Extremely efficient multiple electron-hole pair generation in carbon nanotube photodiodes

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Single-walled carbon nanotubes (SWCNTs) are promising nanomaterials for electronic and optoelectronic applications.
• Photodiodes based on p-n junctions are crucial components in light detection and energy conversion.

Purpose of the Study:

• To investigate the mechanism of highly efficient electron-hole pair generation in SWCNT p-n junction photodiodes.
• To explore the potential of impact excitation for next-generation photovoltaic devices.

Main Methods:

• Fabrication and characterization of SWCNT p-n junction photodiodes.
• Optical excitation experiments targeting specific electronic subbands (E22).
• Analysis of current-voltage (I-V(SD)) characteristics and photocurrent responses.
• Spatially and spectrally resolved photocurrent measurements.
• Temperature-dependent device studies.

Main Results:

• Observed highly efficient generation of electron-hole pairs through impact excitation.
• Identified distinct photocurrent steps in I-V(SD) characteristics at voltage intervals corresponding to the band-gap energy (E(GAP)/e).
• Demonstrated that excitation into the E22 subband triggers multiple electron-hole pair generation from a single hot carrier.
• Photocurrent studies confirmed the role of impact excitation in this multi-carrier generation process.

Conclusions:

• Impact excitation in SWCNT p-n junction photodiodes enables ultra-efficient electron-hole pair generation.
• The observed photocurrent steps provide evidence for multiple exciton generation from hot carriers.
• This phenomenon holds significant potential for developing advanced, highly efficient photovoltaic technologies.