p-Type hydrogenated amorphous silicon (a-Si:H) was deposited on n-type crystalline silicon (c-Si) substrates to obtain hetero-junction diodes. Additionally, a thin intrinsic a-Si:H layer was inserted between both the p-type film and the n-type substrate to study its passivation effect on the c-Si surface. The amorphous films were obtained by the hot wire chemical vapor deposition (HWCVD) technique, using a tungsten filament and silane (SiH(4)), hydrogen (H(2)) and diborane (B(2)H(6)) gases, where the deposition parameters such as gas flow, substrate temperature and filament temperature were varied. Optical band gap, deposition rate and conductivity were measured for all the films. We studied the influence of the quality of the amorphous films upon the performance of the hetero-junction diodes. In particular, the diode ideality factor (n) and the saturation current density (J(0)) were determined by measuring the current-voltage characteristics in dark conditions. It is shown that the presence of the intrinsic layer is fundamental for making good diodes, since devices made without this film cause the diodes to have high saturation current density and ideality factor (J(o) > 10 x 10(-6) A/cm(2), n > 4) as compared to diodes with a good intrinsic layer (J(0)=5 x 10(-9) A/cm(2), n=1.39). The results obtained are encouraging, but the quality of the intrinsic films still should be improved for applying them to HIT solar cells. (C) 2010 Elsevier B.V. All rights reserved.