Electrical properties of surface-modified silicon nanomembranes.

摘要

Silicon-on-insulator (SOI), a silicon template layer on top of silicon dioxide, has several advantages over conventional bulk silicon, such as reduced junction capacitance and restrained short channel effect. When the silicon film becomes very thin, the surface states and the interface states modify the conductivity and dominate due to bulk charge carriers. Therefore, measurements based on the electrical transport properties will be very sensitive to the surface and interface states, which implies surface-modified silicon nanomembranes could be promising biosensors. Surface functionalization and sensitivity are the most important factors in the development of microarrays and biosensors. We investigate a cold plasma process for surface functionalization and study the electrical properties of surface-modified silicon nanomembranes as a preliminary work toward biosensor application.;H-termination of the silicon nanomembranes is studied as the simplest surface modification. When the Si (100) surface is terminated by hydrogen, the H-terminated Si (100) surface is very conductive and the sheet resistance measured using the van der Pauw method is 3 to 4 orders of magnitude lower than that of oxide termination. The extended work is conducted for a wide range of film thicknesses, exhibiting the dependence of the interplay of the surface states and the bulk states on the film thickness. X-ray photoelectron spectroscopy (XPS) is also employed to investigate the Fermi level pinning caused by the H-termination. We also study a similar electrical transport property of epichlorohydrin-modified silicon membranes.;Ultrathin silicon-on-insulator (UTSOI) at typical doping levels (10 15 cm-3) is easily depleted by interface traps. These detrimental interface trap states can be passivated by annealing using hydrogen or forming gas. Our work shows that the interface trap density can be reduced by an annealing process, and the corresponding reduction in the sheet resistance relies on the film thickness. A numerical calculation is provided to find the interface trap density by fitting the experimental sheet resistance data.;We provide the prospects of UTSOI biosensors using the electrical transport properties studied in this work as well as demonstrate another useful surface functionalization procedure in an effort to form necessary chemical linkers to which biomolecules can be attached.