Effect of irradiant wavelength during porous silicon formation

Photoelectrochemical etching of silicon using light assistance of various wavelengths has been studied. As the etching process proceeds, a blueshift is noted in the photoluminescence spectra. However, after a certain period of etching, under a fixed current density, a saturation point is reached, below which no further shift to higher energies is detected. This cutoff point occurs at approximately 2 eV, even if a much higher energy irradiant light source is used during the formation process. These results provide strong evidence for the surface-state mechanism of luminescence and render the pure quantum confinement model unlikely.