How Do Extrinsic Semi Conductors Work?
An intrinsic semiconductor is a naturally occurring, pure element. An extrinsic semiconductor is a type of semiconductor which has been doped; when a semiconductor is doped it has a doping agent added which causes the semiconductor to have different electrical properties. Doping is simply adding an impurity to an intrinsic semiconductor. Once the impurity has been introduced, the hole and electron carrier concentration changes. These are then classified as either an N or P type semiconductor based on their electrical properties.
What is doping?
Doping is a process that is used to turn a pure, intrinsic semiconductor into an extrinsic semiconductor. During the doping process, atoms that are impure are introduced into a pure intrinsic semiconductor. Impurity atoms can act as either donors or acceptors when placed into an intrinsic semiconductor. This process changes the hole and electron concentrations in a semiconductor. A donor atom has more valence electrons than the atoms that they are used to replace in the lattice structure of an intrinsic semiconductor. A donor impurity “donates” its extra electrons from its valence to the semiconductor’s conduction band. This action causes the intrinsic semiconductor to have an extra amount of electrons. Having an extra number of electrons changes the electron carrier concentration and transforms it into an N-type semiconductor. An acceptor impurity atom has less valence electrons than the atoms that they will replace in the lattice structure of the intrinsic semiconductor. The acceptor “accepts” electrons from the valence band. But this process provides extra holes in the intrinsic semiconductor. These extra holes increase the hole carriers and it is transformed into a P-type semiconductor. Dopant atoms and semiconductors are both defined based on their position in the periodic table. The column in the periodic table is used to identify how many electrons an atom has in its valence and whether the dopant atoms are acting as a donor or an acceptor.
N-Type Extrinsic Semiconductors
When an extrinsic semiconductor has a larger concentration of electrons than holes, it is called an N-type semiconductor. It is labeled as an “N” type since it has a negative charge. In an N-type semiconductor, the electrons become the majority carriers while the holes remain the minority carriers. To create an N-type semiconductor an intrinsic semiconductor is doped with donor impurities. Phosphorus is one of the most common doping elements used. In an N-type semiconductor the Fermi energy level is greater than an intrinsic semiconductor and it is situated nearer to the conduction band than the valence band.
P-Type Extrinsic Semiconductors
In one way, the P-type semiconductor is the opposite of an N-type since it has a larger hole concentration than electrons. P-type is referring to the hole’s positive charge. In a P-type semiconductor, the hole becomes the majority carrier while the electrons remain the minority carriers. A very common dopant used to form common P-type semiconductors is Boron. In a P-type semiconductor, the Fermi energy level is below intrinsic Fermi energy levels. This means that it lies closer to the valance band than to the conduction band.
What are extrinsic semiconductors used for?
Many commonly used electrical devices have extrinsic semiconductors as one of the components. There are many devices that only allow the current to travel in a single direction and these use a diode. A diode uses both a p-type and an n-type semiconductor and these are placed in conjunction with each other. In most instances, diodes are doped germanium or silicon. Transistors also use extrinsic semiconductors since these are devices which allow switches and switching. One type of transistor is the bipolar junction transistor. The two most common bipolar junction transistors are a NPN type and a PNP type. NPN transistors have two layers of N-type semiconductors with a P-type sandwiched in between them. The PNP transistor has two layers of P-type semiconductors with an N-type sandwiched between. Another kind of transistor that uses an extrinsic semiconductor is the Field-effect transistor. These are unipolar and are not considered to be either an N-channel or P-channel. These types of transistors have two classifications: insulated gate or junction gate. There are numerous devices that use extrinsic semiconductors some examples include:
What is doping?
Doping is a process that is used to turn a pure, intrinsic semiconductor into an extrinsic semiconductor. During the doping process, atoms that are impure are introduced into a pure intrinsic semiconductor. Impurity atoms can act as either donors or acceptors when placed into an intrinsic semiconductor. This process changes the hole and electron concentrations in a semiconductor. A donor atom has more valence electrons than the atoms that they are used to replace in the lattice structure of an intrinsic semiconductor. A donor impurity “donates” its extra electrons from its valence to the semiconductor’s conduction band. This action causes the intrinsic semiconductor to have an extra amount of electrons. Having an extra number of electrons changes the electron carrier concentration and transforms it into an N-type semiconductor. An acceptor impurity atom has less valence electrons than the atoms that they will replace in the lattice structure of the intrinsic semiconductor. The acceptor “accepts” electrons from the valence band. But this process provides extra holes in the intrinsic semiconductor. These extra holes increase the hole carriers and it is transformed into a P-type semiconductor. Dopant atoms and semiconductors are both defined based on their position in the periodic table. The column in the periodic table is used to identify how many electrons an atom has in its valence and whether the dopant atoms are acting as a donor or an acceptor.
N-Type Extrinsic Semiconductors
When an extrinsic semiconductor has a larger concentration of electrons than holes, it is called an N-type semiconductor. It is labeled as an “N” type since it has a negative charge. In an N-type semiconductor, the electrons become the majority carriers while the holes remain the minority carriers. To create an N-type semiconductor an intrinsic semiconductor is doped with donor impurities. Phosphorus is one of the most common doping elements used. In an N-type semiconductor the Fermi energy level is greater than an intrinsic semiconductor and it is situated nearer to the conduction band than the valence band.
P-Type Extrinsic Semiconductors
In one way, the P-type semiconductor is the opposite of an N-type since it has a larger hole concentration than electrons. P-type is referring to the hole’s positive charge. In a P-type semiconductor, the hole becomes the majority carrier while the electrons remain the minority carriers. A very common dopant used to form common P-type semiconductors is Boron. In a P-type semiconductor, the Fermi energy level is below intrinsic Fermi energy levels. This means that it lies closer to the valance band than to the conduction band.
What are extrinsic semiconductors used for?
Many commonly used electrical devices have extrinsic semiconductors as one of the components. There are many devices that only allow the current to travel in a single direction and these use a diode. A diode uses both a p-type and an n-type semiconductor and these are placed in conjunction with each other. In most instances, diodes are doped germanium or silicon. Transistors also use extrinsic semiconductors since these are devices which allow switches and switching. One type of transistor is the bipolar junction transistor. The two most common bipolar junction transistors are a NPN type and a PNP type. NPN transistors have two layers of N-type semiconductors with a P-type sandwiched in between them. The PNP transistor has two layers of P-type semiconductors with an N-type sandwiched between. Another kind of transistor that uses an extrinsic semiconductor is the Field-effect transistor. These are unipolar and are not considered to be either an N-channel or P-channel. These types of transistors have two classifications: insulated gate or junction gate. There are numerous devices that use extrinsic semiconductors some examples include: