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H Bracht - One of the best experts on this subject based on the ideXlab platform.
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defect interactions in sn1 xgex Random Alloys
Applied Physics Letters, 2009Co-Authors: Alexander Chroneos, Chao Jiang, R W Grimes, Udo Schwingenschlogl, H BrachtAbstract:Sn1−xGex Alloys are candidates for buffer layers to match the lattices of III-V or II-VI compounds with Si or Ge for microelectronic or optoelectronic applications. In the present work electronic structure calculations are used to study relative energies of clusters formed between Sn atoms and lattice vacancies in Ge that relate to Alloys of low Sn content. We also establish that the special quasiRandom structure approach correctly describes the Random Alloy nature of Sn1−xGex with higher Sn content. In particular, the calculated deviations of the lattice parameters from Vegard’s Law are consistent with experimental results.
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Defect interactions in Sn1−xGex Random Alloys
Applied Physics Letters, 2009Co-Authors: Alexander Chroneos, Chao Jiang, R W Grimes, Udo Schwingenschlogl, H BrachtAbstract:Sn1−xGex Alloys are candidates for buffer layers to match the lattices of III-V or II-VI compounds with Si or Ge for microelectronic or optoelectronic applications. In the present work electronic structure calculations are used to study relative energies of clusters formed between Sn atoms and lattice vacancies in Ge that relate to Alloys of low Sn content. We also establish that the special quasiRandom structure approach correctly describes the Random Alloy nature of Sn1−xGex with higher Sn content. In particular, the calculated deviations of the lattice parameters from Vegard’s Law are consistent with experimental results.
Alexander Chroneos - One of the best experts on this subject based on the ideXlab platform.
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defect interactions in sn1 xgex Random Alloys
Applied Physics Letters, 2009Co-Authors: Alexander Chroneos, Chao Jiang, R W Grimes, Udo Schwingenschlogl, H BrachtAbstract:Sn1−xGex Alloys are candidates for buffer layers to match the lattices of III-V or II-VI compounds with Si or Ge for microelectronic or optoelectronic applications. In the present work electronic structure calculations are used to study relative energies of clusters formed between Sn atoms and lattice vacancies in Ge that relate to Alloys of low Sn content. We also establish that the special quasiRandom structure approach correctly describes the Random Alloy nature of Sn1−xGex with higher Sn content. In particular, the calculated deviations of the lattice parameters from Vegard’s Law are consistent with experimental results.
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Defect interactions in Sn1−xGex Random Alloys
Applied Physics Letters, 2009Co-Authors: Alexander Chroneos, Chao Jiang, R W Grimes, Udo Schwingenschlogl, H BrachtAbstract:Sn1−xGex Alloys are candidates for buffer layers to match the lattices of III-V or II-VI compounds with Si or Ge for microelectronic or optoelectronic applications. In the present work electronic structure calculations are used to study relative energies of clusters formed between Sn atoms and lattice vacancies in Ge that relate to Alloys of low Sn content. We also establish that the special quasiRandom structure approach correctly describes the Random Alloy nature of Sn1−xGex with higher Sn content. In particular, the calculated deviations of the lattice parameters from Vegard’s Law are consistent with experimental results.
Adrian Powell - One of the best experts on this subject based on the ideXlab platform.
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formation of β sic nanocrystals by the relaxation of si1 ycy Random Alloy layers
Applied Physics Letters, 1994Co-Authors: Adrian Powell, F K Legoues, Subramanian S IyerAbstract:In this work we consider the relaxation behavior of Si1−yCy Random Alloys grown epitaxially on Si, with 0.005≳y≳0.05. The Si1−yCy layers are under tensile strain as grown and at annealing temperatures below 900 °C the relaxation of strain is achieved by dislocation formation, in a fashion similar to SiGe relaxation. However, at temperatures in excess of 900 °C the C, which at lower temperatures remained in substitutional sites, precipitates out of the lattice, this removes all of the tensile strain from the layer. The nature of this precipitation is to form single crystal, nanoparticles of β‐SiC with the same lattice orientation as the Si lattice in which they are created. These nanoparticles are of uniform diameter (3±1 nm for y=0.005 Si1−yCy material) and Randomly dispersed throughout the original Si1−yCy region. This ability to produce nanocrystals of wide band‐gap material within the Si matrix should enable the exploration of mesoscopic phenomena. The nanoparticles once formed also block the movement ...
