Correlation between the H+ Concentration in the Electrolyte and the Photoluminescence of Porous Silicon

Abstract

We have investigated the photoluminescence (PL) properties of porous silicon (PS) samples prepared in a 20% HF±ethanol electrolyte with different H concentration by varying the added HCl or NH 3 Á H 2 O concentration in the range of 0±6 mol/l at a constant anodic current density. The PL spectra continuously blueshift with increasing NH 3 Á H 2 O concentration or decreasing HCl concentration in electrolyte. Meanwhile, the infrared absorption associated with Si±O gradually increases with the NH 3 Á H 2 O concentration. Raman scattering results indicate that the average particle sizes of the PS samples have no obvious evolution with varying H concentration in electrolyte. These experimental results strongly support that light emission of PS originates from luminescent centers.Introduction The observation of strong visible light emission from porous silicon (PS) has attracted much attention because of its potential application in Si-based optoelectronic devices [1]. Numerous models have been proposed to illustrate the luminescence mechanism including quantum confinement model [1], silicon instrinsic surface state model [2], special luminescence materials (for example, siloxene [3], SiH x complexes [4], polysilanes [5] or defects related to oxygen [6] or silanone-based oxyhydrides [7]), quantumconfinement/luminescence-center model [8,9]. Although the origin of the PL is still controversial, it is usually accepted that surface structure and composition of nanoscale silicon can play a larger role in influencing the photoluminescence (PL) properties of PS. Indeed, a variety of post-treatment methods, including thermal oxidation, chemical oxidation, surface modification, etc. have been performed in an attempt to stabilize or modify the PL properties of PS [10,11]. However, previous experimental studies of the influence on the PL properties of PS by the H concentration of electrolyte are scarce.In this paper, the correlation of the H concentration in electrolyte and the PL properties has been investigated by varying the added HCl and NH 3 Á H 2 O concentration at a constant anodic current density and a constant HF concentration. A continuous blueshift of the PL from PS with decreasing the H concentration has been observed. Furthermore, the origin of the PL is discussed.