Study on Ultra Wideband Spectral Response and Efficient Hot Electron Detection using Plasmon Field Effect Transisto

Surface plasmon, collective charge density oscillation of conduction electrons in a nanostructured metal, has attracted considerable attention due to their unique optical properties in the past decade. Plasmonics is the study of the interactions between light and metals, to be specific between the electromagnetic field and free electrons in metals. Plasmonics devices possess the advantages of both electronic devices and optical devices for tackling important issues such as operating speed and integration capability. Thus, plasmonics has been an important research area rapidly impacting every facet of optics and photonics.;We reported a new device structure named a plasmon field effect transistor based on a thin film transistor device with a metal nanostructure incorporated in it. Plasmon-induced hot electrons can overcome the Schottky barrier between the thin film and the metal because they have enough kinetic energy. The plasmon-induced hot electrons transferred from the nanostructured metal to the semiconductor improve drain current due to the increased conductivity of the electron channel generated at the bottom of the semiconductor or the hot electrons transported to the electron channel. We have observed a promising quantum tunneling based hot electron detection and an internal field (gate bias) assisted hot electron collection. These are the key working principles to extend the detection wavelength up to far IR frequency using the plasmon field effect transistor.;The objective of this research is to explore the behind physics that enables the efficient collection of plasmonically induced hot electrons and study on ultra wideband spectral response through quantum tunneling for low energy hot electrons from a variety of metal nanostructures using the plasmon field effect transistor. We investigated the efficiency of the plasmon field effect transistor with the different position of plasmonic nanostructured metal on the semiconductor, which either fabricates the nanostructures close to the Source or fabricates them close to the Drain. The position close to the source has a more spectral response than the position close to the drain that means device design should be considered to increase the efficiency of hot electron collection because the gradient of electric field seen by induced hot electrons varies depending on the distance between drain and source.;We studied on the substrates where the gold nanoparticles are self-assembled and the different gold film thicknesses, annealing time, and temperature for a thermal reflow method. The scanning electron microscope images of the gold nanostructure show that the size distribution and density of the gold NPs varied depending on the gold film thickness. Self-assembled gold nanostructures using the thermal reflow method and their spectral response including the efficiency are influenced by the temperature, the annealing time, the film thickness and the surface profile of the substrate. We also found that the shape and size of gold nanostructures are strongly related with the surface roughness. We will increase the ratio of the channel length and width (W/L) to maximize its plasmon energy detection with lowered operating voltage.;Our study will provide important information about the optimized device structure that enables maximized use of the generated hot electrons through the plasmonic absorption. The expected plasmonic absorber structures are few hundreds of nanometers for the IR absorption. To fabricate the gold nanostructures for the tailored plasmonic absorption, we used an electron beam lithography (EBL) method. We will change the metal, surrounding material, metal thickness, metal size, and metal shape to increase the plasmonic absorption peak. We will also focus on maximizing hot electron tunneling for the low energy photon detection. The research will facilitate the successful development of next-generation plasmonic electronics and will lead to the development of low-cost imaging device that has a detection limit up to THz frequency for many military and security applications.