Detection of THz radiation with devices made from wafers with HgTe and InSb quantum wells

In this study we present measurements of the Terahertz (THz) photoconductivity of 2D electron system realized at HgTe∕HgCdTe and AlInSb∕InSb∕AlInSb quantum wells (QWs) in Corbino geometry (inner and outer radius: 500 μm and 1500 μm) with different mobilities and electron densities. To characterize the devices, the Shubnikov‐de Haas (SdH) effect up to magnetic fields B of 7T and current‐voltage (I‐V) characteristics at various magnetic fields were measured. The THz radiation is provided by a p‐Ge laser which operates with a magnetic field and a high voltage for the electrical pumping. The stimulated emission is caused by transistions between Landau levels of light holes [1]. The laser is tunable in the range between 1.7 to 2.5 THz (corresponding to wavelengths between 120 to 180 μm or energies of 7 to 12 meV). The laser is pulsed with a pulse rate of 1 Hz and pulse lengths of about 1 μs with low switching times (about 20 ns). The monochromatic THz radiaton is tranferred to our samples via a 0.32m long brass waveguide immersed in liquid Helium. The detection of a change in the conductivity of the sample due to absorption of THz‐radiation (photoresponse) requires a low‐noise circuit. For the Corbino‐shaped samples the photoresponse (PR) is measured via a resistor RV of 1 kΩ. The signal is transferred via in a high‐frequency cable and detected with a digital oscilloscope.