Chemistry Reference
In-Depth Information
where
and are bulk electron and hole densities, respectively, and
At the surface where
x =
0,
Three types of space charge layers, namely, depletion layer, accumulation layer, and
inversion layer, may occur in a semiconductor depending on the bias and equilibrium
conditions as shown in Fig. 1.7.
1.3.2. Depletion Layer
When the surface region is depleted of majority carriers, due to positive band
bending for
n
type or negative band banding for
p
type, a depletion layer is formed as
shown in Fig. 1.7(a). The depletion layer has no mobile carriers but has immobile
charges associated with the ionized dopants. The Poisson equation, Eq. (1.16) for
n
-type material, can be reduced to
On integration with
dV/dx
(
V
= 0) = 0 one obtains
