Fabrication of one-dimensional photonic crystals by photoelectrochemical etching of silicon

The conditions of formation of deep periodic trenches by photoelectrochemical etching of n-Si (100) with linear seeds on the surface are analyzed. Criteria for the proper choice of the period of seed grooves and the etching current density in relation to the doping level of the substrate are formulated. Corrugation of walls is a characteristic feature of the obtained structures; this corrugation is caused by traces of merged macropores. Atomic-force microscopy is used to study roughness of the side-walls in relation to the etching conditions; the current density at which one can obtain the smoothest side-walls is determined. The roughness of the side walls in structures with periods of 7 and 9 μm on Si with the resistivity of 15 Ω cm amounts to ∼40 nm. It is shown that additional treatment of the structures in alkaline solutions can decrease the side-wall roughness by approximately a factor of 2.