An intrinsic semiconductor is a perfect semiconductor crystal with no impurities or lattice defects. There are no charge carriers at 0 K, in such materials, since the valence band is filled with electrons and the conduction band is empty. Electron-hole pairs are generated at higher temperatures as valence band electrons are excited thermally across the band gap to the conduction band. The only charge carriers in intrinsic material are these EHPs.
Intrinsic Material:
Visualizing the generation of EHPs in a quantitative way by considering the breaking of covalent bonds in the crystal lattice as shown in figure given below
If one of the Si valence electrons is broken away from its position in the bonding structure is a way that it becomes free to move in the lattice, a conduction electron is created and a broken bond is left behind.
To break the bond the energy required the bond is the band gap energy Eg.
The physical mechanism of EHP creation is evaluated by visualizing, but the energy band model is more productive for the purpose of quantitative calculation.
Difficulty with the broken bond model is that the free electron and the hole appear deceptively localized in the lattice.
The position of the free electron and the hole actually are spread out all over several lattice spacing and should be considered quantum mechanically by the probability distribution.
Since the electron and holes are created in pairs, the conduction band electron concentration n(electron per cm3)is equivalent to the concentration of holes in the valence band p (holes per cm3).
These intrinsic carrier concentrations are commonly referred to as ni.
There must be recombination of EHPs at the same rate at which they are generated, if a steady state carrier concentration is maintained.
When an electron in the conduction band makes a transition to an empty state in the valence band, recombination occurs, therefore annihilating the pair.
If we denote the generation rate of EHPs as gi (EHP/cm3-s) and the recombination rate as ri, equilibrium requires that, these rates are temperature dependent. For instance I (T) increases when the temperature is raised, and a new carrier concentration ni is established in a way that is higher recombination rate ri(T) just balances generation.
We can predict at any temperature that the rate of recombination of electron and hole ri is proportional to the equilibrium concentration of electrons n0 and the concentration of holes p0
The factor αr is a constant proportionality which depends on the particular mechanism by which recombination takes place.
Intrinsic Material:
Visualizing the generation of EHPs in a quantitative way by considering the breaking of covalent bonds in the crystal lattice as shown in figure given below
If one of the Si valence electrons is broken away from its position in the bonding structure is a way that it becomes free to move in the lattice, a conduction electron is created and a broken bond is left behind.
To break the bond the energy required the bond is the band gap energy Eg.
The physical mechanism of EHP creation is evaluated by visualizing, but the energy band model is more productive for the purpose of quantitative calculation.
Difficulty with the broken bond model is that the free electron and the hole appear deceptively localized in the lattice.
The position of the free electron and the hole actually are spread out all over several lattice spacing and should be considered quantum mechanically by the probability distribution.
Since the electron and holes are created in pairs, the conduction band electron concentration n(electron per cm3)is equivalent to the concentration of holes in the valence band p (holes per cm3).
These intrinsic carrier concentrations are commonly referred to as ni.
There must be recombination of EHPs at the same rate at which they are generated, if a steady state carrier concentration is maintained.
When an electron in the conduction band makes a transition to an empty state in the valence band, recombination occurs, therefore annihilating the pair.
If we denote the generation rate of EHPs as gi (EHP/cm3-s) and the recombination rate as ri, equilibrium requires that, these rates are temperature dependent. For instance I (T) increases when the temperature is raised, and a new carrier concentration ni is established in a way that is higher recombination rate ri(T) just balances generation.
We can predict at any temperature that the rate of recombination of electron and hole ri is proportional to the equilibrium concentration of electrons n0 and the concentration of holes p0
The factor αr is a constant proportionality which depends on the particular mechanism by which recombination takes place.
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