Nanostructured surfaces

Effect of the conductivity type of Si wafers on morphology of Si nanorods obtained via metal-assisted chemical etching
Nichkalo S.I.1, Druzhinin A.A.1, Chekaylo M.V.2

1 Department of Semiconductor Electronics, Lviv Polytechnic National University, 
S. Bandera Str., 12, Lviv-79013, Ukraine
E-mail: nichkalo@gmail.com
2 Department of Organic Chemistry, Lviv Polytechnic National University, 
S. Bandera Str., 12, Lviv-79013, Ukraine

The metal-assisted chemical etching method (MACE) is becoming increasingly developing, since it involves the use of simple equipment, and the technological process takes place at ambient pressure and room temperature. In general, MACE occurs for any type and doping level of the initial material, because the local oxidation dissolution is activated by holes generated from the outside. Etching occurs exclusively underneath the metal catalyst. However, if the generated holes diffuse in the area above the metal-semiconductor interface, porous nanorods can be formed. Excessive hole generation (high concentration of H2O2) or significant etching-out of Si4+ (high concentration of HF) allow holes to diffuse to areas between patterned metal catalysts. Hence, solid nanorods can only be obtained when a balance is reached between the ratio of the HF and H2O2 concentrations, and beyond this balance from both sides of the concentration chart, porous structures will be formed [1]. 
In this research, we represent the results of studies on fabrication of Si nanorods on the surface of Si wafers of different doping type using the MACE method. The influence of the deposition time of Ag particles on their morphology and filling density on the surface of Si wafers has been analyzed. We show that at different etching time of wafer samples of n-type in a HF-H2O2 based etching solution, vertically aligned arrays of solid nanorods are obtained. It is also shown that by varying the duration of Ag particles deposition at the same etching time, it is possible to change the distance between the nanorods. It was established that under identical technological conditions the nanorods were not formed on a p-Si wafer. The results are discussed from the point of view of the specific etching mechanism of Si wafers with different conductivity type.

1.	Chern W., Hsu K. et al. Nonlithographic patterning and metal-assisted chemical etching for manufacturing of tunable light-emitting silicon nanowire arrays // Nano Lett.-2010.-10.-P. 1582-1588.