Outstanding passivation properties for p-type crystalline silicon surfaces were obtained by using very thin n-type microcrystalline silicon (mu c-Si) layers with a controlled interface structure, The n-type Ctc-Si layers were deposited by the RF PE-CVD method with an insertion of an ultra-thin oxide (UTO) layer or an n-type amorphous silicon (a-Si:H) interface layer. The effective surface recombination velocity (SRV) obtained was very small and comparable to that obtained using thermal oxides prepared at 1000 degrees C, The structural studies by HRTEM and Raman measurements suggest that the presence of UTO produces avery thin a-Si:H layer under the mu c-Si. A crystal lattice discontinuity caused by these interface layers is the key to a small SRV.