If germanium is doped with gallium three valence electrons , all three electrons are used in bonding, leaving one hole for conduction. This results in a p -type material. The Hall effect is the production of a potential difference due to motion of a conductor through an external magnetic field. This effect can be used to determine the drift velocity of the charge carriers electrons or hole. If the current density is measured, this effect can also determine the number of charge carriers per unit volume.
For an n -type semiconductor, how do impurity atoms alter the energy structure of the solid? For a p -type semiconductor, how do impurity atoms alter the energy structure of the solid? It produces new unfilled energy levels just above the filled valence band. These levels accept electrons from the valence band. An experiment is performed to demonstrate the Hall effect.
A thin rectangular strip of semiconductor with width 10 cm and length 30 cm is attached to a battery and immersed in a 1. This produced a Hall voltage of 12 V. What is the drift velocity of the charge carriers? Suppose that the cross-sectional area of the strip the area of the face perpendicular to the electric current presented to the in the preceding problem is and the current is independently measured to be 2 mA.
What is the number density of the charge carriers? A current-carrying copper wire with cross-section has a drift velocity of 0. Find the total current running through the wire. The Hall effect is demonstrated in the laboratory. A thin rectangular strip of semiconductor with width 5 cm and cross-sectional area is attached to a battery and immersed in a field perpendicular to its surface.
The Hall voltage reads What is the magnetic field? Skip to content Condensed Matter Physics. Learning Objectives By the end of this section, you will be able to: Describe changes to the energy structure of a semiconductor due to doping Distinguish between an n-type and p-type semiconductor Describe the Hall effect and explain its significance Calculate the charge, drift velocity, and charge carrier number density of a semiconductor using information from a Hall effect experiment.
The motion of holes in a crystal lattice. As electrons shift to the right, an electron hole moves to the left. The introduction to impurities and acceptors into a semiconductor significantly changes the electronic properties of this material. The Hall effect. An electric field is generated to the right. An electric field is generated to the left. What kind of semiconductor is produced if silicon is doped with a phosphorus, and b indium?
What is the Hall effect and what is it used for? Problems An experiment is performed to demonstrate the Hall effect. Glossary acceptor impurity atom substituted for another in a semiconductor that results in a free electron donor impurity atom substituted for another in a semiconductor that results in a free electron hole doping alteration of a semiconductor by the substitution of one type of atom with another drift velocity average velocity of a randomly moving particle hole unoccupied states in an energy band impurity atom acceptor or donor impurity atom impurity band new energy band create by semiconductor doping majority carrier free electrons or holes contributed by impurity atoms minority carrier free electrons or holes produced by thermal excitations across the energy gap n -type semiconductor doped semiconductor that conducts electrons p -type semiconductor doped semiconductor that conducts holes.
This type of impurity has 5 valence electrons and is called a pentavalent impurity. Arsenic, antimony, bismuth, and phosphorous are pentavalent impurities.
Because these materials give or donate one electron to the doped material, they are also-called donor impurities. When a pentavalent donor impurity, like arsenic, is added to germanium, it will form covalent bonds with the germanium atoms.
Figure 1 illustrates this by showing an arsenic atom As in a germanium Ge lattice structure. Notice the arsenic atom in the center of the lattice. It has 5 valence electrons in its outer shell but uses only 4 of them to form covalent bonds with the germanium atoms, leaving 1 electron relatively free in the crystal structure. Since this type of semiconductor n-type has a surplus of electrons, the electrons are considered majority carriers, while the holes, being few in number, are the minority carriers.
Conduction in the n-type semiconductor, or crystal, is similar to conduction in a copper wire. That is, with voltage applied across the material, electrons will move through the crystal just as current would flow in a copper wire. The positive potential of a battery will attract the free electrons in the crystal. These electrons will leave the crystal and flow into the positive terminal of the battery. As an electron leaves the crystal, an electron from the negative terminal of the battery will enter the crystal, thus completing the current path.
Therefore, the majority current carriers in the n-type material electrons are repelled by the negative side of the battery and move through the crystal toward the positive side of the battery. The second type of impurity, when added to a semiconductor material, tends to compensate for its deficiency of 1 valence electron by acquiring an electron from its neighbor.
Impurities of this type have only 3 valence electrons and are called trivalent impurities. In an n-type semiconductor, pentavalent impurity from the V group is added to the pure semiconductor. The pentavalent impurities provide extra electrons and are termed as donor atoms.
Electrons are the majority charge carriers in n-type semiconductors. Germanium has four valence electrons. If germanium is doped with gallium three valence electrons , all three electrons are used in bonding, leaving one hole for conduction. This results in a p-type material.
Semiconductors like germanium or silicon doped with any of the trivalent atoms like boron, indium or gallium are called p-type semiconductors. The impurity atom is surrounded by four silicon atoms. It provides the atoms to fill only three covalent bonds as it has only three valence electrons. We know that semiconductors are of two types namely extrinsic and intrinsic. Intrinsic semiconductors are pure semiconductors i.
Aluminium is a p-type dopant, which means that when a semiconductor i. Electrical conductivity of semiconductors increases and resistivity remains the same. Germanium is not an essential element. Its acute toxicity is low. However, at least 31 reported human cases linked prolonged intake of germanium products with renal failure and even death.
Signs of kidney dysfunction, kidney tubular degeneration, and germanium accumulation were observed. Germanium atoms have one more shell than silicon atoms, but what makes for the interesting semiconductor properties is the fact that both have four electrons in the valence shell. As a consequence, both materials readily constitute themselves as crystal lattices.
The process of adding these atoms is known as doping. Germanium oxide has a high index of refraction, meaning light travels through it more slowly. This gives it applications in wide angle lenses for cameras and microscope lenses. In an n-type semiconductor, the donor energy level is close to the conduction band and away from the valence band. In the p-type semiconductor, the acceptor energy level is close to the valence band and away from the conduction band.
In a N-type semiconductor, the majority of charge carriers are free electrons whereas the holes are in minority.
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