Although the presence of hydrogen is necessary to obtain a good quality amorphous silicon, the silicon matrix still remains incomprehensible. A series of crystalline silicon clusters are built with hydrogen saturating dangling bonds on the surf ace. It is found that only two types of hydrogen-rela ted groups (Si-H and Si-H2) are necessary. Furthermore, we have calculated their stretching vibrational frequences using the improved method. The results are consistent very well with conventionally obtained spectra including Si-H at 2000cm-1 and Si-H2 at 2100cm-1 peaks.These interesting results propose a structure model of the a-Si:H, which is neither CRN nor microcrystal, but a largely concentrated silane-like “molecule”. This model may be used to understand the proposed doping mechanism of a-Si:H alloys. Although the presence of hydrogen is necessary to obtain a good quality amorphous silicon, the silicon matrix still remains incomprehensible. A series of crystalline silicon clusters are built with hydrogen saturating dangling bonds on the surf ace. It is found that only two types of hydrogen- The results are consistently very well with conventionally obtained spectra including Si-H at 2000cm-1 and Si- H2 at 2100 cm-1 peaks.These interesting results propose a structure model of the a-Si: H, which is neither CRN nor microcrystal, but a substantial concentrated silane-like “molecule”. This model may be used to understand the proposed doping mechanism of a-Si: H alloys.