Monolithic Echo-less Photoconductive detectors for Terahertz Time-domain Spectroscopy

A paper on Echo-less photoconductive switches as high resolution detectors has been published in Applied Physics Letters by the group at CNRS-LPA. Photoconductive (PC) switches are powerful and convenient devices for time-resolved spectroscopy, with the ability to operate both as sources and detectors of terahertz (THz) frequency pulses. However, reflection of the emitted or detected radiation within the device substrate itself can lead to echoes that inherently limits the spectroscopic resolution achievable from their use in time-domain spectroscopy (TDS) systems. In this work, we demonstrate a design of low-temperature-grown-GaAs (LT-GaAs) iPC switches for THz pulse detection that suppresses such unwanted echoes. This is realized through the growth of a buried multilayer LT-GaAs structure, which after wafer bonding to a metal-coated host substrate, results in an iPC switch with a metal plane buried at a subwavelength depth below the LT-GaAs surface. Using this device as a detector enables echo-free THz-TDS and high-resolution spectroscopy. As a proof-of-principle, the 212-221 and the 101-212 rotational lines of water vapor have been spectrally resolved, demonstrating a spectral resolution below 10 GHz.

The full publication can be accessed here and here