Influence of Hydrogen Peroxide on the Photoanodization of n-Si in the Breakdown Mode
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The electrochemical etching of n-Si (100) in an electrolyte composed of 4% HF solution in 30% hydrogen peroxide is experimentally studied at a voltage exceeding the breakdown voltage. The effect of the illuminance of the wafer back side on the porous-structure morphology and such parameters as porosity, effective valence, and pore growth rate are examined. The data obtained are compared with those for structures subjected to photoanodization in an aqueous electrolyte at the same HF concentration. It is found that the presence of hydrogen peroxide strongly changes the morphology of macropores, makes their diameter smaller, and raises by a factor of ~2 the rate of growth deeper into the substrate. In the presence of H2O2, there appear inclined secondary pores oriented at an angle of 15°–35° to the main channel axis and a number of breakthrough mesopores propagating in the 〈100〉 directions in the plane parallel to the sample surface. The effective valence of the electrochemical dissolution of silicon in the HF:H2O2 electrolyte at a low illumination level is close to unity and grows with increasing light intensity, always being smaller than 2.
We are grateful to D.N. Goryachev, O.M. Sreseli, and V.P. Ulin for reading the manuscript and helpful discussions. The electron-microscopic analysis was made by A.I. Likhachev on equipment of the Federal Collective Use Center “Materials science and diagnostics in advanced technologies,” supported by the Ministry of Education and Science of the Russian Federation (unique project identifier RFMEFI62117X0018).