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

Abstract

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.

Optical Absorption in Si:H Thin Films: Revisiting the Role of the Refractive Index and the Absorption Coefficient

“…This concept is based on increased optical path length in comparison with the actual absorber thickness. Main strategies to achieve increased absorption due to light trapping are anti-reflection coatings, incoherent light trapping (random scattering inside the absorber or at interfaces that is usually achieved by special patterning), and coherent light trapping in thin films or thin film stacks [10][11][12][13][14][15]. The role of microstructure, i.e., nanocrystalline features inside the thin films, has been frequently studied as playing an important role in the light absorption, e.g., for photodetection [16,17].…”