On the role of the pore filling medium in photoluminescence from photochemically etched porous silicon

Abstract

Porous silicon thin films created under laser illumination in fluoride solutions without biasing have been studied by a variety of techniques to investigate the film structure and photoluminescence (PL). The use of ultrathin silicon wafers allows us to perform plan view transmission electron microscopy studies without recourse to thinning procedures that might adversely affect the film structure. Supercritically dried samples are compared to air dried samples and clearly demonstrate the deleterious effects of air drying on film structure. PL studies were performed (a) while the sample is submerged in aqueous HF, (b) in Ar after rinsing in ethanol, and (c) in air after rinsing in ethanol. The wavelength of light used to fabricate the film is found to correlate strongly with the peak PL wavelength when measured in solution. Little correlation is found in Ar or in air. Exposure to air can change the PL spectrum dramatically on a time scale of just seconds. We demonstrate that samples can exhibit essentially identical PL spectra in one medium but have spectra that differ from one another when the samples are placed in a different medium. The PL results indicate that band-to-band recombination cannot explain photon emission under all circumstances, and that surface states must also be involved in radiative processes under those conditions in which the bands are sufficiently separated to allow for the appearance of gap states.

Laser-Assisted Formation of Porous Si in Diverse Fluoride Solutions: Reaction Kinetics and Mechanistic Implications

“…33 We have not verified by in situ infrared absorption measurements whether an oxide layer forms during photoelectrochemical etching as employed in this study, corresponding to the electropolishing regime above the critical current density in anodic etching. However, since a por-Si layer forms, which we have confirmed by scanning electron microscopy, 34,35 photoluminescence, 35,36 profilometry, 22 and porosity measurements, 37 the reaction we observe is within the porous silicon formation regime rather than the electropolishing regime. Moreover, we have previously shown 22 that Gaussian laser intensity profiles lead to Gaussian film profiles.…”

Investigation to planar optical waveguides based on oxidised porous silicon/PMMA-DR1 by dark mode spectroscopy method

“…The Bruggeman equation for oxidised porous silicon inserted polymer PMMA-DR1can be written as: The calculated index of film can be obtained according measured porosity ρ of oxidised porous silicon and the polymer fraction γ from Eq. (8). Table 1 shows that the calculated refractive index based on Bruggeman model are conform to measured results generally in our experiment.…”

“…The solution was filtrated to remove foreign substance. The deposition method of immersion under ultrasonic agitation can be used to add the solution into the pore of oxidised porous silicon in our experiment 8 . Three oxidised porous silicon samples with the same porosity were prepared under different ultrasonic agitation time.…”

Luminescence properties of ultrasmall amorphous Si nanoparticles with sizes smaller than 2nm

“…Some experimental data and theoretical investigations suggested that amorphous Si nanostructures are subjected to quantum confinement effect [6][7][8], while others showed that the short mean free path, order of 1 nm, of amorphous Si is responsible for no quantum confinement effect [2,4,9]. In addition, it was found that the quantum confinement mechanism alone cannot be used to explain the influence of various surface treatments and surrounding media on the luminescence properties [10][11][12]. Some theoretical calculations have shown that optical properties of silicon nanoparticles are highly sensitive to localized surface states, which exist in the form of self-trapped excitons and are stabilized in smaller nanoparticles due to the band gap widening [13].…”