Nanostructural and PL Features of nc-Si:H Thin Films Prepared by PECVD Techniques

Abstract

Hydrogenated amorphous silicon (a-Si:H) has attracted much attention in various electronics applications such as thin films transistors, color sensors, and solar cells[1]. However, many devices made from a-S:H are observed to degrade with time, which is commonly associated with hydrogen related defects [1]. It has been observed that, by increasing the hydrogen dilution in the precursor gas used in the plasma, one can obtain hydrogenated nanocrystalline silicon (nc-Si:H), which contains crystalline grains embedded in an amorphous silicon matrix. These materials can be deposited by plasma enhanced chemical vapor deposition (PECVD) techniques. The presence of nc- Si in a-Si:H changes the optical and electronic properties of the material [2]. Nc-Si:H thin films have exhibited unique and useful characteristics. In particular, nc-Si:H thin films exhibit photoluminescence (PL) and electroluminescence (EL) behavior at room temperature [3]. The dilution of SiH4 with hydrogen has been recognized as an effective method for the transition from the amorphous to the nanocrystalline phase in the nc-Si:H thin films. The presence of hydrogen on the growing surface gives termination of dangling bonds and also an extraction of SiH3 radicals [4]. The supply balance between the hydrogen and SiH3 radicals is a key factor in determining the film structure [4]. The presence of excess hydrogen or hydrogen-bonded Si radicals (SiHn = 1, 2, 3) in the gas mixture passivates the dangling bonds on the growing surface and etches the growing surface. Etching eliminates part of the disordered structure and enhances the crystalline phase because the crystalline structure is the lowest energy configuration. In this paper, we report the study of the effects of the hydrogen species on the nanostructures and optical properties of nc-Si:H thin films prepared by PECVD techniques