Drift current
Encyclopedia
In condensed matter physics
and electrochemistry
, drift current is the electric current
, or movement of charge carrier
s, which is due to the applied electric field
, often stated as the electromotive force
over a given distance.When an electric field is applied across a semiconductor material,the current is produced due to flow of charge carriers.The positively charged particles called holes move with the electric field, whereas the negatively charged electrons move against the electric field. It is distinguished from diffusion current
(manifested via thermal and/or density gradients), which results from the random Brownian motion
of charge carriers independent of electrical stimulus.
If an electric field is applied to an electron existing in a free space, it will accelerate the electron in a straight line from the negative terminal to the positive terminal of the applied voltage.But same thing does not happen in the case of electrons available in good conductors. Good conductors have plenty of free electrons moving randomly in between the fixed positive ion cores. This random movement of electrons in a straight line is known as drift current. Drift current also depends on the mobility of charge carriers in the respective conducting medium.
diode, electrons and holes are the minority charge carriers in the p-region and the n-region, respectively. Due to the diffusion of the majority charge carriers across the junction, an electric field is developed across the junction, called barrier potential. The further diffusion of the majority charge carriers is hindered by this potential barrier. But at the same time, the minority carriers can cross the junction as it is a downhill journey for them. When the minority charge carriers are generated thermally near the junction, they drift slowly along the junction plane, aided by the electric field of the barrier potential. This current, which arises because of the motion of the drift of minority charge carriers, is the drift current in a p-n junction diode. It flows in a direction opposite to the diffusion current
which arises owing to the motion of the majority charge carriers across the junction.
At equilibrium in an unbiased p-n junction diode, the diffusion current, which flows from the p to n region, is exactly balanced by the equal and opposite drift current.
In a biased p-n junction, the drift current is independent of the biasing, as the number of minority carriers is independent of the biasing voltages. But as minority charge carriers can be thermally generated, drift current is temperature dependent.
→ When an electric field is applied across the semiconductor material, the charge carriers attain a certain drift velocity Vd, which is equal to the product of the mobility of the charge carriers and the applied Electric Field intensity E;
Drift velocity Vd = mobility of the charge carriers × Applied Electric field intensity.
→ Holes move towards the negative terminal of the battery and electrons move towards the positive terminal of the battery. This combined effect of movement of the charge carriers constitutes a current known as "drift current" .
→ Drift current due to the charge carriers such as free electrons and holes is the current passing through a square centimeter area perpendicular to the direction of flow.
(i) Drift current density Jn, due to free electrons is given by
Jn = q n μn E (A / cm2)
(ii) Drift current density JP, due to holes is given by
JP = q p μp E (A / cm2)
Where, n - Number of free electrons per cubic centimeter.
P - Number of holes per cubic centimeter
μn – Mobility of electrons in cm2 / Vs
μp – Mobility of holes in cm2 / Vs
E – Applied Electric filed Intensity in V /cm
q – Charge of an electron = 1.6 × 10−19 coulomb.http://www.srmuniv.ac.in/downloads/drift_and_diffusion_currents.doc
Condensed matter physics
Condensed matter physics deals with the physical properties of condensed phases of matter. These properties appear when a number of atoms at the supramolecular and macromolecular scale interact strongly and adhere to each other or are otherwise highly concentrated in a system. The most familiar...
and electrochemistry
Electrochemistry
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...
, drift current is the electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
, or movement of charge carrier
Charge carrier
In physics, a charge carrier is a free particle carrying an electric charge, especially the particles that carry electric currents in electrical conductors. Examples are electrons and ions...
s, which is due to the applied electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
, often stated as the electromotive force
Electromotive force
In physics, electromotive force, emf , or electromotance refers to voltage generated by a battery or by the magnetic force according to Faraday's Law, which states that a time varying magnetic field will induce an electric current.It is important to note that the electromotive "force" is not a...
over a given distance.When an electric field is applied across a semiconductor material,the current is produced due to flow of charge carriers.The positively charged particles called holes move with the electric field, whereas the negatively charged electrons move against the electric field. It is distinguished from diffusion current
Diffusion current
-Introduction:Diffusion current is a current in a semiconductor caused by the diffusion of charge carriers . Diffusion current can be in the same or opposite direction of a drift current, that is formed due to the electric field in the semiconductor...
(manifested via thermal and/or density gradients), which results from the random Brownian motion
Brownian motion
Brownian motion or pedesis is the presumably random drifting of particles suspended in a fluid or the mathematical model used to describe such random movements, which is often called a particle theory.The mathematical model of Brownian motion has several real-world applications...
of charge carriers independent of electrical stimulus.
If an electric field is applied to an electron existing in a free space, it will accelerate the electron in a straight line from the negative terminal to the positive terminal of the applied voltage.But same thing does not happen in the case of electrons available in good conductors. Good conductors have plenty of free electrons moving randomly in between the fixed positive ion cores. This random movement of electrons in a straight line is known as drift current. Drift current also depends on the mobility of charge carriers in the respective conducting medium.
Drift current in a p-n junction diode
In a p-n junctionP-n junction
A p–n junction is formed at the boundary between a P-type and N-type semiconductor created in a single crystal of semiconductor by doping, for example by ion implantation, diffusion of dopants, or by epitaxy .If two separate pieces of material were used, this would...
diode, electrons and holes are the minority charge carriers in the p-region and the n-region, respectively. Due to the diffusion of the majority charge carriers across the junction, an electric field is developed across the junction, called barrier potential. The further diffusion of the majority charge carriers is hindered by this potential barrier. But at the same time, the minority carriers can cross the junction as it is a downhill journey for them. When the minority charge carriers are generated thermally near the junction, they drift slowly along the junction plane, aided by the electric field of the barrier potential. This current, which arises because of the motion of the drift of minority charge carriers, is the drift current in a p-n junction diode. It flows in a direction opposite to the diffusion current
Diffusion current
-Introduction:Diffusion current is a current in a semiconductor caused by the diffusion of charge carriers . Diffusion current can be in the same or opposite direction of a drift current, that is formed due to the electric field in the semiconductor...
which arises owing to the motion of the majority charge carriers across the junction.
At equilibrium in an unbiased p-n junction diode, the diffusion current, which flows from the p to n region, is exactly balanced by the equal and opposite drift current.
In a biased p-n junction, the drift current is independent of the biasing, as the number of minority carriers is independent of the biasing voltages. But as minority charge carriers can be thermally generated, drift current is temperature dependent.
→ When an electric field is applied across the semiconductor material, the charge carriers attain a certain drift velocity Vd, which is equal to the product of the mobility of the charge carriers and the applied Electric Field intensity E;
Drift velocity Vd = mobility of the charge carriers × Applied Electric field intensity.
→ Holes move towards the negative terminal of the battery and electrons move towards the positive terminal of the battery. This combined effect of movement of the charge carriers constitutes a current known as "drift current" .
→ Drift current due to the charge carriers such as free electrons and holes is the current passing through a square centimeter area perpendicular to the direction of flow.
(i) Drift current density Jn, due to free electrons is given by
Jn = q n μn E (A / cm2)
(ii) Drift current density JP, due to holes is given by
JP = q p μp E (A / cm2)
Where, n - Number of free electrons per cubic centimeter.
P - Number of holes per cubic centimeter
μn – Mobility of electrons in cm2 / Vs
μp – Mobility of holes in cm2 / Vs
E – Applied Electric filed Intensity in V /cm
q – Charge of an electron = 1.6 × 10−19 coulomb.http://www.srmuniv.ac.in/downloads/drift_and_diffusion_currents.doc