Approaching the intrinsic exciton physics limit in two-dimensional semiconductor diodes

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) semiconductors exhibit unique photophysical properties due to their reduced dimensionality.
• A gap exists between fundamental 2D semiconductor photophysics and practical device performance, often limited by interfacial disorder.
• Contact-induced recombination hinders the realization of intrinsic photophysics in 2D semiconductor devices.

Purpose of the Study:

• To suppress contact-induced recombination and achieve device performance dictated by intrinsic photophysics in 2D semiconductor diodes.
• To investigate the role of exciton dynamics and charge interactions in 2D semiconductor devices.
• To explore the potential for creating more efficient optoelectronic devices based on intrinsic 2D semiconductor properties.

Main Methods:

• Fabrication of 2D semiconductor diodes using van der Waals contacts with minimal interfacial disorder.
• Utilized a split-gate geometry for independent modulation of electron and hole doping in tungsten diselenide (WSe2) diodes.
• Employed time-resolved photoluminescence and scanning photocurrent microscopy to study photophysical properties and device performance.

Main Results:

• Achieved nearly intrinsic photophysics-dictated device performance by suppressing Shockley-Read-Hall recombination.
• Observed an unusual peak in short-circuit photocurrent at low charge densities.
• Demonstrated a significant decrease in exciton lifetime with increasing doping due to exciton-charge Auger recombination.

Conclusions:

• An exciton-diffusion-limited model successfully explains the charge-density-dependent short-circuit photocurrent.
• Highlighted the critical roles of exciton diffusion and two-body exciton-charge Auger recombination in 2D devices.
• Showcased the potential of leveraging intrinsic 2D semiconductor photophysics for enhanced optoelectronic device efficiency.