Hydrogenated nano-amorphous silicon (na-Si:H) films, due to their high absorption coefficient (α≈10~5) like amorphous silicon, wide optical bandgap (E_(opt)≈1.8-2.0eV) like crystalline silicon, and high stability under illumination, have been widely studied in the recent years for their potential applications in solar cells.Under the preparing conditions of low silane concentration f=SiH_4/(SiH_4+H_2)≤3% (a mixture of silane highly diluted in hydrogen), RF power density p=591mW/cm~2, substrate temperature T_s=200℃, pressure P=1.1Torr, intrinsic na-Si:H films were grown by plasma enhanced chemical vapor deposition (PECVD). The effects of the silane concentration on the structural, optical and electrical properties of intrinsic na-Si:H films have been systematically investigated. The mechanism of the formation of nano-sized silicon crystallite was discussed. In addition to the intrinsic na-Si:H films, b-doped p-type na-Si:H films were prepared using borane (B_2H_6) also by PECVD. The influence of borane concentration r=B_2H_6/(B_2H_6+SiH_4), T_s, ρ, and P on structural, optical, electrical properties and deposition rate 5 were also studied in this paper.The structure of the deposited na-Si:H film was studied by means of X-ray-diffraction pattern (XRD), Raman scattering spectra (Raman), and high-resolution electron microscopy (HRTEM). The results show that na-Si:H films consist of mixed phase of nano-sized silicon crystallites (4-10nm) embedded in amorphous matrix, with a preferential growth in the orientation of (220), crystalline volume fraction X_c gives the value of 10-40%. For f≥4% samples do not have a detectable crystallization and appear essentially amorphous.The chemical bonding analysis had been performed by FTIR transmission measurements. It exhibits that as the f decreases, 630cm~(-1) 2000cm~(-1) peaks shift to 610cm~(-1) 2100cm~(-1), respectively, indicating of the transformation of stretching vibrations mode of SiH and SiH_2 into SiH_2 and SiH_3, and the hydrogen content C_H also decreases from 8% to 2%.As regards of optical properties, the absorption coefficient a and optical band gap E_(opt) were derived from ultraviolet-visible transmission spectra. The films show an enhancement of optical absorption from 10~0 to 10~2cm~(-1) in the near infrared region, whereas in the visible region the absorption is lower than that of a-Si:H. The E_(opt) of na-Si:H is much wider (1.85-1.94) than that of crystalline silicon (1.12eV) and amorphous silicon (1.5-1.8eV) due to the quantum confinement effect.The photo/dark electrical conductivity, σ_(ph)/σ_d, was measured by means of an home-made instrument (100mW/cm~2, R.T.). It shows that the conductivity activation energy E_a of na-Si:H approaches 0.40eV, much smaller than that of a-Si:H (0.72eV). The dark conductivity reaches 10~(-5)Ω~(-1)cm~(-1), larger than that of a-Si:H by five orders of magnitude. No obvious Staebler-Wronski effect was detected during extended light soaking (σ_(ph)/σ_d decreased less than 10%). A two-phase model has been used to discuss the relation between electrical properties and microstructures.The film thickness was derived from the Surface Profiler and cross-section SEM. It is estimated that the deposition rate 8 of na-Si:H film is less than 1 A/s, much slower than that of a-Si:H (5-10 A/s).The results of investigation of boron-doped na-Si:H films show that boron light-doping enhances the crystalline degree comparing with intrinsic na-Si:H films, (220) preferred orientation growth, crystalline degree improves as f increases. The hydrogen content C_H in B-doped na-Si:H films are much smaller than those in intrinsic na-Si:H films for B atoms partly replaced H atoms which bonding to Si atoms initially. Boron doping also makes σ_(ph)/σ_d rapidly decrease from 10~3 to 10 as the borane concentration increases.Optical band gap E_(opt) of na-Si:H will be enhanced by boron doping to reach approximately 2.0eV, σ_d of Boron-doped na-Si:H (10~(-8)-10~(-3)Ω~(-1)cm~(-1)) is larger than that of a-Si:H by 2~3 orders of magnitude, and can be controlled by adjusting boron concentration.In this work, we find that SiH_4/(SiH_4+H_2)=3%, B_2H_6/(SiH_4+B_2H_6)=5 × 10~(-4), T_s=150℃, p=200mW/cm~2 and P=0.8Torr are the optimum preparation parameters to obtain B-doped na-Si:H films with high electrical conductivity and wide band gap.As we can see, na-Si:H is likely going to be an ideal new-type intrinsic absorption layer material for thin film solar cells for it"s high light absorption, good electrical conductivity and high stability under illumination. Since the boron light-doping na-Si:H has a wide optical bandgap comparable to that of a-SiC:H (2.04eV), it is possible to replace the a-SiC:H to be used as the window layer material for silicon film solar cells.