The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Robert Hull - One of the best experts on this subject based on the ideXlab platform.
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Misfit dislocation propagation kinetics in GexSi1−x/Ge(100) heterostructures
Applied Physics Letters, 1994Co-Authors: Robert Hull, John C. Bean, B. E. Weir, L. J. Peticolas, K. Prabhakaran, Toshio OginoAbstract:We report measurements of misfit dislocation propagation velocities in GexSi1−x epilayers grown upon Ge(100) substrates, as opposed to the more usual Si(100) substrates. This geometry allows us to study structures with high Ge concentration (x≥0.8), and to compare with previous extensive measurements for lower Ge concentration layers (x≤0.35) grown upon Si(100). It is found that all data are well described by a misfit dislocation velocity which is linear with Excess Stress, and which incorporates a compositionally dependent activation energy with linear interpolation between bulk values for Si and Ge. The combined data sets from structures grown on Si(100) and Ge(100) substrates is analyzed in the framework of the diffusive double kink model for dislocation motion.
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Misfit dislocation microstructure and kinetics for InxGa1−xAs/InP(100) and (110) interfaces under tensile and compressive Stress
Applied Physics Letters, 1993Co-Authors: Robert Hull, R. A. Logan, B. E. Weir, J. M. VandenbergAbstract:Misfit dislocation microstructures and strain relaxation kinetics are studied for 1% lattice mismatched (100) and (110) interfaces under tensile and compressive Stress in the InxGa1−xAs/InP system. Misfit dislocations are observed to be either 60° a/2〈101〉 total [for (100) compressive and (110) tensile configurations] or 90° a/6〈112〉 partial [dominant for (100) tensile and (110) compressive configurations] types. Relaxation kinetics are observed to be substantially faster for 90° a/6〈112〉 than 60° a/2〈101〉 dislocations. This produces significantly different relaxation rates for (100) versus (110) interfaces and compressive versus tensile Stress. The relaxation is also found to be an extremely strong function of Excess Stress, with an increase of about two orders of magnitude of dislocation density per 100 MPa increase in Excess Stress for interfacial dislocation densities in the range 102–106 cm−1.
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Quantitative analysis of strain relaxation in GexSi1−x/Si(110) heterostructures and an accurate determination of stacking fault energy in GexSi1−x alloys
Applied Physics Letters, 1992Co-Authors: Robert Hull, John C. Bean, B. E. Weir, L. J. Peticolas, D. Bahnck, Leonard C. FeldmanAbstract:We report a quantitative theoretical and experimental analysis of strain relaxation in GexSi1−x/Si(110) heterostructures. It is shown that above a critical composition, the critical thickness for edge a/6〈112〉 Shockley partial dislocations is less than that for 60° a/2〈110〉 total dislocations. The net (Excess) Stress is greater on the edge a/6〈112〉 dislocations for epilayer thicknesses, h
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On the Dodson–Tsao Excess Stress for glide of a threading dislocation in a strained epitaxial layer
Journal of Applied Physics, 1992Co-Authors: L. B. Freund, Robert HullAbstract:The concept of Excess Stress was originally introduced in a study of elastic strain relaxation in an epitaxial layer grown beyond its critical thickness, where it was proposed as the relevant Stress in a kinetic law for dislocation motion. The concept has subsequently been applied in a variety of studies of strain relaxation, but without a standard definition as a basis for quantitative comparisons. The purpose here is to propose a fundamental definition of Excess Stress as the particular Stress measure which is work‐conjugate to the Burgers displacement during glide of a threading dislocation in a strained layer. This definition also has the feature of being consistent with definitions of effective Stress in kinetic laws of glide in bulk materials.
Shiyong Liu - One of the best experts on this subject based on the ideXlab platform.
