Subwavelength Approach of Light Propagation Through Porous Semiconductors

Abstract

Porous semiconductors with pore sizes below the wavelength of the light offers the opportunity to “engineer” the refractive index at the visible and the IR spectral range by variations of the porosity of the layer. This property can be utilized in a number of optical components [1–3] that will be reviewed later in this book. Note that the luminescence properties of microporous silicon [4] will not be considered here. A lot of research has been dedicated previously to this particular optical use of porous Si and less to other semiconductor materials. This chapter of the book is devoted to the description of the subwavelength mode of light propagation through porous semiconductors, where the porous semiconductors optically can be considered as effective media. The emphasis is placed on a description of different models, connecting the expected optical properties of porous semiconductors with pore morphology and geometry. Good understanding of the properties of porous semiconductors is essential for two reasons: First, it is necessary for accurate design of mesoporous silicon filters that will be reviewed in Chapter 6. Second, it provides the way for simple and relatively fast identification of some parameters of the morphology of porous semiconductor layers without the need of otherwise inevitable TEM imaging. Review of isotropic effective medium approaches will be given first in this chapter, followed by introduction of anisotropic effective medium models. Last, predictions of some unusual optical properties of certain porous semiconductor materials will be given.