Conductivity of boron-implanted polycrystalline thin silicon films

Abstract

Sub-micron thin films of polycrystalline silicon obtained by low-pressure chemical vapor deposition, boron-implanted (amount varying from 1012 to 1016 cm−2), and annealed at 760 °C for 26 h under an oxygen ambient (dry O2) have been characterized in terms of structural and electrical properties. The results obtained are correlated first with the Hall-effect measurements, which gives the resistivity p, the concentration of the free carriers p and the mobility μ, and in the second part with the observations of transmission electron microscopy (TEM), which gives the size of grains. The variations of p, p and μ have been studied as a function of the dopant concentration. A low rate of activation has been measured (40%) and a very low value of the mobility μ has been noted (3 cm2 V−1 s−1) as well as small grain size. These results have been discussed both qualitatively and quantitatively, based on the existence of phenomena of carrier trapping and dopant segregation at the grain boundaries.