Noise characterization of nanoelectronic devices

In recent years, noise characterization has emerged as an extraordinarily powerful tool to investigate aspects of transport phenomena at a very basic level. Through noise it is possible to obtain information about the structure and the transport properties of nanoscale devices that are complementary to those given by the DC characteristics and the small signal AC response. Time-dependent fluctuations in the measured current due to the granularity of charge lead to the so-called shot noise. Such statistical fluctuations show up much stronger in nanosize electronic devices, compared to macroscopic classical devices, due to the small number of electrons involved in device operation. The experimental challenge in the measurement of shot noise consists of the elimination of other sources of noise, such as thermal noise and low frequency 1/f noise due both to the device under test and to the external environment. In such measurements on semiconductor devices, it is generally very difficult to detect in a direct way noise levels associated with bias currents below a few hundred picoamperes. This is due to the fact that noise power spectral densities, corresponding to such current levels, are of the same order of magnitude or much lower than those which are characteristic of common low noise amplifiers. To overcome this problem, many techniques for reducing the noise of the measurement system have been implemented, as described in this thesis.