Magnetotransport and THz-Optical Investigations at Devices with HgTe Quantum Wells

We investigated the magnetoconductivity and the Terahertz (THz) photo-conductivity of devices with HgTe quantum wells embedded in barrier layers of HgCdTe. For the photoconductivity measurements, a THz laser system (p-Ge-Laser) is applied. This laser uses transitions between Landau levels of light holes in Ge and emits laser pulses in the wavelength range 120 mu m < lambda < 180 mu m. The THz laser radiation is used in order to excite charge carriers over the Landau-gap. The response of the sample to the laser impulses is in 2D-samples in the quantum Hall (QH) regime measured in order to receive data of the relaxation of the charge carriers. In this presentation we present photoconduction measurements of the HgTe-quantum well in Hall bar, Corbino as well as combined Corbino-Hall bar geometry in the QH-regime. The material system HgTe/HgCdTe is characterized by a small effective mass (compared to GaAs, in our case 0.023 m (0)) and accordingly smaller magnetic fields for the appropriate cyclotron energy. Thus, this material combination provides the opportunity to make THz detectors using magnetic fields below 2 T for operation.