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- ItemEvolution of planar defects during homoepitaxial growth of β-Ga2O3 layers on (100) substrates—A quantitative model(Melville, NY : American Inst. of Physics, 2016) Schewski, R.; Baldini, M.; Irmscher, K.; Fiedler, A.; Markurt, T.; Neuschulz, B.; Remmele, T.; Schulz, T.; Wagner, G.; Galazka, Z.; Albrecht, M.We study the homoepitaxial growth of β-Ga2O3 (100) grown by metal-organic vapour phase as dependent on miscut-angle vs. the c direction. Atomic force microscopy of layers grown on substrates with miscut-angles smaller than 2° reveals the growth proceeding through nucleation and growth of two-dimensional islands. With increasing miscut-angle, step meandering and finally step flow growth take place. While step-flow growth results in layers with high crystalline perfection, independent nucleation of two-dimensional islands causes double positioning on the (100) plane, resulting in twin lamellae and stacking mismatch boundaries. Applying nucleation theory in the mean field approach for vicinal surfaces, we can fit experimentally found values for the density of twin lamellae in epitaxial layers as dependent on the miscut-angle. The model yields a diffusion coefficient for Ga adatoms of D = 7 × 10−9 cm2 s−1 at a growth temperature of 850 °C, two orders of magnitude lower than the values published for GaAs.
- ItemEngineering the semiconductor/oxide interaction for stacking twin suppression in single crystalline epitaxial silicon(111)/insulator/Si(111) heterostructures(College Park, MD : Institute of Physics Publishing, 2008) Schroetter, T.; Zaumseil, P.; Seifarth, O.; Giussani, A.; Müssig, H.-J.; Storck, P.; Geiger, D.; Lichte, H.; Dabrowski, J.The integration of alternative semiconductor layers on the Si material platform via oxide heterostructures is of interest to increase the performance and/or functionality of future Si-based integrated circuits. The single crystalline quality of epitaxial (epi) semiconductor-insulator-Si heterostructures is however limited by too high defect densities, mainly due to a lack of knowledge about the fundamental physics of the heteroepitaxy mechanisms at work. To shed light on the physics of stacking twin formation as one of the major defect mechanisms in (111)-oriented fcc-related heterostructures on Si(111), we report a detailed experimental and theoretical study on the structure and defect properties of epi-Si(111)/Y2O 3/Pr2O3/Si(111) heterostructures. Synchrotron radiation-grazing incidence x-ray diffraction (SR-GIXRD) proves that the engineered Y2O3/Pr2O3 buffer dielectric heterostructure on Si(111) allows control of the stacking sequence of the overgrowing single crystalline epi-Si(111) layers. The epitaxy relationship of the epi-Si(111)/insulator/Si(111) heterostructure is characterized by a type A/B/A stacking configuration. Theoretical ab initio calculations show that this stacking sequence control of the heterostructure is mainly achieved by electrostatic interaction effects across the ionic oxide/covalent Si interface (IF). Transmission electron microscopy (TEM) studies detect only a small population of misaligned type B epi-Si(111) stacking twins whose location is limited to the oxide/epiSi IF region. Engineering the oxide/semiconductor IF physics by using tailored oxide systems opens thus a promising approach to grow heterostructures with well-controlled properties. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
- ItemA novel engineered oxide buffer approach for fully lattice-matched SOI heterostructures(College Park, MD : Institute of Physics Publishing, 2010) Giussani, A.; Zaumseil, P.; Seifarth, O.; Storck, P.; Schroeder, T.Epitaxial (epi) oxides on silicon can be used to integrate novel device concepts on the canonical Si platform, including functional oxides, e.g. multiferroics, as well as alternative semiconductor approaches. For all these applications, the quality of the oxide heterostructure is a key figure of merit. In this paper, it is shown that, by co-evaporating Y2O3 and Pr2O3 powder materials, perfectly lattice-matched PrYO3(111) epilayers with bixbyite structure can be grown on Si(111) substrates. A high-resolution x-ray diffraction analysis demonstrates that the mixed oxide epi-films are single crystalline and type B oriented. Si epitaxial overgrowth of the PrYO3(111)/Si(111) support system results in flat, continuous and fully lattice-matched epi-Si(111)/PrYO3(111)/Si(111) silicon-on-insulator heterostructures. Raman spectroscopy proves the strain-free nature of the epi-Si films. A Williamson-Hall analysis of the mixed oxide layer highlights the existence of structural defects in the buffer, which can be explained by the thermal expansion coefficients of Si and PrYO3. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
- ItemEpitaxial growth and stress relaxation of vapor-deposited Fe-Pd magnetic shape memory films(College Park, MD : Institute of Physics Publishing, 2009) Kühnemund, L.; Edler, T.; Kock, I.; Seibt, M.; Mayr, S.G.To achieve maximum performance in microscale magnetic shape memory actuation devices epitaxial films several hundred nanometers thick are needed. Epitaxial films were grown on hot MgO substrates (500 °C and above) by e-beam evaporation. Structural properties and stress relaxation mechanisms were investigated by high-resolution transmission electron microscopy, in situ substrate curvature measurements and classical molecular dynamics (MD) simulations. The high misfit stress incorporated during Vollmer-Weber growth at the beginning was relaxed by partial or perfect dislocations depending on the substrate temperature. This relaxation allowed the avoidance of a stressinduced breakdown of epitaxy and no thickness limit for epitaxy was found. For substrate temperatures of 690 °C or above, the films grew in the fee austenite phase. Below this temperature, iron precipitates were formed. MD simulations showed how these precipitates influence the movements of partial dislocations, and can thereby explain the higher stress level observed in the experiments in the initial stage of growth for these films. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
- ItemMechanisms of stress generation and relaxation during pulsed laser deposition of epitaxial Fe-Pd magnetic shape memory alloy films on MgO(Milton Park : Taylor & Francis, 2008) Edler, Tobias; Buschbeck, Jörg; Mickel, Christine; Fähler, Sebastian; Mayr, S.G.Mechanical stress generation during epitaxial growth of Fe–Pd thin films on MgO from pulsed laser deposition is a key parameter for the suitability in shape memory applications. By employing in situ substrate curvature measurements, we determine the stress states as a function of film thickness and composition. Depending on composition, different stress states are observed during initial film growth, which can be attributed to different misfits. Compressive stress generation by atomic peening is observed in the later stages of growth. Comparison with ex situ x-ray based strain measurements allows integral and local stress to be distinguished and yields heterogeneities of the stress state between coherent and incoherent regions. In combination with cross-sectional TEM measurements the relevant stress relaxation mechanism is identified to be stress-induced martensite formation with (111) twinning.