Investigation On Performances Of Single-Photon Detectors Based On The Micro-Nano Structure

Single-photon detection technology, which is the core of application and research in the area of weak signal detections, is playing a key role in quantum information, physics, biology, chemistry, astronomy and other fields. As the technology is developing and the application demand is rising continuously, the Single-photon detectors,which have the characteristics of low jitter, fast count rate, low dark count rate, and can be sensitivity in the visible and infrared wavelengths, have become the research focus. This thesis includes two main parts:Firstly, a structural and numerical model of the superconducting single-photon detectors(SSPD) based on the theory of superconducting critical current density is introduced. To investigate the SSPD fabricated on niobium nitride thin films, we analyze quasiparticle concentration versus time and space, influences of time and photon energy on size of "hot spot", film response voltage based on quasiparticle concentration diffusion equation, from the aspects of response time, size of "hot spot", film resistance and so on. A detailed discussion on the principle of "hot spot" response and single-photon detection is presented.Secondly, the basic principle of the quantum-dot infrared detector(QDIP) is introduced and a structural model of QDIP based on the large size of quantum dot(QD) is analyzed. To optimize the performance of QDIP, influences of internal structure parameters and external environmental parameters on the detectivity are investigated. As the external parameters, detectivity decreases when temperature increases and there will be a peak value as voltage increases under a certain doping ratio. And among the structure parameters, QD arrays spacing will have little effect on the detectivity when it reaches a certain range. Increasing of the number of QD layers will be helpful to improve the detectivity, but too many layers will be restricted by the fabricated technology and lead to the degradation of the quality due to the accumulation of internal strain. In a certain range, enlarging the size of QDs will a way to increase the detectivity, however, it will reduce the QD sheet density in a QD layer, low QD sheet density in one way can restrict the detectivity directly and in another way it will lead a deterioration of the detectivity by affecting the doping level. So properly selecting the parameters will play a key role in improving the performance of the realistic detectors.