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Effect of non-strained capping layer on Excess Stress in strained layers
Science China-mathematics, 1999Co-Authors: Zhi Jin, Shuren Yang, Benzhong Wang, Shiyong LiuAbstract:The effects of the capping-layer thickness and the discrepancy of the numbers of misfit dislocations at the upper and lower interfaces in capped layer on the Excess Stress are considered. Based on this, the formulae of Excess Stresses for single-and double-kink models are modified and a new formula is derived, which unifies single- and doublekink models and is valid for arbitrary capping-layer thickness. It is useful to complete the description of the formation and motion of misfit dislocations in strained layers.
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A new expression of Excess Stress and the stability of buried strained heterostructures
Solid-State Electronics, 1999Co-Authors: Zhi Jin, Shuren Yang, Shiyong LiuAbstract:Abstract A new mechanism of strain relaxation in buried strained layers is proposed. According to this mechanism, the mixture of single and paired misfit dislocations appears to relax the misfit strain. The corresponding formula of Excess force and Stresses is derived. In this formula, the free-surface boundary condition, the interaction and distribution of misfit dislocations are all incorporated. The formula can be applied to arbitrary strained heterostructures. Both single- and double-kink models are some extreme condition of our formula. A formula of the critical thickness of the strained layer is derived.
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The effects of misfit dislocation distribution and capping layer on Excess Stress
Applied Physics Letters, 1999Co-Authors: Zhi Jin, Shuren Yang, Benzhong Wang, Shiyong LiuAbstract:It is generally accepted that in the buried strained-layer structure, the strain is relaxed by paired misfit dislocations: one at the upper interface and the other at the lower interface. But, experimentally it is not so. In this letter, the effect of a mixture of single and paired misfit dislocations is incorporated in the formula of Excess force. In this formula, the effects of the capping layer with arbitrary thickness and the interaction of misfit dislocations at different interfaces are also included. Based on the formula, the Excess Stresses are derived. These formulas can be used to predict the Excess Stress of strained layers with arbitrary heterostructure structures. They also can describe the transition process from the single-kink to the double-kink mechanism.
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Stability of strained MQWs in laser structure
Semiconductor Lasers III, 1998Co-Authors: Zhi Jin, Shuren Yang, Benzhong Wang, Shiyong LiuAbstract:In this paper, the stability of strained MQWs in laser structure is discussed. The Excess Stress is the driving force of misfit dislocation multiplication and is a very important factor of strained MQWs stability. So we calculate the Excess Stress using the single-kink model. Our results show that the maximum position of Excess Stress is related to the barrier and well thicknesses and mismatches in the well(s). The lattice-matched barriers can dilute the Excess Stress. The capping layer can also dilute the Excess Stress in a certain degree. We then calculate the strain relaxation using the dynamic model of dislocations. In this model, the strain relaxation is driven by the Excess strains. In this paper, the criteria of the stability of MQWs in laser structure is that the density of dislocations (or the strain relaxation) is less than a certain value. In this way, the barriers and capping layer are both important factors of MQWs stability. The method can be used to better the MQWs in laser structure.
David J. Larson - One of the best experts on this subject based on the ideXlab platform.
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Finite Element Analysis of Thermal and Stress Fields During Directional Solidification of Cadmium Telluride
Computational Mechanics ’95, 1995Co-Authors: Taipao Lee, J.c. Moosbrugger, Frederick M. Carlson, David J. LarsonAbstract:The thermal field and resulting thermoelastic Stress field were simulated for the vertical Bridgman growth of Cadmium Telluride (CdTe) crystals. The calculated temperature distribution agrees well with the data taken from the experiment. The computed Excess Stress distribution based on the calculated temperature field in the solid also agrees qualitatively with synchrotron contour topography on a slice taken from the growth ingot.
