# 6.2-GHz modulated terahertz light detection using fast terahertz quantum well photodetectors

## TL;DR

This paper introduces the first fast semiconductor-based terahertz quantum well photodetectors capable of gigahertz modulation response, enabling rapid detection of terahertz radiation for applications like imaging and communications.

## Contribution

The work presents a novel design of terahertz quantum well photodetectors with gigahertz bandwidth, significantly surpassing traditional thermal detectors in speed and response.

## Key findings

- Achieved 6.2-GHz modulation response bandwidth.
- Successfully detected terahertz light from a quantum cascade laser.
- Demonstrated potential for frequency stability and phase noise analysis.

## Abstract

The fast detection of terahertz radiation is of great importance for various applications such as fast imaging, high speed communications, and spectroscopy. Most commercial products capable of sensitively responding the terahertz radiation are thermal detectors, i.e., pyroelectric sensors and bolometers. This class of terahertz detectors is normally characterized by low modulation frequency (dozens or hundreds of Hz). Here we demonstrate the first fast semiconductor-based terahertz quantum well photodetectors by carefully designing the device structure and microwave transmission line for high frequency signal extraction. Modulation response bandwidth of gigahertz level is obtained. As an example, the 6.2-GHz modulated terahertz light emitted from a Fabry-P\'{e}rot terahertz quantum cascade laser is successfully detected using the fast terahertz quantum well photodetector. In addition to the fast terahertz detection, the technique presented in this work can also facilitate the frequency stability or phase noise characterizations for terahertz quantum cascade lasers.