Selective etching of silicon in aqueous KOH

The polarization curves of p-type and n-type silicon in aqueous KOH were studied, It is indicated that both p-Si and n-Si exhibit active-passive-transpassive behaviour, The difference in polarization curve between these two types of Si is attributed to the carriersʹ transport limitation, In the p-Si, the electrons are limited, and the cathodic current is consequently restricted. On the contrary, the holes are limited for the n-Si, and hence the anodic current as well as passive film formation are restricted. This carrier transport limitation model for silicon is quite different from the model for the metals that demonstrate a passivity effect. Since the passivation potential and open-circuit potential are different for p-Si and n-Si in aqueous KOH. selective anisotropic etching can be achieved by applying a proper external potential, Both depressed and protruding cross-patterned n-type zones on a p-type substrate have been fabricated by applying a proper potential to the p-n junction.