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In recent years ZnO has received renewed interest due to its exciting semiconductor properties and remarkable ability to grow nanostructures. ZnO is a wide band gap semiconductor, allowing many potential future applications including electronic nanoscale devices, biosensors, blue/UV light emitters, and transparent conductors. There are many potential challenges that keep ZnO from reaching a full device potential. The biggest challenge is what the role native point defects play in the fabrication of high quality Ohmic and Schottky contacts. The following work examines the impact of these native point defects in the formation of Schottky barriers and charge transport at ZnO interfaces. We have used depth-resolved cathodoluminescence spectroscopy and nanoscale surface photovoltage spectroscopy to measure the dependence of native point defect energies and densities on Mg content, band gap, and lattice structure in non-polar, single-phase MgxZn1-xO (0 < x < 0.56) alloys on r-plane sapphire substrates. Based on this wide range of alloy compositions, we identified multiple deep level emissions due to zinc and oxygen vacancies. DRCLS allows us to probe buried interfaces. Due to a strong Fermi-level mismatch, about 10% of the electrons in a 5-nm-thick highly-Ga-doped ZnO layer on an undoped ZnO buffer layer transfer to the ZnO causing the measured Hall-effect mobility of the GZO/ZnO combination to remarkably increase from 34 cm2/V-s, in thick GZO, to 64 cm2/V-s. Assuming the interface is abrupt, theory predicts μH = 61 cm2/V-s. The assumption of abruptness in [Ga] and [VZn] profiles is confirmed directly with a differential form of depth-resolved cathodoluminescence spectroscopy coupled with X-ray photoelectron spectroscopy.We probed the IrOx/ZnO interface. IrOx and other metal oxides exhibit higher Schottky barriers than their pure metal counterparts. DRCLS with I-V and 1/C2-V barrier height and carrier profile measurements showed high zinc vacancy VZn and CuZn defect densities that compensate free carrier densities, increase depletion widths, and form higher effective barriers than Ir/ZnO contacts. Zn-polar versus O-polar ZnO interfaces with IrOx exhibit 40% higher VZn + CuZn interface segregation and lower carrier densities within a wider depletion region. The depth of VZn density segregation and the Zn-deficient layer thickness measured microscopically both match the depletion width, and applied electric fields comparable to spontaneous polarization fields across similar layers display analogous defect segregation. These results account for the difference in polarity-dependent segregation due to the electric field-driven diffusion of native defects near ZnO interfaces.By establishing the role that defects play in the effective barrier height we attempted to form Ohmic and Schottky contacts to ZnO nanowires. A Pt ion beam alone can form Ohmic, Schottky, or blocking contacts to ZnO nanowires with the same metal on the same wire by controlling native point defects at the intimate metal-semiconductor interface. Cathodoluminescence spectroscopy both laterally and in depth gauges the nature, density, and spatial distribution of specific native point defects inside the nanowires and at their metal interfaces. These results demonstrate the importance of point defects on electrical properties of metal contacts to ZnO nanowires and present methods to tailor contact electronic properties of nanowires in general.