Growth and characterization of hydrogenated amorphous silicon thin films from SiH2 radical precursor: Atomic-scale analysis

Abstract

Molecular-dynamics (MD) simulations of hydrogenated amorphous silicon (a-Si:H) film growth on an initially H-terminated Si(001)-(2×1) substrate at T=500 K was studied through repeated impingement of SiH2 radicals to elucidate the effects of this species on the structural quality of the deposited films. A detailed analysis of the radical–surface interaction trajectories revealed the important reactions contributing to film growth. These reactions include (i) adsorption of SiH2 onto the deposition surface, (ii) insertion of SiH2 into surface Si–Si bonds, (iii) surface dimerization of adsorbed SiH2 groups, (iv) formation of polysilane chains and islands, (SiH2)n, n⩾2, on the surface, (v) formation of higher surface hydrides through the exchange of hydrogen, and (vi) dangling-bond-mediated dissociation of surface hydrides. The MD simulations of a-Si:H film growth predict an overall surface reaction probability of 39% for the SiH2 radical. Structural and chemical characterization of the deposited films was carried out through a detailed analysis of the evolution of the structure of the film, surface morphology, and roughness, surface reactivity, and surface composition. The analysis revealed that the deposited films exhibit a high concentration of H and columnar surface morphologies. In particular, islands or polysilane chains form on the growth surface and are believed to be responsible for the columnar structural features in the deposited film. Such polysilane chain formation may have significant effects on the structural, morphological, and optical properties of the a-Si:H films.