Investigation of stability of electrophysical parameters of Si-wafers before forming porous layer

Abstract

The article studies the influence of Si-wafers processing in acid-peroxide and ammonia-peroxide solutions on the temporary stability of the electronic states of the crystal surfaces before formation of the nanostructured and porous silicon layers. A characteristic parameter of stability of the electrical properties of a semiconductor was selected the change in contact potential difference over time, which was measured by Kelvin. After alkaline treatments during the storage of Si-wafers in air, their contact potential difference decreases with time. The change in the contact potential difference for this type of treatments is small and most of them (up to120 hours) does not reach steady-state values in the studied interval of time. This fact indicates that Si surface is unstable after the treatment in ammonia-peroxide solutions and is characterized by long relaxation changes of the contact potential difference. In case of acid treatments or their combinations with alkaline ones, the changes of the contact potential difference over time is characterized by a sharp decrease during 20 ÷ 40 hours and subsequent attainment of steady-state values of the contact potential difference. This indicates more efficient processing of Si-wafers in acid-peroxide solutions than in ammonium peroxide ones. It was shown experimentally that the time necessary to reach the steady-state values ​​of the contact potential difference and the time of electron activity after Si-wafers surface treatment in acid-peroxide solutions is less than in ammonia-peroxide solutions. The results are treated by the formation on Si surface of oxide and hydroxyl layers that leads to the formation of macroporous, and microporous or mesoporous silicon layers