Ultrahigh-sensitivity far infrared photodetectors by using the quantum Hall effect

When a two-dimensional electron system(2DES)is subjected to a strong magnetic field at low temperatures，the motion of electrons are completely quantized by cyclotron motion and O-dimensional like，equi-distant energy levels(Landau Levels)are formed。In such a situation，a novel phenomenon called the quantum Hall effect appears.Although the quantum Hall effect(QHE)is most often applied to resistance standards，we are pursuing a possibility of using QHE for the detection of far infrared radiation(Or Sometimes Called Terahertz Radiation)。The major results of this project are；(1)We have found that the diagonal resistance of the 2DES exhibits a very large photosensitivity in the vicinity of the quantum Hall states。From the analysis of the excitation spectra，it is clarified that the photosensitivity is induced by the cyclotron resonance absorption and that there are two mechanisms in the process，i.e.，(I)electron heating due to photoabsorption and(Ii)modulation of edge chtransannel port through potential redistribution by spatial separation of photoexcited electron and holes.(2)The ressivity of the Qdetector inases linly with by spatial separation of photoexcited electron and holes.Further increase of the bias current results in the reduction in responsivity due to joule heating.(3)We have found that the dominant noise of the QHE detector is the 1/f noise and that it increases very quickly with increasing the bias current.Consequently，the maximum detectivity was obtained at relatively low bias currents(-µA).(4)The overall detectivity of the QHE photodetector was estimated to be3x10西伊D113西耶D1 Hz西伊D11/2齐埃D1 cm/W，which is approximately50times larger than that of conventional bolometers.This high detectivity indicates the superiority of the QHE photodetector as a ultirahigh-sensitivity far infrared photodetector.

When a two-dimensional electron system (2DES) is subjected to a strong magnetic field at low temperatures, the motion of electrons are completely quantized by cyclotron motion and O-dimensional like, equi-distant energy levels (Landau levels) are formed. In such a situation, a novel phenomenon called the quantum Hall effect appears. Although the quantum Hall effect (QHE) is most often applied to resistance standards, we are pursuing a possibility of using QHE for the detection of far infrared radiation (or sometimes called terahertz radiation). The major results of this project are ;(1) We have found that the diagonal resistance of the 2DES exhibits a very large photosensitivity in the vicinity of the quantum Hall states. From the analysis of the excitation spectra, it is clarified that the photosensitivity is induced by the cyclotron resonance absorption and that there are two mechanisms in the process, i. e., (i) electron heating due to photoabsorption and (ii) modulation of edge channel transport through potential redistribution by spatial separation of photoexcited electron and holes.(2) The responsivity of the QHE detector increases linearly with increasing the bias current and reaches 10ィイD17ィエD1 V/W, which is 1000 times larger than that of conventional bolometers. Further increase of the bias current results in the reduction in responsivity due to joule heating.(3) We have found that the dominant noise of the QHE detector is the 1/f noise and that it increases very quickly with increasing the bias current. Consequently, the maximum detectivity was obtained at relatively low bias currents (-μA).(4) The overall detectivity of the QHE photodetector was estimated to be 3x10ィイD113ィエD1 HzィイD11/2ィエD1cm/W, which is approximately 50 times larger than that of conventional bolometers. This high detectivity indicates the superiority of the QHE photodetector as a ultirahigh-sensitivity far infrared photodetector.