Broadband GaP contact-grating terahertz source pumped at 3.9 µm.

Area of Science:

• Solid-state physics
• Terahertz (THz) photonics
• Semiconductor device physics

Background:

• Gallium phosphide (GaP) is a promising material for optoelectronic devices.
• Terahertz (THz) sources are crucial for various scientific and technological applications.
• Contact-grating structures offer potential for efficient THz generation.

Purpose of the Study:

• To demonstrate a novel GaP semiconductor contact-grating THz source.
• To investigate the scalability and performance characteristics of the THz source.
• To explore the limiting factors of THz generation efficiency.

Main Methods:

• Fabrication of a GaP semiconductor contact-grating THz source with a trapezoidal groove profile.
• Pumping the source with a mid-infrared wavelength of 3.9 μm.
• Characterization of THz generation efficiency and saturation mechanisms.

Main Results:

• Demonstration of a GaP contact-grating THz source operating from 0.2 THz to 6 THz.
• Source scalability to electric fields exceeding 1 MV/cm.
• Achieved high usable pump intensities up to 310 GW/cm² due to 9-photon absorption.
• Observed saturation of THz generation efficiency at ~160 GW/cm² due to free-carrier generation.

Conclusions:

• The demonstrated GaP THz source exhibits significant potential for high-field applications.
• Free-carrier generation, driven by multiphoton and Keldysh tunnel ionization, limits THz generation efficiency.
• The plane-parallel geometry and material properties of GaP enable high-power THz generation.