Materials for the ultra-broadband terahertz detection

• Applicant: Dmytro Kamenskyi, Ph.D.
• Subject Area: Experimental Condensed Matter Physics ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 497756533

Electromagnetic radiation in the terahertz spectral range (0.3 - 3 THz, 1.2 - 12 meV) can excite vibrational, translational, rotational, torsional modes of molecules and zone-center phonons in crystals. Moreover, it can be resonant with low-energy orbital excitations of transition (d and f) metals and spin-wave excitations of magnetically ordered materials. Thus, THz spectroscopy is a perfect tool for identifying, imaging and studying a great variety of materials. Recent technological advances prove that THz spectroscopy has an excellent potential beyond scientific research: in medical, industrial, and security applications. However, further effort is needed to bring it to a level of routine application.A significant obstruction for the wide usage of the THz spectroscopy is the lack of convenient optical components for these frequencies (so-called ‘terahertz gap’). In the last decades, enormous effort in the development of THz radiation sources (including large-scale facilities) results in a variety of THz radiation sources, particularly high-power pulsed sources. These short-pulse THz sources require fast broadband detectors. However, the detection technologies are lacking behind utilizing relatively slow or/and narrow-band detectors, limiting the scientific and application potential of the entire field. This project aims to investigate heavily doped germanium single crystals (Ge), a most promising material for high-sensitive broadband radiation detection within and beyond THz frequencies with nanosecond time resolution. Employing variety of experimental techniques, we will reveal the carrier dynamic in the THz range, which remains the hot topic of solid-state physics for many decades.This project focuses on the investigations of Ge doped with shallow impurities (Gallium, Antimony). In contrast to the previous THz research in Ge, we will concentrate on the transition between heavy and light holes sub-bands of the valence band to enhance the free carrier response between 1 and 2 THz. We will look for the optimal combination of impurities concentration and the external stimuli keeping in mind the extrinsic conductivity, which shall remain good enough for the successful performance above 2 THz. A comprehensive experimental study by such methods as magnetotransport, Hal effect, photoconductivity, cyclotron resonance, far-infrared and Raman spectroscopies with be completed by the state of art experiments using the large scaly research facilities FELIX and HFML: a unique combination of the Free electron laser and high magnetic field laboratories at the Radboud University (Nijmegen, Netherlands).

• DFG Programme: Research Grants