Deep levels in 1.8 MeV proton irradiated n-type GaN were systematically characterized using deep level transient spectroscopies and deep level optical spectroscopies. The impacts of proton irradiation on the introduction and evolution of those deep states were revealed as a function of proton fluences up to 1.1 × 10¹³ cm⁻². The proton irradiation introduced two traps with activation energies of E_C - 0.13 eV and 0.16 eV, and a monotonic increase in the concentration for most of the pre-existing traps, though the increase rates were different for each trap, suggesting different physical sources and/or configurations for these states. Through lighted capacitance voltage measurements, the deep levels at E_C - 1.25 eV, 2.50 eV, and 3.25 eV were identified as being the source of systematic carrier removal in proton-damaged n-GaN as a function of proton fluence.

The location and nature of fixed charge states in high-k/GaN metal-oxide-semiconductor capacitor structures are characterized by analyzing flatband voltage shifts in high-frequency capacitance-voltage measurements. It is shown that a significant fixed, positive sheet charge forms at Al₂O₃/GaN interfaces, but not at HfO₂/GaN interfaces. Furthermore, an interface dipole is created at HfO₂/Al₂O₃ interfaces, which causes an abrupt shift in the flat band voltage as HfO₂ is introduced to form HfO₂/Al₂O₃ bilayer dielectrics. The observed dependence of the flatband voltage shift on the relative thicknesses of the dielectrics comprising the bilayer dielectrics is discussed.

Quantitative measurements of interface state density and energy distribution profiles within Al₂O₃/GaN interfaces were obtained by constant capacitance deep level transient spectroscopy and deep level optical spectroscopy (CC-DLTS/DLOS). The new application of CC-DLOS to interface state measurement is described, which allows interrogation of very deep interface states. A series of Al₂O₃/GaN metal-insulator-semiconductor (MIS) devices prepared as a function of Al₂O₃ thickness via atomic layer deposition, on NH₃-MBE-grown n-type Ga-polar GaN layers enabled a systematic study. The overall shape and magnitude of the interface trap distribution, D_it, were determined to be nearly identical, independent of Al₂O₃ thickness. The Al₂O₃/GaN D_it spectra had an overall U-shape with D_it ∼10¹² cm⁻² eV⁻¹ near the conduction band edge, ∼10¹¹ cm⁻² eV⁻¹ mid-gap, and ∼10¹⁴ cm⁻² eV⁻¹ near the valence band edge. However, the interface states near the GaN conduction band showed a slight inverse dependence on Al₂O₃ thickness, suggestive of annealing effect during deposition. The high near valence band state concentrations are consistent with expectations from residual carbon impurities at the GaN surface. A method for discriminating between bulk and interface states in the CC-DLTS signal is demonstrated, using the results on MIS capacitors in combination with spectroscopy results on a Schottky diode structure.

A comprehensive analysis of forward and reverse current of Ga-face GaN p-n junctions grown by ${\text{NH}}_3$ molecular beam epitaxy $\left({\text{NH}}_3\text{-MBE}\right)$ on metal organic chemical vapor deposition (MOCVD) GaN:Fe on sapphire is presented. ${\text{NH}}_3\text{-MBE}$ has a great potential for growing low leakage vertical devices due to its nitrogen-rich growth. Diodes with the lowest n-doping of $\text{n}\sim 3.5\times {10}^{17}{\text{cm}}^{-3}$ exhibit an extremely low reverse current of $2.6\times {10}^{-7}\text{A}/{\text{cm}}^2$ at −40 V and an ideality factor of 1.3, which is lower than the state-of-the-art Ga-face p-n junctions grown on sapphire by MOCVD. An explanation for the difficulty for observing low ideality factors in GaN is presented.

Structural characteristics of aluminum thin films have been grown on the 1 × 1, 7 × 7, and √3 × √3 reconstructed Si (111) surfaces by molecular beam epitaxy demonstrating a connection between the nucleation kinetics and grown-in defects of metamorphic epitaxial thin films. High resolution x-ray diffraction symmetric scans and (111) pole figures show that growth on the 1 × 1 reconstructed Si surface produces polycrystalline Al with (100) and (111) diffraction peaks and a large degree of growth twin as determined by a sixfold symmetric pole figure. Growth on the 7 × 7 reconstructed Si surface results in a twinned crystal exhibiting only Al (111) peaks with a sixfold symmetric pole figure. Growth of Al on the √3 × √3 reconstructed surface realizes nearly twin-free single crystal Al (111) film. Atomic force microscopy demonstrates that the Al film roughness improves with crystal quality. Scanning transmission electron microscopy (STEM) shows the twins originate at the substrate/film interface and extend to the film surface indicating that they are growth defects that form during the first few layers of aluminum growth. In addition, STEM indicates that the misfit strain is relaxed within a few monolayers of the interface through a periodic array of misfit dislocations.