Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

Cláudia R B Miranda,Antonio F Beloto,Maurício R Baldan,Neidenêi G Ferreira

doi:10.1590/s0103-50532008000400022

Abstract

Porous silicon (PS) samples were obtained by anodization etching process of n-type silicon wafer phosphorus-doped. Electrochemical oxidation of PS was investigated in aqueous hydrofluoric acid (HF) containing additive such as ethanol or acetonitrile. Pore formation was studied with the variation of type and resistivity of the silicon wafer, taking into account the most important anodization process parameters such as: acid concentration, current density and anodization time. Scanning Electron Microscopy (SEM) and Raman Scattering Spectroscopy measurements were used to characterize the macropore morphology changes and sample photoluminescense responses, respectively. PS layer formed in HF-acetonitrile solution showed more uniform and homogeneous macropore distributions with different shapes and sizes. Behavior may be explained because acetonitrile surface tension is greater than that of ethanol. Therefore, acetonitrile molecules might passivate the silicon surface dissolved during the anodization process.

Highlights

Since the discovery of its visible photoluminescence (PL) at room temperature, porous silicon (PS) has been intensively studied
It is important to remember that the silicon is under anodic bias, which depends on the composition and pH of the electrolyte, and PS formation is only observed as long as the current density is below of the critical current density, JPS
Removing the Si atom an atomic size dip remains enhancing the surface inhomogeneity because of the changes in the electric field distribution. This argument was supported in the literature, from the chemical composition studies of PS layer, using IR spectroscopy measurements showing that the silicon surface is terminated with hydrogen, the Si-F (6 eV) bond is much strong than Si-H bond.[7,12,14,18,19,20,21,22,23,24]

Summary

Introduction

Since the discovery of its visible photoluminescence (PL) at room temperature, porous silicon (PS) has been intensively studied. Porous Si might be formed by electrochemical etching of single monocrystalline Si in HF solutions containing additives as ethanol or acetonitrile (MeCN). The anodization process was firstly studied by Bomchil. PS layers were studied intensively, there are still questions about the dissolution chemistry of Si, and different mechanisms have been proposed.[7,8] In general, it is discussed and accepted in the literature that holes (h+) are required for both electropolishing and pores formation, where two hydrogen atoms are evolved for Morphological and Optical Characteristics of Porous Silicon Produced by Anodization Process

Objectives

Results

Conclusion