Environmental Engineering Reference
In-Depth Information
electricalconductors,semiconductors,andinsulators.Thefollowing
sections examine different basic interfaces used in electronic device
structures.Severalofthesebasicinterfacescanthenbecombinedto
form an e
cient PV solar cell.
1.4.1
p-n Junctions
The most basic interface is the p-n junction formed within one
semiconductor crystal lattice having p-type and n-type electrical
conduction in two adjacent regions. These types of junctions are
generally known as homo-junctions, and the energy band diagram
isshowninFig.1.2.Theslopeproducedintheenergybanddiagram
representsthebuilt-inelectricfield(
E
d
V
/d
X
)availablewithin
the device. The region here with this band bending (or the area
with the built-in electric field) is known as the 'depletion region',
and this region is the heart of this basic electronic device. The basic
properties of p-type and n-type semiconductors are summarised in
Table 1.4 for quick reference, but readers are advised to refer to a
suitable textbook for further information on fundamental materials
and device properties [10-12].
When photons with energy (
hf
) greater than the bandgap of
the semiconductor (
hf
≥
E
g
) fall in the depletion region, photons
are absorbed and bonds between the atoms are broken to create
free e-h pairs. The existing internal electric field separates these
photo-generated charge carriers due to their opposite charges,
=−
Figure 1.2
The energy band diagram of a p-n homo-junction and the
mechanism of PV activity within a solar cell based on a p-njunction.
