Photon-Semiconductor Nanowire Interactions via Metallic Nanoparticles

DoctorA lot of research is performed as a composition of photonics using the advantages of nanowires. With photonics research using nanowires, complex structures can be easily formed, which is not available with conventional method. For example, observation of the optical properties from the fabrication of nanowires of p-n junction structure, observation of detection of light adjusting doping materials from the direction of diameter, the realization of device which detects plasmon electrically, and so forth. These researches were performed as the single nanowire level. Here, in this thesis I will describe the study on Si and Ge nanowire photodector. In the first chapter, the syntheses of single crystalline Si and Ge nanowires by the Au catalyst-assisted chemical vapor deposition using SiH4 and GeH4 will be introduced. The standard method of growing the nanowires is the vapor-liquid-solid (VLS) growth mechanism. This method is simple and has an advantage of getting single crystal in the lower temperature if they have a catalyst material which can promote the nanowire growth. For the nanowire growth, adjusting the size of catalyst can tune the nanowire diameter, and changing the reaction gases can cause the adjustment of alteration of growth materials. The second chapter describes experimental methods for device fabrication using Ge nanowires. The fabrication of the device which uses nanowires as channel is essential to analyze the optical, electrical properties of grown nanowires. In the previous chapter, we show the demonstration of Ge nanowire field effect transistor. In third chapter, based on the previously mentioned techniques, we will demonstrate the fabrication and investigation of the Si nanowire field effect transistor and photodetector. Electrical properties of fabricated nanowires on the above-mentioned method were measured through the manually constituted set- up which the noise level is lower than 2 pA. To analyse the photoelectric conversion properties of semiconductor nanowires, the lab-made scanning photocurrent measurement set-up was used. With this method, the locally focused laser was illuminated at the specific nanowire, and the photocurrent according to the position of nanowire was observed while moving substrate minutely, using piezo-stage. The fourth chapter describes the study on diffusion of photogenerated carriers in semiconductors. Diffusion of photogenerated carriers in semiconductors is a basis to understand the operation of photodiodes and photovoltaic cells, and the length scale of carrier diffusion often determines their performances. Here we will report a direct observation of photocarrier diffusion in intrinsic Ge nanowires, by a scanning photocurrent microscopy technique. In final chapter, I will discuss influence of metal nanoparticles on the photocurrent of Si nanowires. Au, Ag nanoparticles generate plasmon resonance at certain visible wavelength, which results in the collection of light which is the similar function of antenna. So, we will analyse the photocurrent change of Si nanowire photodetector with dispersing Au and Ag nanoparticles