On the morphology and the electrochemical formation mechanism of mesoporous silicon

Electrochemical pore formation in silicon electrodes is a well-known phenomenon. While micropore formation is commonly understood as due to quantum size effects, the formation of larger pores is dominated by the electric field of the space charge region. In contrast to the macropore regime which is well understood, little is known about the morphology and formation mechanism of mesopores. In this report mesopore morphology and its dependence on formation parameters, such as HF concentration, current density, bias, and substrate doping density, is investigated in detail. In addition, a simulation of the breakdown conditions at the pore tip is performed which shows that mesopore formation is dominated by charge carrier tunneling, while avalanche breakdown is found to be responsible for the formation of large etchpits.