Conductance Fluctuations in Amorphous Silicon

9424277 Kakalios The principal aim of this research project is to elucidate and study the physical mechanisms underlying conductance fluctuations in hydrogenated amorphous silicon (a-Si:H). Previous studies of 1/f noise and random telegraph switching noise in a-Si:H in our laboratory suggest that the noise arises from inhomogeneous current filaments whose resistance varies in time, possibly due to the motion of bonded hydrogen inducing bonding rearrangements which alter the defect structure of the material. Amorphous silicon films will be synthesized in an rf plasma-enhanced chemical vapor deposition system at the University of Minnesota, for which the doping level and deposition conditions are systematically varied. The temperature and bias dependence of the random telegraph noise of these films will be investigated to determine if the switching noise arises from current microchannels. The non-Gaussian statistics which characterize 1/f noise will be investigated as the properties of the a-Si:H films are varied. Finally, the long-range disorder at the mobility edge will be characterized by comparing the difference between the thermopower and conductivity activation energies, and will be correlated with the noise behavior as well as with the optical and structural properties of these films. These efforts will significantly improve our understanding of the fluctuation phenomena in a-Si, a technologically important material. %%% Hydrogenated amorphous silicon (a-Si:H) is increasingly used in photovoltaic devices, input scanners, fax machines, photocopiers, and thin-film transistors for flat-panel displays. All of these require the large surface area advantages of amorphous semiconductors. As these electronic devices are made smaller, fundamental electrical noise in the amorphous silicon ultimately limits device performance. An understanding of the microscopic m echanisms responsible for the noise phenomena is therefore crucial if amorphous semiconductors are to achive their technological potential. The principal aim of this research project is to elucidate and study these mechanisms as the properties of the thin-film semiconductor are systematically varied. Previous studies of the electronic noise in hydrogenated amorphous silicon in our laboratory discovered that the noise itself exhibits time-dependent fluctuations, that is, the noise has noise! Studies of the noise of the noise provide important information concerning the degree of electronic disorder and long-range correlations in the material. This research will significantly advance our knowledge of fluctuation phenomena in amorphous silicon in particular, as well as improve our understanding of the physics of non-linear relaxation processes in disordered solids, in general. ***