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Producibility improvements suggested by a validated process model of seeded CdZnTe vertical Bridgman growth
Producibility of II-VI Materials and Devices, 1994Co-Authors: David J. Larson, Taipao Lee, Frederick M. Carlson, Louis G. Casagrande, Don Di Marzio, Alan Levy, David R. Black, Michael DudleyAbstract:We have successfully validated theoretical models of seeded vertical Bridgman-Stockbarger CdZnTe crystal growth and post-solidification processing, using in-situ thermal monitoring and innovative material characterization techniques. The models predict the thermal gradients, interface shape, fluid flow and solute redistribution during solidification, as well as the distributions of accumulated Excess Stress that causes defect generation and redistribution. Data from the furnace and ampoule wall have validated predictions from the thermal model. Results are compared to predictions of the thermal and thermo-solutal models. We explain the measured initial, change-of-rate, and terminal compositional transients as well as the macrosegregation. Macro and micro-defect distributions have been imaged on CdZnTe wafers from 40 mm diameter boules. Superposition of topographic defect images and predicted Excess Stress patterns suggests the origin of some frequently encountered defects, particularly on a macro scale, to result from the applied and accumulated Stress fields and the anisotropic nature of the CdZnTe crystal. Implications of these findings with respect to producibility are discussed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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The Role of Thermal Stress In Vertical Bridgman Growth of CdZnTe Crystals
Materials Processing in High Gravity, 1994Co-Authors: Taipao Lee, J.c. Moosbrugger, Frederick M. Carlson, David J. LarsonAbstract:Computational studies of thermal fields and resulting thermoelastic Stress fields were undertaken for the vertical Bridgman-Stockbarger growth of CdZnTe crystals. Companion experimental studies included the growth of crystals grown with the same process parameters and the same geometry as the process modeled in the computations. Characteristics of the crystals grown were compared with the computational predictions. Predictions of growth ampoule outer wall temperatures agree well with thermocouple data taken during the growth experiment. Additionally, the computed Excess Stress distribution resulting from the thermoelastic Stress history in the solid is seen to agree qualitatively with synchrotron contour topography on a slice taken from the grown ingot. The computational models are shown to provide a good tool for the study of the influence of process parameters on the quality of crystals grown by this method, at least as far as thermal Stress influences the defect distribution. The influence of low-g and high-g environments on growth is discussed.
Zhi Jin - One of the best experts on this subject based on the ideXlab platform.
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Effect of non-strained capping layer on Excess Stress in strained layers
Science China-mathematics, 1999Co-Authors: Zhi Jin, Shuren Yang, Benzhong Wang, Shiyong LiuAbstract:The effects of the capping-layer thickness and the discrepancy of the numbers of misfit dislocations at the upper and lower interfaces in capped layer on the Excess Stress are considered. Based on this, the formulae of Excess Stresses for single-and double-kink models are modified and a new formula is derived, which unifies single- and doublekink models and is valid for arbitrary capping-layer thickness. It is useful to complete the description of the formation and motion of misfit dislocations in strained layers.
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A new expression of Excess Stress and the stability of buried strained heterostructures
Solid-State Electronics, 1999Co-Authors: Zhi Jin, Shuren Yang, Shiyong LiuAbstract:Abstract A new mechanism of strain relaxation in buried strained layers is proposed. According to this mechanism, the mixture of single and paired misfit dislocations appears to relax the misfit strain. The corresponding formula of Excess force and Stresses is derived. In this formula, the free-surface boundary condition, the interaction and distribution of misfit dislocations are all incorporated. The formula can be applied to arbitrary strained heterostructures. Both single- and double-kink models are some extreme condition of our formula. A formula of the critical thickness of the strained layer is derived.
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The effects of misfit dislocation distribution and capping layer on Excess Stress
Applied Physics Letters, 1999Co-Authors: Zhi Jin, Shuren Yang, Benzhong Wang, Shiyong LiuAbstract:It is generally accepted that in the buried strained-layer structure, the strain is relaxed by paired misfit dislocations: one at the upper interface and the other at the lower interface. But, experimentally it is not so. In this letter, the effect of a mixture of single and paired misfit dislocations is incorporated in the formula of Excess force. In this formula, the effects of the capping layer with arbitrary thickness and the interaction of misfit dislocations at different interfaces are also included. Based on the formula, the Excess Stresses are derived. These formulas can be used to predict the Excess Stress of strained layers with arbitrary heterostructure structures. They also can describe the transition process from the single-kink to the double-kink mechanism.
