Functionalized Nano-porous Silicon Surfaces for Energy …
383
a
b
c
30 nm
30 nm
(a)
(b)
30 nm
(c)
Fig. 3 FESEM image, visual images and PL spectra (L is Si crystallize size between two pores)
of samples prepared in different concentration of etching solution for HF:Ethanol a 3:7 b 4:6 c 6:4
at neighboring pores. The walls are not depleted of carriers if the wall thickness is
larger than twice the space-charge layer thickness and dissolution can still occur to
form new pores on the walls. With controlled space-charge layer thickness to form
PS, the actual wall thickness is determined by the relative dissolution rates between
the pore tip (i t ) and the edge of a pore bottom (i b ). If i t is comparable to i b , significant
dissolution occurs at the edge of the pore bottom before the pore tip propagates far
away resulting in a thin wall or the annihilation of walls. On the other hand, The
relatively thick walls and small pore can be generated, if i b is very small compared
to i t , the pore tip propagates relatively fast before much dissolution occurred on
the edge of the pore bottom, where dissolution is virtually stopped due to lack of
carriers. In p-Si by increasing the HF concentration the thickness of the space-charge
383
a
b
c
30 nm
30 nm
(a)
(b)
30 nm
(c)
Fig. 3 FESEM image, visual images and PL spectra (L is Si crystallize size between two pores)
of samples prepared in different concentration of etching solution for HF:Ethanol a 3:7 b 4:6 c 6:4
at neighboring pores. The walls are not depleted of carriers if the wall thickness is
larger than twice the space-charge layer thickness and dissolution can still occur to
form new pores on the walls. With controlled space-charge layer thickness to form
PS, the actual wall thickness is determined by the relative dissolution rates between
the pore tip (i t ) and the edge of a pore bottom (i b ). If i t is comparable to i b , significant
dissolution occurs at the edge of the pore bottom before the pore tip propagates far
away resulting in a thin wall or the annihilation of walls. On the other hand, The
relatively thick walls and small pore can be generated, if i b is very small compared
to i t , the pore tip propagates relatively fast before much dissolution occurred on
the edge of the pore bottom, where dissolution is virtually stopped due to lack of
carriers. In p-Si by increasing the HF concentration the thickness of the space-charge