Process development of contact and functional layers for novel semiconductors.

摘要

This study is focused on process development regarding Ohmic and Schottky contacts to n-ZnO and the application of functional layers to GaN and InN nanostructures for Hydrogen sensing. Goals of this work are three fold: first is to develop low resistance contacts for n-ZnO with higher thermal stability than typical metal stacks. Second, cryogenic temperatures have been used to deposit metal contacts to n-ZnO in order to increase barrier height at the interface for improved Schottky behavior. Finally, metal functionalization layers of Pt or Pd have been attempted on GaN nanowires and InN nanobelts for Hydrogen sensing.;Ohmic contacts to n-ZnO were fabricated using a variety of robust, refractory materials including TiB2, CrB2, and Ir. Boride contacts were rectifying for lower anneal temperatures but transition to Ohmic behavior at higher temperatures (700°C) and exhibit minimum specific contact resistivity as low as ∼5x10-4 O. cm. Higher temperatures led to severe contact metallurgy intermixing and an increase in specific contact resistivity. Ir contacts exhibited high thermal stability and minimum specific contact resistance of 3.6x10-5 O.cm2 after a 1000°C anneal.;Next, the effect of cryogenic temperatures during deposition of Pd, Pt, Ti, Ni, and Au on n-ZnO was investigated. Deposition at both room and low temperature produced contacts with Ohmic characteristics for Ti and Ni metallizations. By sharp contrast, both Pd and Pt contacts showed rectifying characteristics after deposition with barrier heights between 0.37--0.69 eV. Pd contacts showed an increase in barrier height along with a decrease in ideality factor with increasing annealing temperature. Au deposited at room temperature produced contacts with Ohmic characteristics while cryogenic deposition produced rectifying characteristics. The differences in contact behavior were stable to anneal temperatures of ∼300°C.;Finally, Pd and Pt functionalization layers were deposited to GaN nanowires and InN nanobelts for Hydrogen sensing. Both uncoated nanomaterials show little or no current response upon exposure to hydrogen gas. The addition of a functional layer is shown to dramatically affect response to H2, allowing for hydrogen to be detected down to the hundreds of ppm level. Pd exhibits a greater response to hydrogen than Pt in both cases.