Native point defects in indium nitride and indium-rich indium gallium nitride alloys

The recent discovery of the narrow bandgap of InN of 0.7 eV has attracted strong scientific interests on the fundamental properties and possible applications of InN and its ternary alloys. The first part of this thesis was inspired by the proposal of using InxGa1-x N alloy to build high efficiency solar cell for space applications. To test the irradiation hardness of InN and InxGa 1-xN, we have irradiated numerous samples with energetic particles (1-2 MeV electrons, protons, and 4He+ particles). InN and InxGa1-xN displayed superior radiation hardness over current multi-junction solar cell materials such as GaAs and GaInP in terms of electronic and optical properties. Free electron concentrations in InN and In-rich InxGa 1-xN increased with irradiation dose but saturated at a sufficiently high damage dose. According to the amphoteric defect model, the doping effect and the electron concentration saturation originates from irradiation-induced native donors and Fermi level pinning at the Fermi level stabilization energy (EFS). The EFS, an average energy of all localized native defects, dictates the electronic properties (donor or acceptor) of the native point defects. The electron concentration saturation and Fermi level pinning lead to profound changes in the optical properties. Absorption spectra shift to higher energy due to the conduction band-filling effect (Burstein-Moss shift). Photoluminescence (PL) signals broadened and shifted to higher energy as the k-conservation rule collapsed with irradiation damage. The PL intensity of increased slightly with higher carrier concentration before it became quenched by the irradiation-induced carrier traps. Capacitance-voltage (CV) measurements show that the pinning of the surface Fermi energy at EFS is also responsible for the surface electron accumulation effect in InN and In-rich In xGa1-xN alloys.; The second part of this thesis focuses on the hydrostatic pressure dependence of group III-nitride alloys. The hydrostatic pressure dependence of the narrow bandgap of InN, In-rich InxGa1-x N (0 < x ≤ 0.5), and InyAl 1-yN (y = 0.25) alloys was measured by optical absorption and PL experiments with samples mounted in diamond anvil cells. The pressure coefficient of InN was experimentally determined for the first time to be 3.0+/-0.1 meV/kbar. The PL signal exhibits a much weaker pressure dependence than the direct bandgap, which is attributed to the emission process associated with highly localized states. Using the localized states emission as an energy reference, the deformation potential of the band edges of InN and In0.5Ga0.5N were determined.