The energy band diagram of n-St in aqueous 2M KOH is constructed by the measured open-circuit potential and the flatband voltage. A photocurrent suseeptivity method was proposed to determine the flatband voltage. A flatband voltage of -1.04 V/SCE (saturated calomel electrode) for the n-St in 2M KOH was determined by this new method. The energy band diagram of the p-St in the same electrolyte is also constructed. Accumulation of carriers at the n-Si/KOH interface is predicted by the band diagram and confirmed by the ohmic-contact-like I-V curve. Depletion of carriers at p-Si/KOH interface is predicted by the band diagram and confirmed by the rectifying I-V characteristics. The passivation of Si under anodic bias is attributed to the formation of an oxide film. The competition between the oxidation rate and the diffusion rate of oxidation product determines whether the anodic oxidation is an etching or passivation process. The etching oxidation is assumed to be dominated by the electrochemical reaction. The transport of these carriers which participate in the electrochemical reaction can be explained by the energy band diagram. All etching or passivation phenomena are consistent with the prediction from the band diagram viewpoint. The etch stop for heavily doped Si is attributed to the enhanced growth rate of oxide film under high carrier concentration.The energy band diagram of the semiconductor electrode is a useful tool for understanding transport phenomena of the carriers in the electrochemical reaction, such as eleetrodeposition or electroless deposition of metal onto semiconductor; selective etching and decomposition of the semiconductor electrode. I-~ To construct the energy band diagram of Si in aqueous KOH, which is involved in the anisotropic etching reaction, is useful in understanding the carrier-transport phenomena as well as the etching mechanism.The anisotropic etching of Si in the alkaline electrolyte has long been recognized and employed in the fabrication of microstructures such as diaphragms, 6-8 cantilever beams, ~ grooves, I~ etc. These mierostructures are important in the manufacture of mierosensors and microactuators which can be integrated in a single chip. The widespread application of the anisotropie etching techniques ca]is for the construction of the quantitative energy band diagram of Si in the alkaline electrolyte to describe the transport of carriers during etching. Palik et al., 11.~2 and Ozdemir and Smith ~3 qualitatively explained the I-V behaviors of Si in KOH by using a simple qualitative energy band diagram. Seidel et al. 14 constructed the energy band diagram of Si in the alkaline electrolyte by aligning the Fermi level between the Si and the electrolyte. They attributed the Fermi level of electrolyte (HzO/OH-) to be 0.8 V/NHE (normal hydrogen electrode) which is the standard redox potential modified by the Nernst equation. Sundaram and Chang also constructed the energy band diagram of Si in hydrazine to give a qualitative explanation of the different I-V behaviors for n-and p-...

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