Scanning electron microscopy has shown etching of a porous silicon layer in an HF solution to be irregular. The intensity of porous silicon photoluminescence significantly decreases during gradual etching off, and its peak initially shifts to shorter and then to longer wavelengths. Under red-light pulse excitation, photovoltage measurements have shown that the boundary potential φ_s of the p-Si substrate is positive, and φ_s grows with the etching time and as the temperature decreases from 300 to 200 K. At T < 230 K, the photomemory of φ_s caused by nonequilibrium electron capture by p-Si boundary traps is observed. The concentration of shallow traps and boundary electron states in p-Si increases as porous silicon is etched. At T < 180 K, the system of boundary electron states is rearranged. Photovoltage measurements with white-light pulses have revealed electron capture at oxide traps of aged porous silicon.
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