 2019Co-Authors: Chaodan Chi, Li Yue, Yanchao Zhang, Zhenpu Zhang, Shumin WangAbstract:Abstract GaSb1-xBix thin film was grown on a 2 inch GaSb substrate by Molecular Beam epitaxy (MBE) without substrate rotation. Bi composition is found to vary from 2.76% to 3.98% across the wafer. The distribution of Bi content is mainly determined by spatial non-uniformity of Sb/Ga flux ratio, while Bi flux has slightly influence. Ostwald ripening process is confirmed to be reason for bigger Bi droplets via Bi surface diffusion. With the increase of Sb/Ga flux ratio, Ostwald ripening process is suppressed. At high Bi flux, excess Ga atoms accumulate on surface and form droplets.
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Molecular Beam epitaxy growth of alas1 x bi x
Semiconductor Science and Technology, 2019Co-Authors: Li Yue, Yanchao Zhang, Zhenpu Zhang, Chang Wang, Lijuan Wang, Hao Liang, Shumin WangAbstract:High quality AlAs1-xBix layers with Bi composition of 3%-10.5% have been successfully grown by Molecular Beam epitaxy. The Bi incorporation is confirmed by Rutherford backscattering spectroscopy. For a 400 nm thick AlAsBi layer, the strain relaxation occurs when the Bi composition is larger than 6.5%. Flux ratio is calculated from Knudsen-cell model and Maxwell equation, according to the geometrical relationship of our equipment. The Bi incorporation increases with increasing the As-Al flux ratio as well as the Bi flux. The extrapolation lattice constant of hypothetic zincblende AlBi alloy is about 6.23 angstrom.
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growth and material properties of inpbi thin films using gas source Molecular Beam epitaxy
Journal of Alloys and Compounds, 2016Co-Authors: Peng Wang, Xiaoyan Wu, Kai Wang, Liyao Zhang, Qian Gong, Shumin WangAbstract:The effects of Bi, In flux and PH3 pressure on Bi incorporation, structural and transport properties of InPBi grown by gas source Molecular Beam epitaxy have been systematically studied. Incorporation of Bi behaves like a dopant and its content increases linearly with Bi flux and inversely with the InP growth rate (In flux), and is independent of the PH3 pressure studied. High PH3 pressure causes rough surface and introduction of Bi improves surface quality. Intrinsic InP grown at a low temperature reveals n-type due to the P-ln antisite defects and the electron density is proportional to the PH3 pressure and inversely proportional to the InP growth rate. Incorporation of Bi induces p-type dopant that compensates the background electron concentration but doesn't degrade the electron mobility for the Bi content up to 2.4%. These results suggest that there is still a large room left to optimize material quality and maximize Bi incorporation in InPBi using gas source Molecular Beam epitaxy.
