Porous Silicon Surface Passivation Research Articles

EFFECT OF CHLORINATION ON PHOTOLUMINESCENCE PROPERTIES OF POROUS SILICON

The surface passivation of porous silicon plays a significant role in emission efficiency of the material. Photoluminescence (PL) studies were carried out for p-type porous silicon and chlorinated porous silicon to understand the effect of surface passivation on porous silicon. Visible photoluminescence was observed at 625 nm for both porous silicon and chlorinated porous silicon. The whole sample exhibits a PL band at red region and intensity decreased in chlorinated porous silicon. This paper presents an analytical solution that covers contributions from the components of silicon tetra chloride interface, silicon backbone, and voids using a serial–parallel capacitance method. Simulation study indicates that there is a good correlation between theory and observed PL.

STRUCTURAL AND PHOTOLUMINESCENCE PROPERTIES OF POROUS SILICON: EFFECT OF SURFACE PASSIVATION

The surface passivation of porous silicon is a determining factor in the emission efficiency of the material. The hydrogen surface coverage has been shown to provide very efficient passivation. In this work, we have monitored Si–H n surface coverage, which is readily-obtained porous silicon formed at 1:3 concentrations of HF: ethanol with/without HCl content in the electrolytes, and relate it to the emission efficiency. SEM, FTIR and PL studies were carried out to understand the role of HCl content in the electrolytes. When samples are anodized with HCl content in the electrolytes, there is a net decrease in the concentration of the Si–H groups on the material surface. This treatment provokes desorption of the hydrogen atoms and results in a drastic decrease in the photoluminescence.

Evolution of the porous silicon sample properties in the atmospheric ambient

Evolution of the integral intensity of the photoluminescence (IIPL) of untreated and treated (48% HF etched) porous silicon (PS) samples is studied in samples stored in the air both in the dark and in daylight. It is established that IIPL of the illuminated samples rises with time more rapidly for the etched samples than for the untreated ones. The luminescence efficiency of the unilluminated samples practically does not change. The mechanism of the light effect on sample photoluminescence can be related to an increase of the ambient air ionicity, which is favorable to the reaction of atmospheric oxygen with silicon during the PS surface passivation and the oxide formation. The influence of HF etching duration on sample IIPL is also studied. The effect of HF on the luminescent properties depends on the treatment time and the initial intensity of sample photoluminescence.

Relationship of Processing Parameters to Photoluminescence Intensity and Mechanical Failure in Thick Porous Silicon Layers

The surface passivation of porous silicon has received much attention. While nuclear magnetic resonance may be able to provide insight into the surface passivation of porous silicon, relatively thick (>40 μm) layers are desired. However, mechanically stable layers could only be produced within identifiable ranges of HF concentration, current density, and anodization time. This information allowed sample preparation for nuclear magnetic resonance characterization of porous silicon. In addition, an inverse correlation between mechanical stability and photoluminescence intensity was observed. In a pairwise comparison, similar porosity and surface passivation were maintained as anodization time increased under otherwise constant conditions. However, at the longer anodization time, photoluminescence intensity and surface area increased. To account for these observations, we hypothesize that the thickness of the silicon wall between pores decreases as electrochemical etching proceeds. Decreasing wall thickness could lead to both mechanical failure and increase the probability of creating regions of quantum confinement. A larger number of quantum confined regions, having the same surface passivation, could account for the observed increased photoluminescence intensity.

Fourier transform IR monitoring of porous silicon passivation during post-treatments such as anodic oxidation and contact with organic solvents

The surface passivation of porous silicon is a determining factor in the emission efficiency of the material. The hydrogen surface coverage has been shown to provide very efficient passivation. In this work, we have performed Fourier transform IR (FTIR) measurements to monitor the Si-H surface coverage, which is readily obtained after the layer formation in HF, during different post-treatments (anodic oxidation and contact with organic solvent) and to relate it to the emission efficiency. FTIR studies, performed at different steps of the electrochemical oxidation, indicate that, during the anodic treatment, the hydrogen surface coverage is preserved and that the oxidation takes place on the back bonds of the surface silicon atoms. The importance of the hydrogen coverage is also shown by the analysis of porous layers treated in boiling CCl 4 after formation. This treatment provokes the desorption of the hydrogen atoms and results in a drastic decrease in the photoluminescence. When samples are immersed in boiling methanol after formation, FTIR analyses show that there is also a partial loss of the hydrogen coverage, but accompanied with an oxidation of the material, so that no significant changes in the emission efficiency can be observed.