Photodegradation activity and stability of porous silicon wafers with (1 0 0) and (1 1 1) oriented crystal planes

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Hydrogen-terminated porous Si wafers with (100) and (111) oriented crystal planes were fabricated through a photo-electrochemical etching. It is found that the porosity of silicon wafers and their etch rates are determined as a function of crystal orientation. Due to the anisotropic etching behavior of single-crystal silicon, the hydrogen-terminated porous Si (100) wafers exhibit not only more excellent photodegradation activity but also stronger stability for methyl orange degradation than hydrogen-terminated porous Si (111) wafers under visible light irradiation. For the unetched Si wafers, however, the photodegradation activities of methyl orange exhibit a contrary conclusion.