Electrochemical Preparation of In-Silicon Hierarchical Networks of Regular Out-Of-Plane Macropores Interconnected by Secondary In-Plane Pores Through Controlled Inhibition of Breakdown Effects

In-silicon hierarchical networks of ordered out-of-plane macropores interconnected by high-density secondary in-plane pores are prepared by controlled electrochemical etching of n-type silicon in HF:H2O2 electrolyte through the synergistic use of back-side illumination, avalanche breakdown anodization voltage, and high-oxidizing-power chemical. Preparation of the hierarchical networks of pores is enabled by controlled inhibition of breakdown effects at high anodization voltages (in the breakdown region) through back-side illumination of the silicon electrode. Inhibition of breakdown effects in pre-patterned silicon electrodes etched under galvanostatic condition at high anodization voltages is used to simultaneously control formation of out-of-plane macropores by regulating the photogenerated etching current density flowing at the pore tips and enable in-plane branching of out-of-plane pores by increasing leakage current at the lateral pore surface through high voltage effects. Further, high-oxidizing-power chemical, namely H2O2, is used to increase density, length, and diameter of branching and, in turn, enable interconnection of out-of-plane macropores with in-plane secondary pores.