Electron distribution and dynamics in semiconductor materials often determine their physical properties, crucial for functionalities and performance in industrial applications. The continued miniaturization of electronic and photonic devices calls for tools to investigate carrier behavior in semiconductors simultaneously on picosecond and nanometer length scales.

Researchers at UC Berkeley have now demonstrated a new type of optical nanoscopy that can measure electron dynamics in semiconductors. They developed a pump-probe optical nanoscopy integrated with near-field scanning optical microscopy and pump-probe optics to enable high resolution at both the spatial and temporal scale.

In addition, this approach applies to a wide variety of semiconductor materials, such as silicon, germanium, and gallium arsenide, as well as other uncommon materials, including 2D materials and ferroelectric materials.

Optical nanoscopy uses ultrafast lasers and an atomic force microscope (AFM) tip with a tip curvature of less than 30 nanometers to monitor the electrons of semiconductors. Researchers illuminate the AFM tip with two laser beams: a pump beam and a probe beam.

After a precisely timed delay, the second beam strikes the tip after the first beam has excited the sample’s electrons. The analysis of the second beam’s scattered light can then be used to determine the local information about electron characteristics.

Jingang Li, lead author and a postdoctoral researcher in Grigoropoulos’ Laser Thermal Lab, said: “Optical nanoscopy may have applications beyond measuring electrons in semiconductor materials.”

“Being a versatile optical diagnostic tool, it can study many other physical phenomena and functional devices, such as phase transitions and data storage.”

“This research is an important step towards exploring and optimizing energy savings for semiconductor-based electronic devices, such as mobile phones, LEDs, industrial solar cells and sensors.”

Magazine reference:

  1. Jingang Li, Rundi Yang, Yoonsoo Rho* et al. Ultrafast optical nanoscopy of carrier dynamics in silicon nanowires. Nano letters. DOI: 10.1021/acs.nanolett.2c04790