Microstructural Studies of Non-Crystalline Solid Silicon Films by TO-Like Modes of Raman Spectra

Several microstructural parameters can be obtained from the HWHM (half width at half maximum) Γ of the TO-like mode and the peak positions in the Raman spectra of non-crystalline silicon materials (including multilayer and single thick films). These are the rms bond angle variation Δθ = (Γ − 7.5)/3 (deg) [1], the average distortion energy per bond (u) of the interface, and the stress near the interface (s̀), in a-Si: H layers. The grain size of the m̈c-Si films can be also obtained from Δd ∼ 2π(B/ΔωTO)1/2 [2]. The distortion energy is given by U = 3K(r{article}{empty}{document}Δ θ ̄{document})2, where K and r are the force constant of Si (9.2 x 103 dyn/cm2) and the bond length of Si (2.4 x 10−8 cm) [3], respectively, s̀ is equal to n x ΔU, n is the total number of distorted Si-Si bonds per unit area near the interface, and ΔU is the average excess distortion energy. The microstructural parameters of thick single m̈c-Si: B films and different composition-modulated superlattices are compared when the following quantities are changed: (1) ds (thickness of the a-Si: H layer), (2) R (the NH3/SiH4 ratio). The microstructures can well be understood after proper theoretical models are adopted, i.e., using the Peierls-Nabarro model, it can be explained that the stress near the interface is inversely proportional to the thickness of the a-Si:H layer (ds) within the range of a few monolayers. The Pantelides model can be used to explain the overcoordination of nitrogen in the a-Si: H layer near the interface.