Study of III-nitride growth kinetics by molecular-beam epitaxy
Moseley, Michael William
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Since the initial breakthroughs in structural quality and p-type conductivity in GaN during the late 1980s, the group-III nitride material system has attracted an enormous amount of interest because of its properties and applications in both electronics and optoelectronics. Although blue light-emitting diodes have been commercialized based on this success, much less progress has been made in ultraviolet emitters, green emitters, and photovoltaics. This lack of development has been attributed to insufficient structural and electrical material quality, which is directly linked to the growth of the material. The objective of this work is to expand the understanding of III-nitride growth towards the improvement of current device capabilities and the facilitation of novel device designs. Group-III nitride thin films are grown by molecular-beam epitaxy in a pulsed, metal-rich environment. The growths of nitride binaries and ternaries are observed in situ by transient reflection high-energy electron diffraction (RHEED) intensities, which respond to the behavior of atoms on the growing surface. By analyzing and interpreting these RHEED signatures, a comprehensive understanding of nitride thin film growth is obtained. The growth kinetics of unintentionally doped GaN by metal-rich MBE are elucidated, and a novel method of in situ growth rate measurement is discovered. This technique is expanded to InN, highlighting the similarity in molecular-beam epitaxy growth kinetics between III-nitride binaries. The growth of Mg-doped GaN is then explored to increase Mg incorporation and electrical activation. The growth of InxGa1-xN alloys are investigated with the goal of eliminating phase separation, which enables single-phase material for use in photovoltaics. Finally, the growth of unintentionally doped and Mg-doped AlGaN is investigated towards higher efficiency light emitting diodes. These advancements in the understanding of III-nitride growth will address several critical problems and enable devices relying on consistent growth in production, single-phase material, and practical hole concentrations in materials with high carrier activation energies.
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