@article{khafagy_hatem_bedair_2021, title={Thermodynamics Models for V-pit Nucleation and Growth in III-Nitride on Silicon}, volume={73}, ISSN={["1543-1851"]}, DOI={10.1007/s11837-020-04421-z}, number={1}, journal={JOM}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2021}, month={Jan}, pages={293–298} }
 @article{khafagy_hatem_bedair_2020, title={Dislocation-Based Thermodynamic Models of V-Pits Formation and Strain Relaxation in InGaN/GaN Epilayers on Si Substrates}, ISBN={["978-3-030-36295-9"]}, ISSN={["2367-1696"]}, DOI={10.1007/978-3-030-36296-6_188}, abstractNote={The strain relaxation mechanism in III-N materials is occurred through the motion of dislocationsDislocations that generated at III-N/Si interfaceInterface as a result of large mismatch in lattice and thermal expansion coefficients. As a result of the large lattice mismatch between different layers, the upper layer gets strained and with thicker layers, the strain energy increases until a thickness limit called the critical material thickness. Most of such dislocationsDislocations (threading dislocationsThreading dislocations ) penetrate the top surface forming V-pits defectsV-pits Defects at the top surface that relax the material. These V-pits directly affect the device efficiency, performance, and reliability. Therefore, in this paper, a thermodynamics-based model will be used to study the V-pits formulation and growth in the III-N (especially, InGaN-based materials). In this model, three types of energies are used under a balanced system to model the V-pit formation and growth. These energies are the strain energy in the InGaN epilayer, the destruction energy as a result of dislocation to form the V-pit, and the strain energy of the V-pits facets that generated during the facet nucleationNucleation .}, journal={TMS 2020 149TH ANNUAL MEETING & EXHIBITION SUPPLEMENTAL PROCEEDINGS}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2020}, pages={2057–2064} }
 @article{khafagy_hatem_bedair_2019, title={Modelling of III-Nitride Epitaxial Layers Grown on Silicon Substrates with Low Dislocation-Densities}, volume={4}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2019.49}, abstractNote={Large lattice and thermal expansion coefficients mismatches between III-Nitride ( III N ) epitaxial layers and their substrates inevitably generate defects on the interfaces. Such defects as dislocations affect the reliability, life time, and performance of photovoltaic (PV) devices. High dislocation densities in epitaxial layer generate higher v-shaped pits densities on the layer top surface that also directly affect the device performance. Therefore, using an approach such as the embedded void approach (EVA) for defects reduction in the epitaxial layers is essential. EVA relies on the generation of high densities of embedded microvoids (~10^8/cm^2), with ellipsoidal shapes. These tremendous number of microvoids are etched near the interface between the III N thin-film and its substrate where the dislocation densities present with higher values. This article used a 3-D constitutive model that accounts the crystal plasticity formulas and specialized finite element (FE) formulas to model the EVA in multi-junction PV and therefore to study the effect of the embedded void approach on the defects reduction. Mesh convergence and 2-D analytical solution validation is conducted with accounting thermal stresses. Several aspect and volume ratios of the embedded microvoids are used to optimize the microvoid dimensions.}, number={13}, journal={MRS ADVANCES}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2019}, pages={755–760} }
 @article{khafagy_hatem_bedair_2018, title={Three-Dimensional Crystal-Plasticity Based Model for Intrinsic Stresses in Multi-junction Photovoltaic}, ISBN={["978-3-319-72361-7"]}, ISSN={["2367-1181"]}, DOI={10.1007/978-3-319-72362-4_41}, abstractNote={Our understanding for intrinsic stresses and defects evolution in photovoltaic devices has became an essential part of new developments. In particular, Multi-Junction Photovoltaic (MJ-PV) modules depend on multi-layer structures that may suffer high dislocation-densities as a result of high lattice and thermal expansion coefficient mismatch. These defects limit the performance, reliability, and lifetime of PV devices. In the current study, a three-dimensional multiple-slip crystal-plasticity model and specialized finite-element formulations are used to investigate InGaN growth on Si substrates. The formulation is based on accounting for thermal and intrinsic stresses as a result of different processing conditions and microstructures. Furthermore, the formulation was used to investigate a recently developed technique, Embedded Void Approach (EVA), which can be used to address both the high density of defects and the cracking/bowing of InGaN growth on Si. The current work lays the groundwork for more extensive use of silicon in MJ-PV devices.}, journal={ENERGY TECHNOLOGY 2018: CARBON DIOXIDE MANAGEMENT AND OTHER TECHNOLOGIES}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2018}, pages={453–461} }