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Semiconductor - Coggle Diagram
Semiconductor
Intrinsic Semiconductor
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Electron-hole pairs can be generated through several mechanism such as thermal excitation, photon abrsorption and intrinsic defects
Thermal excitation: At finite temperatures, thermal energy can provide sufficient energy for covalent bonds to break, resulting in the generation of free electrons and holes.
The thermal energy causes some valence electrons to transition to the conduction band, leaving a positively charged hole in valence band
Photon absorption: When a photon is absorbed by the intrinsic semiconductor, it imparts sufficient energy to promote an electron from vaalence band to conduction band
This creates an electron-hole pair, where electron is in conduction band, and holes is in valence band
Intrinsic Defects: The defects such as vacancies or interstitial atoms can acts as energy levels within the bandgap.
If an electron from the VB gains enough enrgy to overcome the bandgap and is excited to one of these defect levels, it leaves behind a hole in VB.
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The DOS in an intrinsic semiconductor is characterized by a high density of states in VB, a lower density of states in CB, and extremely low density of states within the bandgap.
To determine the intrinsic carrier concentration (n0) in a semiconductor, need to be considered temperature (T) and energy bandgap (Eg) of material.
The intrinsic carrier concentration can be determine by using:
n0 = sqrt( Nc.Nv).exp(-Eg / (2kT))
where, n0 is intrinsic carrier concentration
Nc is effective density of states in CB
Nv is effective density of states in VB
Eg is energy bandgap of semiconductor
k is Boltzmann's constant (1.38 x 10^-23 J/K)
T is temperature in Kelvin
Extrinsic Semiconductor
A semiconductor that has been intentionally doped with impurities to modify its electrical properties
Electrons or holes are produced through the process of doping which involves intentionally introducing impurity atoms into the crystal lattice
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The DOS in VB remains relatively high, however due to doping, there may be additional impurity energy levels introduced within the bandgap.
Donor impurities, that introduces additional free electrons, creates energy closer to CB. The DOS in this region may show increased density of states for electrons
Acceptor impurities, that create additional holes, creates energy levels closer to VB. The DOS in this region may show increased density of states for holes
To determine the total number of electrons (N) in an extrinsic semiconductor, need to consider the doping concentration and volume of semiconductor material.
The total number of electrons can be calculated by using:
N = nV
where, n is doping concentration, which represents the number of impurity atoms per unit volume (cm-3)
V is volume of semiconductor material in which doping has occurred (cm-3)
