CHARACTERIZATION OF SEMICONDUCTOR NANOWIRES USING RAMAN SPECTROSCOPY AND MULTIFUNCTIONAL SCANNING PROBE MICROSCOPY
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Over the past decade, research on wide bandgap semiconductor nanowires has become one of the most active areas within the nanoscience community. Particularly, there has been extensive research on ZnO and GaN nanowires due to their promising applications in next-generation optoelectronics and highly efficient photovoltaics. Central to realizing these applications is a fundamental understanding of physical properties, such as impurity incorporations, phonon dynamics, and carrier transport. Multi-functional scanning probe microscopy and spatially resolved Raman spectroscopy are suitable tools for studying these properties in individual nanowires.Specifically, Raman spectroscopy, aided by mass spectrometry, was used to identify unintentional impurities in ZnO and GaN nanowires and their incorporation route. Phonon dynamics, in particular the enharmonic phonon coupling strength, was also studied by Raman spectroscopy. A near-field scanning photocurrent microscopy was used to directly measure minority carrier diffusion length and to determine its diameter dependence in individual ZnO nanowires. The origin of this diameter dependence was elucidated by surface photovoltage measurements using scanning Kelvin probe force microscopy and finite-element simulations. In addition, a demonstration of probing heat transport along nanowires and across various nanowire device interfaces using scanning thermal microscopy combined with Raman spectroscopy was also presented.