Ellipsometry andab initioapproaches to the refractive index of porous silicon

Abstract

Spectroscopic ellipsometry is used to determine the complex refractive index (n−ik), porosity, and thickness of porous silicon (PSi) films. These films are obtained by anodizing p-type crystalline silicon in a hydrofluoric acid bath. After etching, PSi samples are heated to 750 °C in a controlled oxygen environment. A detailed analysis of the ellipsometry data is performed in order to determine the complex refractive index of PSi thin film. This frequency dependence of n and k is compared with the results of ab initio quantum mechanical calculations carried out by means of CASTEP codes within the density functional theory. The theoretical results show a diminution of the lattice constant as the oxygen content grows, in contrast to the hydrogen-saturated surface case.

Oxygen Absorption in Free-Standing Porous Silicon: A Structural, Optical and Kinetic Analysis

“…The PSi samples used in this study were fabricated by means of an anodic electrochemical dissolution of boron-doped p + -type (100)-oriented c -Si wafers with an electrical resistivity of 0.01–0.03 Ω cm in an electrolyte consisting of a mixture of HF (49%) and ethanol (99.9%) with a volume ratio of 1:2 [ 15 ]. A gold film of 30 nm was deposited on the backside of c -Si wafers to ensure electrical conduction during the anodization.…”

Infrared Transmission in Porous Silicon Multilayers

“…In Figures 2(a) Observe that the applied current intensities were 88.5 mA for high-porosity layers A and 12.4 mA for low porosity layers B, with an etching area of 1.77 cm 2 . The applied voltages had different average value for each multilayer, which was caused by the spatial location of the platinum electrode [15]. Also, along each etching process there are voltage fluctuations for a given current value in order to maintain a constant current.…”

“…These fluctuations could be related to the presence of hydrogen bubbles in the electrolyte during the etching process [16]. In fact, these multilayers were fabricated using a peristaltic pump that recirculated the electrolyte at 100 mL/min, in order to remove such bubbles [15].…”

Optical properties of thick ordered mesoporous silica membranes

“…These parameters are used to extract the optical constants, composition, porosity, and thickness of porous materials [13]. Of the many models available, the Bruggemann model which uses Effective Medium Approximation (EMA) is considered ideal for porous materials when the wavelength of the incident light is much greater than the dimensions of the pores [9,14].…”