Recently, we have proposed a cyclic method, referred to as Closed Chamber CVD (CC-CVD), for the preparation of μc-Si films of high crystalline fraction at increased deposition rates. In this work we first report new process conditions of CC-CVD, which result in growth of highly crystalline films with a sharp interface on a foreign substrate. Then these conditions are further used together with a pulsed injection of B2H6 in an appropriate moment of each cycle, so that the disturbance of the crystallization process is prevented. A series of ultrathin μc-Si films, doped by this technique, is characterized by conductivity measurements, SEM, Raman Scattering, optical transmission and UV reflection. A strong reduction of the transient interface layer is achieved and conductivity as high as 2 S/cm <p-type> with an activation energy of 27 meV is reached.