Sub-micron thin films of polycrystalline silicon obtained by low-pressure chemical vapor deposition, boron-implanted (amount varying from 10(12) to 10(16) cm(-2)), and annealed at 760 degrees C for 26 h under an oxygen ambient (dry O-2) have been characterized in terms of structural and electrical properties. The results obtained are correlated first with the Wall-effect measurements, which gives the resistivity rho, the concentration of the free carriers p and the mobility mu, and in the second part with the observations of transmission electron microscopy (TEM), which gives the size of grains. The variations of rho, p and mu 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 mu has been noted (3 cm(2) 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.