On the Effect of Surface Texture and Nanoscale Surface Oxides on the Optical and Mechanical Properties of Silicon Single Crystals and MEMS Thin films

ABSTRACT

This dissertation presents the combined results of analytical, computational and experimental study of the effects of surface texture and nanoscale surface oxides on the optical and mechanical properties of silicon single crystals and MEMS thin films. The first part of this work is focused on the analytical modeling of the reflectance of flat and textured silicon substrates. The model was used to study the reflection behavior of textured silicon surfaces under non-normal incidence. By characterizing the incident light and facets of the silicon wafer with vector geometry, dot products and Phong’s reflection model were used to determine the reflection angles between incident light rays and pyramidal facets. The possible optical interactions are considered for a wide range of pyramidal geometries and light incidence angles that are relevant to the exposure of textured silicon surfaces to incident sunlight. Furthermore, the model was used to investigate the possibility of secondary reflection, for the full range of incidence angles to the substrate. The textured silicon surfaces were found to reduce the reflection angles more effectively than flat substrates at lower angles of incidence. Secondary reflection was also found to be experienced or guaranteed, for all pyramid heights, when the angle of incidence to the substrate was less than 19.4°. The predictions are validated with experimental measurements of reflectance from (001)-textured silicon surfaces. Secondly, the results of an experimental study of the effects of surface texture on the optical and light trapping properties of silicon wafers are presented. Surface texture is controlled by anisotropy etching with potassium hydroxide (KOH) and isopropyl alcohol (IPA) solutions. The effects of KOH/IPA etching on the uniform distribution of pyramidal textures on the (001)-oriented silicon wafer are elucidated. The effects of etchant concentration and KOH/IPA ratio are also explored, along with the effects of etching duration and temperature.