Chemistry Reference
In-Depth Information
Formation of PS of front-illuminated
n-
Si depends on the wavelength of the light;
formation of large and deep pores does not occur with a white light at wavelength
<800nm, but formation of cylindrical pores occurs at wavelength >867nm.
763
Unfil-
tered lamp radiation results in large pores covered with micro PS and its depth and
shape depend on wavelength distribution. This phenomenon is due to the wavelength-
dependent absorption depth; carriers that are generated deep in the bulk promote pore
growth at the tips of macropores whereas near-surface generation results in the forma-
tion and dissolution of micro PS and lateral growth of the macropores.
The occurrence of the two-layer PS under front illumination depends on light
intensity and the amount of charge passed as illustrated in Fig. 8.43.
16
There is a cor-
relation between the occurrence of two-layer PS and the saturation photocurrent value.
10
Only a single micro PS layer forms at photocurrent densities below the photosatura-
tion value whereas a two-layer PS forms at current densities above the saturation current
as shown in Fig. 8.44. Also, a macro PS layer forms only after a certain amount of
