We have studied the photoresponse ͑transmission and photoconductivity of Corbino-shaped devices͒ of structures with InSb quantum wells ͑AlInSb barriers͒. To characterize the devices, the Shubnikov-de Haas ͑SdH͒ effect up to magnetic fields B of 7 T and current-voltage ͑I-V͒ characteristics at various magnetic fields were measured. Some of the samples showed clearly resolvable SdH oscillations. The I-V curves showed pronounced nonlinearities. The phototransmission and the photoconductivity at various terahertz ͑THz͒ frequencies were measured around 2.5 THz generated by a p-Ge laser. From the cyclotron resonance ͑transmis-sion measurements͒ we deduced a cyclotron mass of 0.022m 0 . We also performed photoconductivity measurements on Corbino-shaped devices in the THz frequency range. Oscillations of the photoconductivity with maxima near the minima of the conductivity in the dark were observed. Thus, these devices are potentially suitable for the detection of THz radiation.

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We present an approach to the double-peak structure of the nonresonant ͑bolometric͒ contribution of the photoresponse, measured as a function of the magnetic field for the optically induced breakdown of the quantum Hall ͑QH͒ effect in devices with Corbino geometry. For the optical excitation of our devices, we used a p-Ge laser continuously tunable in the wavelength range of 120 m ՅՅ180 m. In addition to the bolometric signal, we also observed peaks of the photoresponse due to the cyclotron resonance. In the theoretical part of this study, we present calculations on the basis of an electron heating model. Applying this model we provide a qualitative explanation of our experimental results. To get some insight into the amount of increase in the electron temperature of the QH system exposed to terahertz illumination, we also determined the electron temperature of the QH terahertz detector as a function of the electrical ͑Joule͒ heating. Up to about 25 W and at a filling factor of 2, we found a linear increase in the electron temperature with the absorbed power.

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The terahertz (THz) photoconductivity is investigated in HgTe/ HgCdTe-quantum wells (QWs) in Corbino geometry at various wavelengths of excited radiation. The radiation source is a p-Ge cyclotron laser (pulse width about 1 ms, repetition rate 1 Hz) which is tunable in the wavelength range 120 mm < l < 180 mm by an external magnetic field. It is shown that the photoconductivity is caused by the heating of two-dimensional electron gas (2DEG). A rough estimation yields relaxation time around 0.46 ms. Because of the low effective mass, this material system is especially interesting for detector applications. 1 Introduction The terahertz (THz) photoconductivity response via cyclotron resonance (CR) excitation in quantum Hall (QH) devices is studied during almost three decades [1]. The persistent interest in the problem arises not only from the interest in studying the basics of the nonequilibrium carrier dynamics in Laudau-quantized systems but also from a possible application of sensitive THz QH detectors. So far the efforts were concentrated on AIII-BV systems and mainly on GaAsbased heterostructures [2,3]. Narrow gap AIV-BVI systems with their intriguing properties are not investigated in detail with respect to their photoresponse (PR), yet. Such systems are characterized by strong spin-orbit effects and small effective masses of electrons [4] that can be exploited in detector construction.In this work we shed more light on the THz PR in HgTe/ HgCdTe-quantum wells (QWs) by performing spectral and time-resolved measurements. Specific features of the photoconductivity mechanisms are discussed. We found that the photoconductivity is caused by the heating of two-dimensional electron gas (2DEG) and the corresponding relaxation time is around 0.46 ms.