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stability of strained si1 ycy Random Alloy layers
Journal of Vacuum Science & Technology B, 1993Co-Authors: Adrian Powell, K. Eberl, F. E. Legoues, S.s. IyerAbstract:Si1−yCy Random Alloy material opens up new opportunities for heterostructures based on Si. It offers the possibility of tensile strain within the Si material system without the requirement for relaxed Si1−xGex buffer layers, and when combined with the Si1−xGex system allows some degree of independence between strain and band gap in Si‐based semiconductors. Unlike the Si1−xGex system, the Si1−yCy system has a high misfit (52%) and low solubility (<10−6), with a propensity for compound formation. In order to prevent carbide formation, the structures are kinetically stabilized by low‐temperature growth. In this work, we consider the metastable critical thickness that can be reached by the Si1−yCy Alloys and find it to be considerably less than the comparable thicknesses obtained from Si1−xGex Alloys on Si. In the Si1−yCy system, we have found two distinct relaxation regimes for the strained layers. These being low and high mismatch regions where relaxation occurs by the creation of 60° dislocations and micro...
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Stability of strained Si1−yCy Random Alloy layers
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1993Co-Authors: Adrian Powell, K. Eberl, F. E. Legoues, S.s. IyerAbstract:Si1−yCy Random Alloy material opens up new opportunities for heterostructures based on Si. It offers the possibility of tensile strain within the Si material system without the requirement for relaxed Si1−xGex buffer layers, and when combined with the Si1−xGex system allows some degree of independence between strain and band gap in Si‐based semiconductors. Unlike the Si1−xGex system, the Si1−yCy system has a high misfit (52%) and low solubility (
Subramanian S Iyer - One of the best experts on this subject based on the ideXlab platform.
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formation of β sic nanocrystals by the relaxation of si1 ycy Random Alloy layers
Applied Physics Letters, 1994Co-Authors: Adrian Powell, F K Legoues, Subramanian S IyerAbstract:In this work we consider the relaxation behavior of Si1−yCy Random Alloys grown epitaxially on Si, with 0.005≳y≳0.05. The Si1−yCy layers are under tensile strain as grown and at annealing temperatures below 900 °C the relaxation of strain is achieved by dislocation formation, in a fashion similar to SiGe relaxation. However, at temperatures in excess of 900 °C the C, which at lower temperatures remained in substitutional sites, precipitates out of the lattice, this removes all of the tensile strain from the layer. The nature of this precipitation is to form single crystal, nanoparticles of β‐SiC with the same lattice orientation as the Si lattice in which they are created. These nanoparticles are of uniform diameter (3±1 nm for y=0.005 Si1−yCy material) and Randomly dispersed throughout the original Si1−yCy region. This ability to produce nanocrystals of wide band‐gap material within the Si matrix should enable the exploration of mesoscopic phenomena. The nanoparticles once formed also block the movement ...
E P Oreilly - One of the best experts on this subject based on the ideXlab platform.
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impact of Random Alloy fluctuations on inter well transport in ingan gan multi quantum well systems an atomistic non equilibrium green s function study
Journal of Physics: Condensed Matter, 2021Co-Authors: Michael Odonovan, Mathieu Luisier, E P Oreilly, Stefan SchulzAbstract:Recent experimental studies indicate the presence of ballistic hole transport in InGaN multi quantum well structures. Widely used drift-diffusion models cannot give insight into this question, since quantum mechanical effects, such as tunneling, are not included in such semi-classical approaches. Also atomistic effects, e.g. carrier localization effects and built-in field variations due to (Random) Alloy fluctuations, are often neglected in ballistic transport calculations on InGaN quantum well systems. In this work we use atomistic tight-binding theory in conjunction with a non-equilibrium Green's function approach to study electron and hole ballistic transport in InGaN multi quantum well systems. Our results show that for electrons the Alloy microstructure is of secondary importance for their ballistic transport properties, while for hole transport the situation is different. We observe for narrow barrier widths in an InGaN multi quantum well system that (Random) Alloy fluctuations give rise to extra hole transmission channels when compared to a virtual crystal description of the same system. We attribute this effect to the situation that in the Random Alloy case,k∥-vector conservation is broken/relaxed and therefore the ballistic hole transport is increased. However, for wider barrier width this effect is strongly reduced, which is consistent with recent experimental studies. Our findings also provide a possible explanation for recent experimental results where Alloying the barrier between the wells leads to enhanced ballistic (hole) transport in InGaN multi quantum well systems.
