Efficient on-chip terahertz generation and detection with GaN photoconductive emitters

Area of Science:

• Optoelectronics
• Solid-state physics
• Terahertz science

Background:

• Terahertz (THz) generation via photoconductive emitters offers efficient optical photon down-conversion, unbound by the Manley-Rowe relation.
• Current THz photoconductive devices using materials like Gallium Arsenide (GaAs) are limited in efficiency due to semiconductor properties.

Purpose of the Study:

• To demonstrate efficient terahertz wave generation using Gallium Nitride (GaN), a large bandgap semiconductor.
• To investigate the excitonic contribution to GaN's electro-optic response and leverage it for enhanced THz emission.

Main Methods:

• Utilized first-principles calculations and experimental investigations to study the excitonic Stark shift in GaN under static electric fields.
• Developed a novel ultraviolet (UV) pump-probe spectroscopy technique for in-situ characterization of THz electric field strength.
• Fabricated GaN photoconductive emitters in a coplanar stripline waveguide configuration.

Main Results:

• Observed a robust excitonic Stark shift in GaN, confirming its suitability for electro-optic modulation.
• Demonstrated that terahertz power scales quadratically with both optical excitation power and applied electric field.
• Achieved optical-to-terahertz conversion efficiencies approaching 100% within the 0.03-1 THz bandwidth at high bias fields (116 kV/cm).

Conclusions:

• GaN is a promising material for highly efficient terahertz photoconductive emitters, surpassing limitations of existing GaAs-based devices.
• The demonstrated UV pump-probe spectroscopy provides an effective method for characterizing THz generation.
• Further optimization of GaN devices holds potential for even higher optical-to-terahertz conversion efficiencies.