There are similarities and differences between the flow of mobile charges in metals and semiconductors.
Basically, as a first answer, it is clear that the basic difference is that current is conducted in semiconductors using two types of carriers, holes and electrons, while in metals there are only electrons. holes and electrons flow in opposite directions under the influence of an electric field. In metals and semiconductors circuits, electrons are sourced by the negative part of the battery source, while in semiconductors the negative terminals will supply electrons to combine with holes attracted to it as well as to further cater for the electrons. Batteries after all only generate electrons.
Intrinsic semiconductor is closer to an insulator because of the low concentration of free electrons or holes. On the other hand, a doped semiconductor is close to a metal in that current is conducted mainly by one carrier (the majority carrier) with higher conductivity than the intrinsic semiconductor.
Increasing the temperature of metals results in that the free electrons collisions with the crystal lattice resulting in increased resistance (less conductivity), while in semiconductors, increasing the temperature increases generation of electron-hole pairs resulting in increased conductivity (decreased resistance), which is opposite to metals.
In metals the increased EMF results in increased current and the failure of a metal link will occur due to a melt down due to increased heat loss (I2R), while in semiconductors the failure can also be due due to excessive generation of carriers and current multiplication (Avalanche breakdown). In this way, semiconductors are different to metals and more similar to insulators that break in a similar way.
I think others have more to say. Thanks. @AlDmour.
In metals the only carriers are electrons so if we want to have a look at similarities we have to compare the transport of electron in metal and semiconductors. The flow of electron in metal is described from the Drude Model. (http://www.colorado.edu/physics/phys4340/phys4340_sp09/notes/Drude%20notes.pdf)
In a semiconductor because of the energy bandgap the electron can flow only if they receive a sufficient energy to overcome the energy bandgap becoming available in the conduction band. Once they are the conduction band they can travel in the same way the do in the metal case. The contribution to the current is different because in semiconductor there is a gradient of the carrier that can be added up to the contribution due to the electric field.
I would like to thank the colleagues who liked my question and my colleagues who introduced an answer to my question. They covered some important points in the flow of charge carriers in metals and semiconductor.
At the beginning, it is helpful to introduce the types of current of mobile charge carriers. There are three types of current: the convection current, the conduction current and the diffusion current.
- The convection current. It can be expressed by I= Aqnv where A the cross sectional area, q the electron charge. v its velocity and n the density of mobile charge carriers
- The conduction current which is developed in a metal or a semiconductor on the application of an electric field E. It can be expressed by: I= AqnuE=Asigma E, with u the mobility of the mobile charge carrier in the solid state material and sigma the conductivity of the material. Upon the application of the electric field on a metal or a semiconductor the mobile charge carriers drift to a steady state velocity v = uE. This is because of the scattering of the mobile carriers in their motion in the solid material. Scattering constitutes an impeding frictional force. Here, the mobile charge carriers will be in a thermal random motion before the application of the electric field and the electric field will partly order them resulting in the drift velocity.
-The last type of current of mobile charge carriers is the diffusion current. The diffusion current is caused by the presence of concentration gradients of thermal randomly moving particles like the gas particles, electrons and holes. All these particles move randomly because of their thermal energy. These particles will be driven down the concentration gradient. This current can be expressed by I= A q D ( dn/dx) where D is the diffusion constant and dn/dx is the concentration gradient.
In the metals electron gradients can not last for times greater than the very small dielectric relaxation time.
In semiconductors concentration gradients can exist because of the doping concentration change with position, so called doping profiles, as well as minority Carrier excess can last relatively large times before they disappear by recombination. Minority carriers flow by diffusion in bipolar devices especially under low injection condition.
Thank you and sorry for long answer
My Question is almost relates to this question. But if you absorbed the following video http://www.youtube.com/watch?v=NInt1Ss3vQ4 , if the plates of the capacitor is of conductor only then why the conductors have both charges i.e +ve and -ve charges.In short I want to know why the plates of capacitor which in not connected to any source have both charges +ve and -ve Charges.
http://www.youtube.com/watch?v=NInt1Ss3vQ4
Dear Mahendranth,
The materials are composed of atoms which are electrically neutral. Every electron has always its neutralizing positive charge in its parent atomic core. While the valence electrons in the metal are free to move inside metal, their neutralizing positive ion cores are fixed in the lattice. So, a metal can be charged by either negative electron charges or positive ion core charges at its surface according to the polarity of the metallic plate in the capacitor.
Wish you success.
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