Pore orientation and shape

The growth of individual pores, or the dissolution at pore tips, is anisotropic and thus depends on the orientation of the substrate. It is also determined by direction of the carrier source pores tend to grow toward the carrier source. The relative effect of substrate orientation and direction of the carrier source on the orientation of pores is determined by the specific electrochemical reactions at the silicon/electrolyte interface at the pore bottoms under a given set of formation conditions. 

The orientation of primary pores is in general in the 100 direction for all of the PS formed on (100) substrate. ° For PS with the dendritic structure shown in Fig. 8.32, pores propagate along the (100) direction even on(110)and(lll)substrates.  

FIGURE 8.32. Dendritic PS morphology formed on n(lOO), 12Gcm in 4% HF at 4mA/cm After JSger 

FIGURE 8.33. Schematic illustration of the growth direction of dendritic PS in relation to the crystal orientation of the silicon sample. After Lehmann and Foll. (Reproduced by permission of The Electrochemical Society, Inc.) 

The dependence on substrate orientation for the macropores formed on p-Si is similar to that on The macropores formed on p-Si in anhydrous HF organic 

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