Thickness-Dependant Electrical Characteristics of Nitrogen-Doped Polycrystalline 3C-SiC Thin Films Deposited by LPCVD

Abstract

AbstractThe effect of film thickness on the electrical resistivity of heavily-nitrogen-doped polycrystalline SiC (poly-SiC) thin films is investigated. The resistivity of poly-SiC thin films decreases by a factor of ˜7 for thickness increasing from 100 nm-thick to 1.78 μm-thick; the resistivity begins to stabilize as thickness approaches 1 μm. The increased resistivity for the thinner films is shown to be related to the grain boundary effect. Secondary ion mass spectrometry indicates a nitrogen concentration of 9×1020 atoms/cm3 in the films. However, Hall measurements reveal that only 45% of the dopants are electrically active in the 100 nm-thick film. The percentage of active dopants rises to 80% when film thickness increases to 680 nm. From the studies of surface roughness and microstructure, it is seen that small grains are formed at the initial stage of deposition, which then grow into larger columnar grains as film thickness increases. The presence of a large density of grain boundaries and limited grain growth for the very thin films contribute to increased electrical resistivity from increased trapped mobile carriers and reduced carrier mobility. The free carrier trapping phenomenon can further be observed in the temperature-dependence of resistance measurement.