Accurate equivalent circuit model for millimetre-wave UTC photodiodes

Area of Science:

• Optoelectronics
• Terahertz (THz) technology
• Semiconductor device physics

Background:

• Uni-travelling carrier photodiodes (UTC-PDs) are crucial for high-frequency applications.
• Understanding their impedance is key to efficient integration with antennas.
• Existing models fail to explain measured impedance characteristics at high frequencies.

Purpose of the Study:

• To comprehensively study the impedance and frequency photo-response of UTC-PDs up to 110 GHz.
• To develop a new model for UTC-PD impedance that accurately reflects experimental data.
• To optimize the coupling efficiency between UTC-PDs and THz antennas.

Main Methods:

• Experimental measurements of UTC-PD impedance and photo-response up to 110 GHz.
• Analysis of experimental data using standard and a proposed novel impedance model.
• Comparison of the proposed model's predictions with experimental results.

Main Results:

• Measured UTC-PD impedance deviates significantly from predictions based on the standard junction-capacitance/series-resistance model.
• The proposed new model shows good agreement with the experimental impedance data.
• The study provides insights into optimizing UTC-PD and THz antenna coupling efficiency.

Conclusions:

• The standard model is insufficient for describing UTC-PD impedance at high frequencies.
• A novel impedance model is presented, offering accurate predictions for experimental data.
• This work enables better prediction and maximization of power output for antenna-integrated UTCs.