Photoluminescence Imaging in Semiconductor Nanostructures
Effects of nano-structure and localized states are investigated by spectroscopic imaging with subwavelength spatial resolution. Examples of materials of interest are quantum dots (a nano-engineered material targeted for solar cell applications in a number of schemes, such as impact ionization or multiple exciton generation, intermediate band solar cells, and improved thermoelectric materials). Major equipment consists of: an HR640 single grating spectrometer (high dispersion gratings), Princeton Instruments SPEC-10 back illuminated CCD, Millenia 5W pump laser and KML Ti:Sapphire femtosecond laser. A closed-loop piezo electric stage (PI 200mm x200mmx20mm range of motion) point-illuminates a Solid Immersion lens system housed in a liquid Helium bath-style cryostat (Oxford OptistatSXM) for spatially resolved photoluminescence imaging. This system will be extended to near-field imaging (as an example, see figure 3 below), wherein an optical fiber is tapered to a subwavelength dimension and used to illuminate and analyze semiconductor surfaces with subwavelength spatial resolution A closed cycle refrigeration unit and optical cryostat are also available for far-field PL measurements, and a time-correlated single photon counting card is on order for lifetime measurements. The system, and miscellaneous optics and associated instrumentation are housed on a 3rd 4x8 optical table.
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