Synchrotron radiation-based characterization of GaN- based MQW structures and strongly correlated materials

The following dissertation applies synchrotron radiation-based characterization techniques to the fields of gallium nitrides, multiferroic manganites, and self-assembled nano-domain oxide films. These material systems were chosen due to their unusual properties and potential device applications, which have made them very attractive to the scientific community. Synchrotron-based High Resolution X-ray Diffraction (HRXRD) was used to characterize the structural properties of GaN-based multiple quantum well (MQW) structures grown on trapezoidal shaped GaN ridges. Results where interpreted within the framework of vapor-phase diffusion and surface-migration effects during the metalorganic vapor phase epitaxial growth. The relatively short diffusion length of group- III precursors and growth enhancement, due to facet migration was found to have significant effects on the MQW formation. The use of synchrotron based HRXRD and in particular cross-sectional reciprocal space mapping (RSM) was then extended to studying the intriguing structural properties of a ZnMnGaO_4 film epitaxially grown on MgO (001) substrate. The results of this study helped in identifying the ZnMnGaO_4 film, as consisting of a self-assembled nano- checkerboard structure of highly aligned and regularly spaced vertical nanorods. The results demonstrated the importance of lattice distortion symmetry at the phase boundaries as a means for the coherent coexistence of two domain types within the film volume. Synchrotron-based far-infrared spectroscopy was performed at low temperatures on the single crystal multiferroic manganite HoMn_2O_5. A number of the infrared-active excitations were attributed to electric-dipole transitions between ligand-field split states of Ho^{3+} ions. It is proposed that the proximity in energy between magnons and Ho^{3+} ligand fields (LF) might connect the magnetism and dielectric properties of this compound through coupling with the Mn spin structure.

Name thesis:degree_name

Doctor of Philosophy in Applied Physics - (Ph.D.)

Discipline thesis:degree_discipline

Federated Physics Department

Year

2009

Author dc:creator

• O'Malley, Sean M.

Contributors dc:contributor

• Andrei Sirenko
• Daniel-Dennis McAlevy Bubb
• John Francis Federici

• Synchrotron
• Multiferroic
• Self-assembled
• X-ray diffraction
• Far-infrared spectroscopy
• Group-III nitride
• Other Physics

Repository record dc:identifier

https://digitalcommons.njit.edu/dissertations/896

OAI identifier oai:identifier

oai:digitalcommons.njit.edu:dissertations-1951