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.

Figure 3: Physical confinement of light is achieved utilizing subwavelength apertures formed at the apex of a tapered single mode optical fiber. This aperture is used to illuminate and collect luminescence locally, with subwavelength spatial resolution. The above example illustrates the spatial and spectral localization of excitonic emission in an epitaxially grown GaInP crystal. Simultaneous topographic and spectrally-resolved luminescence images are obtained (in this case at T=5K)[1-3].

 Related Publications

[1] S. Smith, A. Mascarenhas, S. P. Ahrenkiel, M. C. Hanna, and J. M. Olson, "Spatially resolved below-gap emission in partially ordered GaxIn1-xP alloys," Phys. Rev. B 68 035310 (2003).
[2] S. Smith, A. Mascarenhas, and J. M. Olson , "Magnetophotoluminescence of quantum confined states in ordered GaxIn1-xP with 200 nanometer resolution," Phys. Rev. B 68, 153202 (2003).
[3] S. Smith, H.M. Cheong, B.D. Fluegel, J.F. Geisz, L.L. Kazmerski, A. Mascarenhas, "Spatially resolved photoluminescence in partially ordered GaInP2," Appl. Phys. Lett. 74 (5) 706-8 (1999).

Nano Science and Engineering PhD Program
South Dakota School of Mines and Technology
501 E. St. Joseph St, Rapid City, SD, 57701
Nano SE PhD Info   Tel: 605-394-5268