Fundamental study of nucleation and heteroepitaxial thin film growth using ionized source beam
Yoo, Myung Cheol
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https://hdl.handle.net/2142/20415
Description
Title
Fundamental study of nucleation and heteroepitaxial thin film growth using ionized source beam
Author(s)
Yoo, Myung Cheol
Issue Date
1992
Doctoral Committee Chair(s)
Kim, Kyekyoon
Department of Study
Materials Science and Engineering
Discipline
Materials Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Engineering, Metallurgy
Engineering, Materials Science
Language
eng
Abstract
Ni clusters have been produced using a nozzle source beam. The adiabatically expanded Ni clusters were impact-ionized, accelerated and delivered to carbon substrate for the control of size and distribution. The deposition parameters investigated are the diameter of the adiabatic nozzle, the proportion and energy of the ionized particles in the cluster beam, the substrate temperature, and the deposition time. The use of electron irradiation and acceleration of the source beam has proven to be particularly effective in producing uniform Ni clusters as small as 10A with very narrow size distribution. An Arrhenius plot of substrate temperature versus average cluster diameter revealed that the activation energy due to the beam ionization was 2.5 times higher than the neutral nozzle beam case. Also, the resulting critical shear stress acting on the interface between the cluster and the substrate showed that the critical shear stress of ionized clusters was one order of magnitude higher than that of neutral clusters. These results indicate that the two dimensional cluster growth would be favored by the enhanced coalescence if the neutral clusters are ionized during deposition.
Anti-phase-domain-free, layer-by-layer growth of epitaxial GaAs thin films on exactly oriented silicon(100) has been achieved by As beam ionization and acceleration. To understand the differences in defect formation and initial nucleation, a GaAs film grown with ionized As source beam was compared with that of conventional neutral source beam. Compared to the very irregular surface and low x-ray diffraction intensity of the GaAs films grown with neutral source beam, very flat surface and higher crystal quality of epitaxial GaAs thin films was obtained by ionization and acceleration of As source beam. The results of defect characterization using cross-section TEM showed that no APD's were observable in the GaAs epilayer grown with ionized source beam epitaxy (ISBE) and the nature of the dislocations and stacking faults in the GaAs epilayer was quite different between the two cases. These evidences strongly suggest that the ionization and acceleration of As source beam not only enhance the As adatom mobility, but also stimulate the Ga adatom to prevent aggregation of Ga atoms to form 3-D islands during early stage of thin film growth. As a result, these combined effects would promote the coalescence process, thus controlling the nucleation characteristics from three-dimensional growth to layer-by-layer growth in ISBE process.
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