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theoretical analysis of influence of Random Alloy fluctuations on the optoelectronic properties of site controlled 111 oriented ingaas gaas quantum dots
Physical Review B, 2016Co-Authors: R Benchamekh, Stefan Schulz, E P OreillyAbstract:We use an $s{p}^{3}{d}^{5}{s}^{*}$ tight-binding model to investigate the electronic and optical properties of realistic site-controlled (111)-oriented InGaAs/GaAs quantum dots. Special attention is paid to the impact of Random Alloy fluctuations on several factors that determine the fine-structure splitting in these systems. Using a pure InAs/GaAs quantum dot as a reference system, we show that the combination of spin-orbit coupling and biaxial strain effects can lead to sizable spin-splitting effects in these systems. Then, a realistic Alloyed InGaAs/GaAs quantum dot with 25% InAs content is studied. Our analysis reveals that the impact of Random Alloy fluctuations on the electronic and optical properties of (111)-oriented InGaAs/GaAs quantum dots reduces strongly as the lateral size of the dot increases and approaches realistic sizes. For instance the optical matrix element shows an almost vanishing anisotropy in the (111)-growth plane. Furthermore, conduction and valence band mixing effects in the system under consideration are strongly reduced compared to standard (100)-oriented InGaAs/GaAs systems. All these factors indicate a reduced fine-structure splitting in site-controlled (111)-oriented InGaAs/GaAs quantum dots. Thus, we conclude that quantum dots with realistic (50\char21{}80 nm) base length represent promising candidates for polarization-entangled-photon generation, consistent with recent experimental data.
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Random Alloy fluctuations and structural inhomogeneities in c plane inxga1 xn quantum wells theory of ground and excited electron and hole states
RSC Advances, 2016Co-Authors: Daniel S P Tanner, E P Oreilly, Miguel A Caro, Stefan SchulzAbstract:We present a detailed theoretical analysis of the electronic structure of c-plane InGaN/GaN quantum wells with indium contents varying between 10% and 25%. The electronic structure of the quantum wells is treated by means of an atomistic tight-binding model, accounting for variations in strain and built-in field due to Random Alloy fluctuations. Our analysis reveals strong localisation effects in the hole states. These effects are found not only in the ground states, but also the excited states. We conclude that localisation effects persist to of order 100 meV into the valence band, for as little as 10% indium in the quantum well, giving rise to a significant density of localised states. We find, from an examination of the modulus overlap of the wave functions, that the hole states can be divided into three regimes of localisation. Our results also show that localisation effects due to Random Alloy fluctuations are far less pronounced for electron states. However, the combination of electrostatic built-in field, Alloy fluctuations and structural inhomogeneities, such as well-width fluctuations, can nevertheless lead to significant localisation effects in the electron states, especially at higher indium contents. Overall, our results are indicative of individually localised electron and hole states, consistent with the experimentally proposed explanation of time-dependent photoluminescence results in c-plane InGaN/GaN QWs.
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Random Alloy fluctuations and structural inhomogeneities in c plane in _ x ga _ 1 x n quantum wells theory of ground and excited electron and hole states
arXiv: Materials Science, 2016Co-Authors: Daniel S P Tanner, E P Oreilly, Miguel A Caro, Stefan SchulzAbstract:We present a detailed theoretical analysis of the electronic structure of $c$-plane InGaN/GaN quantum wells with indium contents varying between 10\% and 25\%. The electronic structure of the quantum wells is treated by means of an atomistic tight-binding model, accounting for variations in strain and built-in field due to Random Alloy fluctuations. Our analysis reveals strong localisation effects in the hole states. These effects are found not only in the ground states, but also the excited states. We conclude that localisation effects persist to of order 100~meV into the valence band, for as little as 10\% indium in the quantum well, giving rise to a significant density of localised states. We find, from an examination of the modulus overlap of the wave functions, that the hole states can be divided into three regimes of localisation. Our results also show that localisation effects due to Random Alloy fluctuations are far less pronounced for electron states. However, the combination of electrostatic built-in field, Alloy fluctuations and structural inhomogeneities, such as well-width fluctuations, can nevertheless lead to significant localisation effects in the electron states, especially at higher indium contents. Overall, our results are indicative of individually localised electron and hole states, consistent with the experimentally proposed explanation of time-dependent photoluminescence results in $c$-plane InGaN/GaN QWs.
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atomistic analysis of the electronic structure of m plane ingan gan quantum wells carrier localization effects in ground and excited states due to Random Alloy fluctuations
Physica Status Solidi B-basic Solid State Physics, 2016Co-Authors: Daniel S P Tanner, E P Oreilly, Miguel A Caro, Stefan SchulzAbstract:We present a detailed atomistic analysis of the electronic properties of m-plane InGaN/GaN quantum wells. The tight-binding model used treats realistically sized systems atomistically and accounts for compositional and structural inhomogeneities. Local variation in strain and built-in potential arising from Random Alloy fluctuations are explicitly included in the model. Many energy states of the supercells considered are calculated in order to determine the impact of the Alloy fluctuations on the electronic structure of the system under investigation. We find that while the electrons are relatively insensitive to the local indium environment, the hole states are highly sensitive to it and are subject to very strong localization effects. These effects persist several states into the valence band. This strong localization of the hole states leads to a very broad distribution of ground state energies in different Random configurations. Furthermore, we see that the localization leads to poor overlap between different hole states resulting in a reduced probability of transfer of carriers between different states. This feature should play an important role for transport properties in m-plane InGaN/GaN QWs.
