Modifications of effective optical properties of a-Si:H/a-SiNx:H multilayers by means of multilayer design and sublayer thickness

This paper presents a study of optical properties of two series of PECVD deposited planar a-Si:H/a-SiNx:H multilayers that are differently arranged. The first series design is symmetric consisting of samples with equidistant a-Si:H and a-SiNx:H sublayers of increasing thickness. In the second asymmetric series the thickness of a-SiNx:H sublayers remains constant and the thickness of a-Si:H sublayers changes to represent materials with changing a-Si:H/a-SiNx:H content ratio. From transmittance measurements refractive indices, absorption coefficients and optical band gaps were extracted and compared. The importance of the knowledge of wavelength-dependent refractive indices and absorption coefficients was demonstrated in the calculations of the absorptance under the Yablonovitch limit and of total relative absorbed solar energy. The total absorbed solar energy was commented with respect to a specific multilayer design