Electrical control of second-harmonic generation in a WSe2 monolayer transistor

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optoelectronics

Background:

• Nonlinear optical frequency conversion is essential in photonics but difficult to tune.
• Dynamical control of optical nonlinearities is typically limited to laboratory spectroscopy.
• Atomically thin semiconductors offer unique properties for optical applications.

Purpose of the Study:

• To demonstrate electrical control of second-order optical nonlinearities in monolayer WSe₂.
• To investigate the tunability of second-harmonic generation (SHG) via electrostatic doping.
• To explore the potential of 2D semiconductors for tunable nonlinear optical devices.

Main Methods:

• Fabrication of a field-effect transistor using monolayer WSe₂.
• Measurement of second-harmonic generation intensity under varying electrostatic doping conditions.
• Analysis of exciton charging effects and their influence on nonlinear optical properties.

Main Results:

• Second-harmonic generation intensity tunable by over an order of magnitude at low temperature and a factor of four at room temperature.
• Tunability attributed to strong exciton charging effects in monolayer semiconductors.
• Observed counter-circular polarization of SHG, consistent with valley selection rules.

Conclusions:

• Electrostatic doping provides a powerful mechanism for electrically controlling nonlinear optical responses in 2D semiconductors.
• Monolayer WSe₂ exhibits significant, temperature-dependent tunability of its nonlinear optical properties.
• This work establishes a foundation for developing chip-scale, electrically tunable nonlinear optical devices.