Metodi innovativi per la realizzazione di migliori photodetector a base di nanotubi di carbonio e silicio.

Different approaches to make carbon nanotube-silicon heterojunctions have been studied. Starting from prefabricated silicon substrates, composed of an n-type silicon wafer with a silicon nitride top layer and a metallic back, the heterojunctions have been made by different approaches. Initially by direct growth of the nanotubes over the nitride layer by means of chemical vapor deposition (CVD) and then by the deposition of carbon nanotube films using a transfer printing method. The morphology, chemical composition and structure of the nano-tube films obtained with the different techniques have been characterized by means of scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS) and Raman spectroscopy. The electrical response of the vertical heterostructures (CNT-Si3N4-n-type Si) has been deeply investigated, both as a function of the impinging light power and the light wavelength. The properties of the photodetectors such as responsivity (R) and External Quantum Efficiency (E.Q.E.) have been studied. Temperature dependence of the diode parameters such as on/off ratio, Schottky barrier height, ideality factor and series resistance have been performed on some of the devices and compared to that of silver-silicon heterostructure made by the deposition of Ag conductive paste above one of the substrates. Photo-response maps of the devices allowed us to correlate the morphological properties of the nanotube film and the thickness of the nitride layer to the electrical behaviours of the devices. To exploit these behaviours several techniques have been developed to easily tune the nanotube film's mor-phology and the nitride layer's thickness to obtain devices with improved efficiency and additional function.