Fabrication of Radially Symmetric Graded Porous Silicon using a Novel Cell Design

Mingrui Zhao,Manish Keswani

doi:10.1038/srep24864

Abstract

A contactless method using a novel design of the experimental cell for formation of porous silicon with morphological gradient is reported. Fabricated porous silicon layers show a large distribution in porosity, pore size and depth along the radius of the samples. Symmetrical arrangements of morphology gradient were successfully formulated radially on porous films and the formation was attributed to decreasing current density radially inward on the silicon surface exposed to Triton® X-100 containing HF based etchant solution. Increasing the surfactant concentration increases the pore depth gradient but has a reverse effect on the pore size distribution. Interestingly, when dimethyl sulfoxide was used instead of Triton® X-100 in the etchant solution, no such morphological gradients were observed and a homogeneous porous film was formed.

Highlights

The porosification of silicon is conventionally obtained by anodic dissolution of a silicon wafer in a fluoride-based electrolyte solution, as first described by Uhlir in 19581
In the setup demonstrated by Collins et al and Khung et al, a Pt electrode was placed perpendicular to the silicon surface at one end of the sample, causing the potential at silicon-electrolyte interface to be a function of the distance between working and counter electrodes, resulting in a current density gradient on the sample surface from one end to the other[20,21]
We are proposing a new design that is a modification of the geometry we have reported before for fabrication of Porous silicon (PSi) with morphological gradient[23]

Summary

Graded Porous Silicon using a Novel

Cell Design received: 18 December 2015 accepted: 06 April 2016 Published: 22 April 2016. Symmetrical arrangements of morphology gradient were successfully formulated radially on porous films and the formation was attributed to decreasing current density radially inward on the silicon surface exposed to Triton® X-100 containing HF based etchant solution. We are proposing a new design that is a modification of the geometry we have reported before for fabrication of PSi with morphological gradient[23] This innovative and scalable method for PSi formation relies on redox reactions occurring at silicon-solution interfaces. Modifications of the previous experimental setup and use of suitable additives in the HF etchant solution allowed the formation of PSi with a wide distribution of porosity, pore size and pore depth and in a radially symmetrical arrangement, which can be expected to meet the increasing demands for special applications in biosensors, filters and optoelectronic materials. In our process, the only contact of the silicon is with the etchant and deposition solutions (NiSO4/H3BO3), the process is completely scalable

Results

Methods

Additional Information