Chemistry Reference
In-Depth Information
charge determined by the anodization conditions, which is the etch layer required for
the initiation of macropores as discussed in the previous section.
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There is also an etched layer of Si on the surface of the anodized Si sample under
illumination as illustrated in Fig. 8.45. This etched layer, which unlike that in the dark
is required for the surface roughening for the initiation of pores, is mainly due to pho-
tocorrosion. As a result of the photoinduced dissolution the top surface of the PS layer
recedes with time. The rate of dissolution depends on doping, HF concentration, current
density, and illumination intensity. Figure 8.46 shows the variation of the three layers
with the amount of charges passed; the etched layer on a highly doped sample is thicker
than that on a lowly doped material. The thickness of the micro PS decreases while
pore diameter and etched layer increase with increasing light intensity. Table 8.5 shows
