| Various spectroscopic techniques are used to characterize photoconduction mechanisms at nanoscale interfaces within solar energy utilization devices. Barrier heights between metal contacts and silicon nanowires were measured using spectrally resolved scanning photocurrent microscopy (SPCM). Illumination of the metal-semiconductor junction with sub-bandgap photons generates a photocurrent dominated by internal photo- emission of hot electrons. Analysis of the dependence of photocurrent yield on photon energy enables quantitative extraction of the barrier height.;In vapor-liquid-solid (VLS) growth of semiconducting nanowires, it was hypothesized that radial inhomogeneity in dopant concentration arises from a faceted liquid-solid interface present during nanowire growth. Finite element method was used to present a simple growth model to account for 100-fold enhancements in dopant concentration near the VLS trijunction in both B-doped Si and P-doped Ge nanowires. Enhanced doping near the nanowire surface, mapped quantitatively with atom probe tomography, results in a lowering of the effective barrier height. Occupied interface states produce an additional lowering that depends strongly on diameter. The doping and diameter dependencies are explained quantitatively with finite element modeling. The combined tomography, electrical characterization, and numerical modeling approach represents a significant advance in the quantitative analysis of transport mechanisms at nanoscale interfaces that can be extended to other nanoscale devices and heterostructures.;This result motivated the investigation of semiconductor/electrolyte interface in silicon photoanodes with a passivation layer. Using photoelectrochemical spectroscopy, the presence and the photoconduction via interface states were confirmed, and wavelength dependent impedance spectroscopy confirmed that the occupancy of the interface states can be probed under various applied biases and illumination conditions. Two spectroscopic techniques together revealed that the occupancy of the interface states negatively affect the performance by causing the potential loss across the semiconductor/electrolyte interface.;Finally, a new generation of carbon-based nanomaterials is explored as an alternative candidate for the passivation layer. Carbon nanotube, graphene oxide, and graphene were used as building blocks for a passivation layer, each contributing in a unique role as a charge transfer layer, an oxide interlayer, and the protection layer, respectively. |
