Application of UV-VIS and FTIR Spectroscopic Ellipsometry to the Characterization of Wet-Chemically Treated Si Surfaces

Abstract

In this paper, investigations of roughness, oxide and hydrogen coverage of Si(111) surfaces after various wet‐chemical treatments using spectroscopic ellipsometry (SE) both in the ultraviolet/visible (UV‐VIS) and in the infrared (IR) spectroscopic region are reported. FTIR SE measurements yielded detailed information on the Si–H bonds on the surface of H‐terminated Si(111) wafers. The characteristic structure in the IR ellipsometric spectra at 2083 cm—1 can be modeled by an anisotropic oscillator. A correlation is established between the morphological structure of the cleaned Si surface caused by chemical preparation and the resulting electronic surface properties monitored by additional surface photovoltage (SPV) measurements. The results of these systematic investigations have been successfully used for optimization of wet‐chemical preparation methods aimed at atomically flat H‐terminated Si(111) surfaces with very low surface state densities. Additionally, native oxide growth on initially H‐terminated Si(111) was correlated to the evolution of rechargeable interface states determined by SPV measurements.

Wet-Chemical Preparation of Textured Silicon Solar Cell Substrates: Surface Conditioning and Electronic Interface Properties

“…For this purpose nominally intrinsic (i)a-Si:H films, (~10 nm) were deposited in a 13.56 MHz parallel plate PECVD system described elsewhere [3]. The relations between structural imperfections at Si surfaces, light trapping behavior, energetic distribution of interface state D it (E) and charge carrier life times (τ eff ) were investigated by scanning electron microscopy (SEM), surface photovoltage (SPV) [4], microwave detected photo conductance decay (µW-PCD) [5], quasi-steady-state photo conductance (QSSPC) [6], and UV-NIR-reflectance measurements [7,8].…”

“…closer to the valence band edge. These states, typically observed on microscopically rough surfaces, are related to strained bond defects and defects on Si atoms of lower stage of oxidation, Si +1 (Si 2 O≡Si−) e.g formed by hydroxyl groups [7] .…”

“…The D it in the upper half of the gap, i.e. closer to the conductivity band edge, results from dangling bonds of the next higher stage of oxidation Si +2 (SiO 2 ≡Si−) and were found to be strongly related to the stage of Si surface oxidation [7]. In order to elucidate the influence of wet-chemical oxide removal, as shown in Fig.…”

Field Manipulation of Band Properties in Infrared Spectra of Thin Films

“…[81,83] This assignment was already discovered decades ago in ref. [84]. Somehow, this interesting property of H-passivated Si(111) surfaces has fallen into oblivion.…”