Optical characterization of hydrogenated amorphous silicon thin films deposited at high rate
- 554 Downloads
The aim of this paper is to provide a better understanding of hydrogenated amorphous silicon thin films (a-Si:H) in relation to their optical properties: refractive index, optical gap, absorption coefficient, thickness and surface roughness. The transmission spectrum of the films, deposited with various rf discharge power densities by an optimized plasma enhanced chemical vapor deposition (PECVD) method, at a high rate (>10 Å/sec), was measured over a range in wavelength from 500 to 1100 nm. An approximate model is utilized to describe the surface roughness. In this model, the surface roughness is modeled as a mixed layer of 50 percent of a-Si:H and 50 percent of air and the optical constant of the rough layer is derived using the Bruggemann effective medium approximation (EMA). The gradient iteration method of numerical analysis is used to solve the nonlinear equations in the study. Our results show that the potential underestimation of refractive index and resulting overestimation of film thickness can be overcome by considering the reflection of the rough surface. The method is carried out on the transmission data and the influence of rf discharge power density on the properties of the film is discussed in detail.
Key wordsHydrogenated amorphous silicon thin film PECVD surface roughness absorption coefficient transmission EMA
Unable to display preview. Download preview PDF.
- 1.J.A. Schmidt and F. A. Rubinelli, J. Appl. Phys. 83, 340 (1998).Google Scholar
- 8.W. Hu, Florence Y.M. Chan, D.P. Webb, Y.C. Chan, and Y.W. Lam, J. Electron. Mater. 25, 1837 (1996).Google Scholar
- 11.J. Tauc, Optical Properties of Solids, ed. F. Abeles (Amsterdam, The Netherlands: North-Holland Publishers, 1970).Google Scholar
- 12.Xuanyin Lin, Kuixun Lin, Yunpeng Yu, Y.W. Lam, Y.C. Chan, S.H. Lin, and Y.M. Chan, IEEE First WCPEC (New York: IEEE, 1994), p. 638.Google Scholar
- 14.Florence Y.M. Chan, Y.W. Lam, Y.C. Chan, S.H. Lin, W.S. Lau, and S.J. Chau, MRS Symp. A, Proc., Spring Meeting (Pittsburgh, PA: MRS, 1996).Google Scholar
- 15.S.H. Lin, Y.C. Chan, D.P. Webb, and Y.W. Lam, IUMRS-ICAM. Symp. M (Beijing, China, June 1999).Google Scholar