Properties of light-emitting porous silicon formed by stain etching in HF/KIO3 solution under light illumination

The structural and optical properties of stain-etched porous silicon are investigated using optical microscopy, scanning electron microscopy, ex situ atomic force microscopy (AFM), photoluminescence (PL), and Fourier transform infrared (FTIR) spectroscopy. The stained layers were formed in a 50% HF solution with the addition of an oxidizing agent of KIO(3) on n-type silicon substrates with and without light illumination of lambda=532 nm. Strong yellowish emission is observed only when porous silicon is formed under light illumination and in the limited KIO(3) concentrations. Surprisingly enough, no PL emission is observed on stained surfaces formed without light illumination. The surface morphology as characterized by AFM reveals that light illumination can produce microscopic roughnesses on the stained surfaces. No specific chemical species on the stained surfaces can be identified by FTIR spectroscopy. The origin of the yellowish luminescence is hypothesized to be due to the quantum-size effect that enables the nondirect optical transitions via a momentum conservation relaxation. (C) 2008 American Institute of Physics.