Study On Hot-Electron Photodetection Of Multilayer Micro-Nano Grating Structure

Hot-electron photodetectors are drawing increasing interests due to the capability in below-bandgap detection,high tunability of working wavelength,compact size,and room-temperature operation.The interaction between light and matter can be enhanced by exciting surface plasmons in metal nanostructures,thus the generation rate of hot electron in metals can be enhanced.In addition,bulk metal layer lead to a severe hot-electron thermalization loss and a low hot-electron transport efficiency.In order to solve the problem of the polarization dependence of the device on light and the low collection efficiency of hot dectron,the hot-electron photodetectors based on multilayer metal grating and whispering gallary mode are proposed to realize the highly efficient hot-electron conversion.The main contents of this paper are as follows:First,the basic principles of hot-electron generation,transport and collection are introduced in detail.The processes of hot-electron generation,transport and collection are presented by introducing the calculation results of the first-principle models.Then the theoretical calculation method of electromagnetism and the formulas used in the process of hot-electron generation,transport and collection are given,which provide the theoretical research foundation for the subsequent researches.Second,according to the principle of guided-wave resonance,the thesis proposes a multilayer-grating double-junction hot-electron photodetector.Through exciting and optimally controlling the guided-wave modes in the multilayer-grating structure,we obtain the optical response that is insensitive to the polarization and wavelength of the incident light.A rigorous electrical simulation is performed for the hot-electron photodetectors based on multilayered metal gratings with addressing the optical absorption of metals,the spatial distribution of hot electrons,and the hot-electron transport and collection processes.The results show that the multi-layer grating system can achieve the polarization-insensitive optical absorption of up to 98%.The design of double Schottky junction improves the efficiency of hot-electron collection and the non-polarized light responsiveness of the device at the wavelength of 1470 nm can be about 1 mA/W.Third,a hot-electron photodetector based on the dielectric nanosphere array is proposed by combining the whispering-gallery mode(WGM)with the hot-electron harvesting process.In this paper,the mechanism of WGM excitation and regulation is studied in detail,and the spatial distribution of optical response and hot-electron generation rate are obtained.The results show that the high optical absorption and hot-electron generation can also be achieved in ultrathin metals.In addition,the ultrathin metal layer can reduce the thermal loss of hot electrons and improve the collection efficiency.Then,a strict electrical simulation model is established to analyze the photoelectric conversion process of the hot-electron devices and predict their electrical properties.Theoretical calculation shows that the response of the device at the wavelength of 974 nm can reach 6.2 mA/W.