Plasmonic and Magneto-Optical Properties of Nonstoichiometric Indium Nitride Nanostructures

Abstract

Localized surface plasmon resonance (LSPR) in semiconductor nanostructures have attracted intense attention recently for its broad application in bio-imaging, chemical sensing, photocatalysis, and photovoltaics. Compared to the LSPR in metallic nanocrystals (NCs), LSPR in semiconductor NCs is highly tunable in the infrared region by tailoring chemical composition and stoichiometry. Moreover, LSPR along with external magnetic field allows the exploration of magneto-plasmonic coupling in single-phase semiconductors, opening up the magneto-optical ways to control charge carriers. In this thesis, we focus on the LSPR as well as magneto-optical properties of indium nitride (InN), providing valuable insights into the insufficiently researched III-V group semiconductors. Wurtzite phase InN NCs were successfully synthesized using the low-temperature colloidal method, and the plasmon intensity is tunable by changing the synthesis environment and varying doping concentrations of aluminum and titanium ions. Due to the combined effects of conduction band non-parabolicity and intraband transition, our InN NCs with different plasmon intensities have an almost fixed plasmonic energy of 0.37 eV. Besides, the optical bandgap of pure InN NCs ranges from 1.5 to 1.75 eV, depending on the reaction conditions, while that of the Al and Ti-doped InN varies from 1.65 to 1.85 eV. The plasmon-dependent phonon change is evaluated by the Raman spectroscopy. Differences in the longitudinal-optical (LO) phonon mode was observed for InN with high and low plasmon intensity. The magneto-optical properties of InN NCs were measured by the magnetic circular dichroism (MCD). The field-dependence and temperature-independence of the measured MCD spectra were investigated, and the plasmon-induced polarization of carriers was demonstrated. Tuning of the carrier polarization by varying LSPR and external magnetic field corroborates the hypothesis of non-resonant coupling between plasmons and excitons in a single-phase semiconductor. The results of this work demonstrate that LSPR can act as a degree of freedom in manipulating electrons in technologically-important III-V nanostructures and lead to potential applications in photonics and quantum computing at room temperature. Finally, InN nanowires (NWs) with LSPR were fabricated via low-temperature chemical vapor deposition (CVD) approach, laying the groundwork for the future research of LSPR and magneto-plasmonics in a one-dimensional system.