Spectral and Temporal Resolution of THz Detectors based on Quantum Hall Devices with various Geometries
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Spectral and Temporal Resolution of THz Detectors based on Quantum Hall Devices with various Geometries N. G. Kalugin1, C. Stellmach2, Yu. Vasilyev3, A. Hirsch2, G. Hein4, B.E. Sağol4, and G. Nachtwei2 1
Department of Physics, Texas A&M University, College Station, TX 77843, U.S.A. Institut für Angewandte Physik, Technische Universitaet Braunschweig, Mendelssohnstr. 2, D-38106 Braunschweig, Germany 3 A.F. Ioffe Physical Technical Institute, Polytekhnicheskaya 26, 194021 St. Petersburg, Russia 4 Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany 2
ABSTRACT Quantum Hall (QH) systems can work as very sensitive THz detectors. In this work we report on the spectral and temporal resolution of the QH THz photodetectors with different geometries. The spectral resolution of THz QH detectors is of the order of 1-3 meV at photon energies of about 10 meV, depending on bias conditions. The temporal resolution of QH detectors depends on the device geometry. For Corbino-shaped detectors we have demonstrated the devices with response times from 10 ns to over 200 ns. INTRODUCTION Quantum Hall systems (QHS) [1] demonstrate high performance of working as sensitive and tunable THz detectors for wave numbers around 100 cm-1 [2,3]. In this article, we present the results of performance tests of QH THz detectors with different shapes, using THz laser radiation. The radiation source is a p-Ge light-hole cyclotron-resonance laser ([4]). EXPERIMENTAL DETAILS The QH samples used for this study were meander samples [2,3], and circular Corbino devices, patterned photolithographically from GaAs/GaAlAs-heterostructures with a two-dimensional electron system. The meander geometry is preferable for photoconductivity measurements due to the relatively large area and the favourable length-to-width ratio [2,3]. The wafers which meander and Corbino samples are patterned from have electron densities ns in the range of 1.9-3.1·1011cm-2 and mobilities µ4.2K of 100000-1500000 cm2/V s. The parameters of the wafers are presented in the table I. Table I. Parameters of heterostructures at T = 4.2 K. Wafer # 8447 8571 8788 8815
Electron density, cm-2 2.7 ×1011 3.1× 1011 2.0 ×1011 1.9× 1011
Mobility, cm2 /V s 100000 190000 500000 1500000
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The wafers were patterned in 100 µm-wide, 60 mm-long, meander-shaped samples with 2×3 mm2 square, and in Corbino geometry samples (circular-shaped two-dimensional electron system confined by metallic contacts) with a large photoactive area (inner and outer radii of 500 µm and 1500 µm accordingly). In the case of the Corbino device, for the time resolved measurements an impedance matched detector circuit was used (time constant approximately 6 ns) and the p-Ge laser was driven by a special field-effect-transistor-based high power pulse generator, which provides very fast switching times (smaller than 20 ns). Meander structures Our recent works showed that the phoconductivity in QHS is a complex of different mechanisms [5,6]. From time-resolved measurements w
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