Environmental Engineering Reference
In-Depth Information
p-region
n-region
Holes
Electrons
Depletion layer
16
10
Holes
Charge carrier
density per cm
3
10
Electrons
10
+
+
+
+
+
+
+
+
Space-charge
density
-
-
-
-
-
-
-
-
-
-
-
Fig. 6.4
Creation of a depletion layer within the p-n-junction (various sources)
Fig. 6.5 shows idealised conditions. Simplified, it has been assumed that major-
ity carrier density is negligible over the entire space-charge region and that deple-
tion layer density (Fig. 6.5 c) remains constant up to the edges of the depletion
zone. This also implies that the respective doping concentration is constant up to
the p-n-border; p-n-transition is thus abrupt. Fig. 6.5 d shows the corresponding
potential curve of a positively charged particle and the diffusion voltage created
within the depletion layer.
p-material
n-material
Stationary charge:
to acceptor atoms
to donator atoms
a
Without irradiation
creation of a depletion layer
Free charge carries:
Holes (p)
Electrons (n)
Depletion
layer
Number of holes
Number of electrons
b Carrier density for holes and
electrons on the p- und the n-side
+
c Space charge (ideal case)
-
U
D
d Diffusion voltage (
U
)
D
e
Irradiation
Energy gap model showing the p-n-junction
(charge carrier pairs generated by light are
separated by diffusion voltage)
E (x)
e U
0 D
C
E (x)
V
E (x)
= Energy level of the valence band
E (x)
= Energy level of the conduction band
C
Generation by
light absorption
V
Diffusion zone
Fig. 6.5
p-n-junction within a solar cell (
e
0
elementary charge) (various sources)
Search WWH ::
Custom Search