8.1
8.1.1
8
Semiconductor junctions
Almost all solar cells contain junctions between (different) materials of different doping.
Since these junctions are crucial to the operation of the solar cell, we will discuss their
physics in this chapter.
A p-n junction fabricated in the same semiconductor material, such as c-Si, is an
example of a p-n homojunction. There are also other types of junctions: A p-n junction
that is formed by two chemically different semiconductors is called a p-n heterojunction.
In a p-i-n junction the region of the internal electric field is extended by inserting an
intrinsic, i, layer between the p-type and the n-type layers. The i-layer behaves like a
capacitor: it stretches the electric field formed by the p-n junction across itself. Another
type of the junction is between a metal and a semiconductor; this is called a MS junction.
The Schottky barrier formed at the metal-semiconductor interface is a typical example of
the MS junction.
p-n homojunctions
Formation of a space-charge region in the p-n
junction
Figure 8.1 shows schematically isolated pieces of a p-type and an n-type semiconductor
and their corresponding band diagrams. In both isolated pieces the charge neutrality is
maintained. In the n-type semiconductor the large concentration of negatively-charged
free electrons is compensated by positively-charged ionized donor atoms. In the p-type
semiconductor holes are the majority carriers and the positive charge of holes is
compensated by negatively-charged ionized acceptor atoms. For the isolated n-type
semiconductor we can write
For the isolated p-type semiconductor we have
8.1.1
8
Semiconductor junctions
Almost all solar cells contain junctions between (different) materials of different doping.
Since these junctions are crucial to the operation of the solar cell, we will discuss their
physics in this chapter.
A p-n junction fabricated in the same semiconductor material, such as c-Si, is an
example of a p-n homojunction. There are also other types of junctions: A p-n junction
that is formed by two chemically different semiconductors is called a p-n heterojunction.
In a p-i-n junction the region of the internal electric field is extended by inserting an
intrinsic, i, layer between the p-type and the n-type layers. The i-layer behaves like a
capacitor: it stretches the electric field formed by the p-n junction across itself. Another
type of the junction is between a metal and a semiconductor; this is called a MS junction.
The Schottky barrier formed at the metal-semiconductor interface is a typical example of
the MS junction.
p-n homojunctions
Formation of a space-charge region in the p-n
junction
Figure 8.1 shows schematically isolated pieces of a p-type and an n-type semiconductor
and their corresponding band diagrams. In both isolated pieces the charge neutrality is
maintained. In the n-type semiconductor the large concentration of negatively-charged
free electrons is compensated by positively-charged ionized donor atoms. In the p-type
semiconductor holes are the majority carriers and the positive charge of holes is
compensated by negatively-charged ionized acceptor atoms. For the isolated n-type
semiconductor we can write
For the isolated p-type semiconductor we have