![Doping
Doping is the incorporation of [substitution] impurities into a
semiconductor according to our requirements.
In other words, impurities are introduced in a controlled
manner
Impurities change the conductivity of the material so that it
can be fabricated into a device
Doped crystals are extrinsic semiconductors. adding minute
amounts of suitable impurities to the pure crystals
Crystals are doped to be n type or p type
n type semiconductors have few minority carriers (holes).
p type semiconductors have few minority carriers (electrons).](https://image.slidesharecdn.com/ecx52391n-130310124256-phpapp01/85/Ecx-5239-1n-11-320.jpg)
![probability of occupation
The Fermi level or Fermi energy is the energy, at which the
probability of occupation by an electron (or hole) is exactly 遜. In
semiconductor, usually, Fermi level is in the band gap.
F(E )=1 1+exp[(E-EF) /KT ]
Where
K = Boltzmann constant
E F =Fermi energy or Fermi level
T =0k
F(E)=The probability that an electron state having
energy E is occupied](https://image.slidesharecdn.com/ecx52391n-130310124256-phpapp01/85/Ecx-5239-1n-13-320.jpg)
![=1/1+exp [(0.4/0.026)]
= 2.08*10 -7
EA- EF ={EF-EV-(EA-E V)}
= 0.15-0.04
= -0.11eV](https://image.slidesharecdn.com/ecx52391n-130310124256-phpapp01/85/Ecx-5239-1n-14-320.jpg)
![PROBABILITY OF ACCEPTER STATES
F(EA)=1 1+exp[(EA-EF) /KT ]
=1/1+exp [(-0.11/0.026)]
= 0.9856](https://image.slidesharecdn.com/ecx52391n-130310124256-phpapp01/85/Ecx-5239-1n-15-320.jpg)
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Ecx 5239 1n
- 1. PHYSICAL ELECTRONICS ECX 5239 PRESENTATION 01 G.V.I.S.SILVA 709062591 2012-12-15
- 2. Why is the conductivity of insulators negligible, compared to semiconductor ? It depends on mainly two factors , conductivity Atomic bond Energy band structure
- 3. conductivity Insulator semiconductor valence electrons are tightly Mostly covalent bonding bound to (or shared with) the somewhat weaker bonding individual atoms strongest ionic Electrons can reach the (partially covalent) bonding. conduction band at ordinary temperatures. The energy gap is too large when An electron promoted into the compared to semiconductor. conduction band leaves a Hole (positive charge) in the valence band, that can also participate in conduction., The conductivity increases with increasing temperature.
- 4. ATOMIC BONDING Insulator VS Semiconductor
- 5. The highest filled state at 0 K Fermi Energy (EF) Band structure The two highest energy bands The energy difference are: between the bottom of the Valence band the highest band Conduction and the top of where the electrons are present at 0 the Valence bands is called K the Band Gap Conduction band - a partially filled or empty energy band where the electrons can increase their energies by going to higher energy levels within the band when an electric field is applied
- 6. Band model Insulators: Semiconductors: wide band gap (> 2 eV) narrow band gap (< 2 eV)
- 7. When enough energy is supplied to the e- sitting at the Empty top of the valance band, e- can conduction make a transition to the bottom band of the conduction band. When electron makes such a transition it leaves behind a missing electron state. This missing electron state is called as a hole. Hole behaves Energy e- e- e- e- + + + + as a positive charge carrier. Full Magnitude of its charge is the valance band same with that of the electron but with an opposite sign.
- 8. Electron mobility Characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field, in semiconductors . When an electric field E is applied across a piece of material, the electrons respond by moving with an average velocity called the drift velocity V, Then the electron mobility 亮 is defined as |v| = 亮E
- 9. Vd E E: applied field : mobility of charge carrier cm 刻 2 Vd is a proportionality factor 緒 V Sec E So is a measure how easily charge carriers move under the influence of an applied field or determines how mobile the charge carriers are.
- 10. How mobility depend on doping? Mobility is dependent on the drift velocity. The main factor determining drift velocity (other than effective mass) is scattering time. How long the carrier is accelerated by the electric field until it scatters (collides) with something that changes its direction and/or energy. The most important sources of scattering in typical semiconductor materials, discussed below, are ionized impurity scattering.
- 11. Doping Doping is the incorporation of [substitution] impurities into a semiconductor according to our requirements. In other words, impurities are introduced in a controlled manner Impurities change the conductivity of the material so that it can be fabricated into a device Doped crystals are extrinsic semiconductors. adding minute amounts of suitable impurities to the pure crystals Crystals are doped to be n type or p type n type semiconductors have few minority carriers (holes). p type semiconductors have few minority carriers (electrons).
- 12. The purpose of semiconductor doping is to increase the number of free charges that can be moved by an external applied voltage.. So the crystal has no resistance to current flow and behaves as a superconductor. The perfect periodic potential does not impede the movement of the charge carriers. However, in a real device or specimen, the presence of impurities, interstitials, subtitionals, temperature , etc. creates a resistance to current flow.
- 13. probability of occupation The Fermi level or Fermi energy is the energy, at which the probability of occupation by an electron (or hole) is exactly 遜. In semiconductor, usually, Fermi level is in the band gap. F(E )=1 1+exp[(E-EF) /KT ] Where K = Boltzmann constant E F =Fermi energy or Fermi level T =0k F(E)=The probability that an electron state having energy E is occupied
- 14. =1/1+exp [(0.4/0.026)] = 2.08*10 -7 EA- EF ={EF-EV-(EA-E V)} = 0.15-0.04 = -0.11eV
- 15. PROBABILITY OF ACCEPTER STATES F(EA)=1 1+exp[(EA-EF) /KT ] =1/1+exp [(-0.11/0.026)] = 0.9856
- 16. Donors
- 17. Accepter
- 19. Thank you!