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Stability of strained MQWs in laser structure
Semiconductor Lasers III, 1998Co-Authors: Zhi Jin, Shuren Yang, Benzhong Wang, Shiyong LiuAbstract:In this paper, the stability of strained MQWs in laser structure is discussed. The Excess Stress is the driving force of misfit dislocation multiplication and is a very important factor of strained MQWs stability. So we calculate the Excess Stress using the single-kink model. Our results show that the maximum position of Excess Stress is related to the barrier and well thicknesses and mismatches in the well(s). The lattice-matched barriers can dilute the Excess Stress. The capping layer can also dilute the Excess Stress in a certain degree. We then calculate the strain relaxation using the dynamic model of dislocations. In this model, the strain relaxation is driven by the Excess strains. In this paper, the criteria of the stability of MQWs in laser structure is that the density of dislocations (or the strain relaxation) is less than a certain value. In this way, the barriers and capping layer are both important factors of MQWs stability. The method can be used to better the MQWs in laser structure.
Taipao Lee - One of the best experts on this subject based on the ideXlab platform.
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Finite Element Analysis of Thermal and Stress Fields During Directional Solidification of Cadmium Telluride
Computational Mechanics ’95, 1995Co-Authors: Taipao Lee, J.c. Moosbrugger, Frederick M. Carlson, David J. LarsonAbstract:The thermal field and resulting thermoelastic Stress field were simulated for the vertical Bridgman growth of Cadmium Telluride (CdTe) crystals. The calculated temperature distribution agrees well with the data taken from the experiment. The computed Excess Stress distribution based on the calculated temperature field in the solid also agrees qualitatively with synchrotron contour topography on a slice taken from the growth ingot.
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Producibility improvements suggested by a validated process model of seeded CdZnTe vertical Bridgman growth
Producibility of II-VI Materials and Devices, 1994Co-Authors: David J. Larson, Taipao Lee, Frederick M. Carlson, Louis G. Casagrande, Don Di Marzio, Alan Levy, David R. Black, Michael DudleyAbstract:We have successfully validated theoretical models of seeded vertical Bridgman-Stockbarger CdZnTe crystal growth and post-solidification processing, using in-situ thermal monitoring and innovative material characterization techniques. The models predict the thermal gradients, interface shape, fluid flow and solute redistribution during solidification, as well as the distributions of accumulated Excess Stress that causes defect generation and redistribution. Data from the furnace and ampoule wall have validated predictions from the thermal model. Results are compared to predictions of the thermal and thermo-solutal models. We explain the measured initial, change-of-rate, and terminal compositional transients as well as the macrosegregation. Macro and micro-defect distributions have been imaged on CdZnTe wafers from 40 mm diameter boules. Superposition of topographic defect images and predicted Excess Stress patterns suggests the origin of some frequently encountered defects, particularly on a macro scale, to result from the applied and accumulated Stress fields and the anisotropic nature of the CdZnTe crystal. Implications of these findings with respect to producibility are discussed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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The Role of Thermal Stress In Vertical Bridgman Growth of CdZnTe Crystals
Materials Processing in High Gravity, 1994Co-Authors: Taipao Lee, J.c. Moosbrugger, Frederick M. Carlson, David J. LarsonAbstract:Computational studies of thermal fields and resulting thermoelastic Stress fields were undertaken for the vertical Bridgman-Stockbarger growth of CdZnTe crystals. Companion experimental studies included the growth of crystals grown with the same process parameters and the same geometry as the process modeled in the computations. Characteristics of the crystals grown were compared with the computational predictions. Predictions of growth ampoule outer wall temperatures agree well with thermocouple data taken during the growth experiment. Additionally, the computed Excess Stress distribution resulting from the thermoelastic Stress history in the solid is seen to agree qualitatively with synchrotron contour topography on a slice taken from the grown ingot. The computational models are shown to provide a good tool for the study of the influence of process parameters on the quality of crystals grown by this method, at least as far as thermal Stress influences the defect distribution. The influence of low-g and high-g environments on growth is discussed.
