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In solid-state physics, the electron mobility characterises how quickly an electron can move through a metal or semiconductor when pushed or pulled by an electric field. There is an analogous quantity for holes, called hole mobility. The term carrier mobility refers in general to both electron and hole mobility.
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- Definition of Electrical Mobility of Electrons
- Formula of Mobility of Charge Carriers
- Unit of Mobility
- Dimension of Mobility of Electron
- Mobility of Free Electrons in Semiconductors and Conductors
- Mobility of Holes in A Semiconductor
- Why Is The Mobility of Free Electrons Greater Than The Mobility of Holes?
The charge carriers move by the influence of an external electric field. So, due to the application of an electric field charge carriers will get somedrift velocity to move in the conductors or the Semiconductors. Electrical mobilityof charge carriers is defined as the drift velocity of the carriers per unit applied electric field.
Now, what is the electron mobility formula? Let, after applying an external electric field E, the charge carriers get the drift velocity V.Then the formula for the mobility of the charge carriers is, μ=VE\small {\color{Blue} \mu =\frac{V}{E}}μ=EV..(1) This is the formula of mobility of charge carriers. This is also the electron mobility formula.
The SI unit of drift velocity is m/s and the SI unit of the electric field is V/m. So, the SI unit of Mobility is m2/V.s
Drift velocity has the dimension of [LT-1] and the dimension of electric field is [MLT-3I-1]. Then the dimensional formula of mobility of charges is [M-1T2I].
Free electrons move in the conduction band. The mobility of the electron is thedrift velocity of the electronin presence of a unit amount of electric field. One can get the mobility of electrons both in conductors and semiconductors. The value of Electron mobility is different in different materials.
We all know that there is no hole in a conductor. So, hole mobility is applicable only for semiconductors. Sometimes it is called semiconductor mobility. Mobility of holes is their ability to move in a semiconductor in presence of an external electric field. The value of the mobility of holes in crystalline silicon is 450 cm2/V.s.
Holes are not the physical objects. They are the absence of electrons. So, the movement of holesis nothing but the movement of electrons in the opposite direction. Now, free electrons move in the conduction band and the holes move in the valance band. Now, the binding force of the nucleus on free electrons is smaller than that on the holes (or vale...
The SI unit of electric field is V/m, and the SI unit of velocity is m/s. Thus, the SI unit of mobility is m2/ (V.s). Hole mobility. The ability of an hole to move through a metal or semiconductor, in the presence of applied electric field is called hole mobility. It is mathematically written as.
There are two types of mobile charges in semiconductors: electrons and holes. In an intrinsic (or undoped) semiconductor electron density equals hole density. Semiconductors can be doped in two ways: N-doping: to increase the electron density P-doping: to increase the hole density . Thermal Motion of Electrons.
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1. Thermal Motion. In thermal equilibrium, carriers are not sitting still: Undergo collisions with vibrating Si atoms. (Brownian motion) Electrostatically interact with each other and with ionized (charged) dopants. Characteristic time constant of thermal motion: ⇒ mean free time between collisions. c τ ≡. collison time [s]
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Motion and Recombination of Electrons and Holes. CHAPTER OBJECTIVES. The first chapter builds the necessary model for understanding semiconductors at equilibrium. This chapter will consider how the electrons and holes respond to an electric field and to a gradient in the carrier concentration.
The number of electrons and holes in an intrinsic semiconductor are equal. However, both carriers do not necessarily move with the same velocity with the application of an external field. Another way of stating this is that mobility is not the same for electrons and holes. Semiconductor Impurities
