The effect of etching time on physical properties of porous silicon fabricated via photo-electrochemical etching technique

porous silicon (PSi) has received a great deal of attention due to the high specific surface area and easy fabrication using some established processes of the usual silicon technology. Porous silicon has been demonstrated being a sensitive sensing platform because of its large internal surface area. The optical and electrical properties of PSi such as refractive index ، photoluminescence and impedance are very sensitive to the presence of biological or chemical species inside the pores. Recently, PSi sensor for detection of different targets such as gases, DNA, and proteins have been reported. An essential requirement for PSi sensor is that the pore s diameter should be large enough to allow easy infiltration of the biological targets but small enough to preserve the large internal surface area to volume ratio that increases the sensitivity. In the present work, we report the behavior of anodized silicon under various etching time parameter and achieving optimum etching time for these processes. All experiments were conducted on square samples (10 mm×10 mm) cut from a single crystalline n-type [100] silicon wafer with a surface resistivity of 0.1-10 Ω/. For cleaning procedure, the silicon substrates were dipped in H2SO4:H2O2 3:1 %wt for 10 minutes and then HF: H2O in 1:9 for 4 minutes, Afterwards, the samples were washed with deionized water and dried under an ambient nitrogen flow. The PS layers were created by etching crystalline silicon (c-Si) in a HF-based photo-electrochemical bath at room temperature under the illumination of a 100W tungsten lamp placed 20 cm above the samples. The electrochemical cell was a Teflon container 10 mm in diameter and 25 mm in height. The solution contained a mixture of hydrofluoric acid (49%), ethanol (95%) and with the volume ratio of 1:4. The silicon substrate was used as an anode electrode, and the cathode was an inert metal (Pt) wire. The etching current density was fixed at 40 mA/cm2 for different etching time of 10, 15, 20, 25, 30 and 35 minutes. It was found that etching time is an important parameter for photo- 13th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 22- 23 Nov, 2017 305 electrochemical etching of n-type silicon. Therefore, by optimizing etching time, the physical properties of PSi samples can be optimized for different applications [1-3].