A novel photon detector made of silicon and carbon nanotubes

Abstract

The use of silicon and the development of micro-technology made possible the transition from macro- to micro-detection systems and of very large-scale integration systems for microelectronics. The most powerful micro-detector recently developed is the Silicon PhotoMultiplier (SiPM) that allows a pixel dimension of microns in a hundred-pixel array. The use of nanotechnology opens now a new field of applications in which materials are “built” chemically up to the desired dimensions. This process allows the realization of complex structures that have finely pixelled sub-micron dimensions and that are cheap, light, and easy to produce. Between the materials suitable for nanotechnology, carbon nanotubes (CNT) play a main role because of their facility of being produced and their unique mechanical and electrical properties. They can be grown chemically in a very easy and cheap way, assembled in the desired geometry and directly connected to readout electronics devices. In addition, they can be coupled to silicon substrates to obtain mixed micro–nano structures with intermediate electronic properties. The first radiation detector using CNTs grown through a chemical vapour deposition (CVD) process has been realized using a sapphire substrate. This device, sensitive to the radiation in the range from 220 to more than 850 nm, exhibits a relevant increase in the photocurrent toward UV wavelengths both with continuous light and with pulsed radiation. This opens the door to the realization of a new kind of low-cost radiation detector with sub-micron spatial resolution and high sensitivity in the UV radiation region. In order to avoid the large dark current observed, a new detector has been realized using an p-doped silicon substrate. Electrical and optical properties of this novel detector have been intensively studied as well as the coupling between nanotubes and silicon. The strong matching found between the two different materials suggests the possibility of realizing a single photon detector with high quantum efficiency in the UV wavelength region.