Dynamically modulating the photocarrier lifetimes in silicon for single-pixel terahertz imaging

Xavier Romain¹, Rayko Stantchev^3,2*, Sophie L. Pain¹, Tim Niewelt^1,4, Nicholas Grant¹, Emma Pickwell-Macpherson², John Murphy¹

¹School of Engineering, University of Warwick, Coventry, UK
²Department of Physics, University of Warwick, Coventry, UK
³Department of Physics, National Sun Yat-sen university, Kaohsiung, Taiwan
⁴Laboratory for Photovoltaic Energy Conversion, University of Freiburg, Freiburg, Germany

* Presenter:Rayko Stantchev, email:rayko.stantchev@g-mail.nsysu.edu.tw

Modulating terahertz (THz) radiation via the active means of photo-excitation in semiconductors offers a pathway to THz modulators that are reconfigurable over and over again with no manufacturing involved. However the carrier lifetime is directly related to the switching time as well as the modulation depth. In this work, we report silicon-based THz photomodulator scheme that allows tuning of the effective charge carrier lifetime, which allows us to optimize the switching behavior. We passivate the silicon surface by growing a layer of silicon oxide, then we use atomic layer deposition of hafnium oxide and finally we spin coat a layer of a conductive polymer (PEDOT:PSS). The conductive polymer allows us to electrically gate the whole silicon surface thereby changing the effective carrier lifetime. We show that this can be used to improve the photo-modulation of THz, and this can improve the signal to noise ration of single-pixel THz imaging.

Keywords: single-pixel imaging, silicon passivation, terahertz imaging