Abstract
Near-infrared photoabsorption spectra of individual dots of gallium antimonide (GaSb) epitaxially grown on a silicon substrate were investigated by nanoscale-resolved spectroscopic measurements and by imaging through scanning tunneling microscopy (STM). With a short acquisition time of a few minutes, photomodulated current spectroscopy (STM-PMCS), based on STM without a tunneling current, showed that our samples exhibited photoabsorption with a peak centered at about 0.78 eV. Spatial variations in STM-PMCS imaging arose from differences in dot sizes. However, the STM-PMCS images were insufficiently unambiguous to permit interpretation of the signal origin in the tunneling region, because a tip-expansion effect could have arisen through photointensity modulation. Spectral features revealed by STM-based electric field modulation spectroscopy (STM-EFMS), which is free of the tip-expansion effect, showed a significant size-dependent energy shift at around 0.8 eV that was attributed to a quantum-confinement effect on the bound states of the GaSb quantum dots. Our approach, which utilizes the merits of both STM-PMCS and STM-EFMS, is efficient in elucidating the photoabsorption properties of nanoscale objects.
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Schedule a callMore From: Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena
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