This presentation explains the band structure, intrinsic semiconductor, extrinsic semiconductor, electrical conductivity, mobility, hall effect, p-n junction diode, tunnel diode and optical properties of the semiconductor.
5. ⢠Electron and holes (free carriers) in intrinsic semiconductor are
produced due to temperature and the carriers follow the Fermi-Dirac
distribution function,
đ đ¸ =
1
đ
(đ¸âđ¸ đš)
đ đľ đ + 1
where đ đ¸ is probability density function for concentration of
electrons at temperature T.
Fig. : The Fermi-Dirac distribution function.
6. Extrinsic Semiconductors
Fig. : The electronic bonds in Si crystal doped with Boron B (p type semiconductor)
and Silicon crystal doped with Arsenic As (n type semiconductor).
7. Electrical conductivity and Mobility
⢠Electrical conductivity is the measure of a material's ability to allow
the transport of an electric charge.
đđ =
đđ2
đ đ
đ đ
đđ â 1 đ¨đ â1is a typical figure in semiconductor.
⢠The electron mobility đ đis the drift velocity electron per unit field
strength and measure of the rapidity or swiftness of the motion of
electron in the field.
đ đ =
đđ đ
đ đ
8. Hall Effect
The Hall effect is the production of a voltage difference (the Hall voltage) across
an electrical conductor, transverse to an electric current in the conductor and to
an applied magnetic field perpendicular to the current.
Hall voltage đđť =
đź đĽ đľ đ§
đđĄđ
Hall coefficient đ đť =
đ¸ đť
đ˝ đĽ đľ đ§
= â
1
đđ
9. Applications of Hall effect:
⢠The sign of charge carriers,
⢠The number of charge carriers per unit volume,
⢠Mobility of charge carriers,
⢠The unknown magnetic field if the hall voltage (VH) is known.
11. ⢠Shockley Diode equation,
đź = đźđ đ
đ đˇ
đđ đâ1
I : diode current,
đźđ : reverse bias saturation current,
đđˇ:voltage across the diode,
đđ:thermal voltage kT/q = 25.85mV at 300K and,
đ : ideality factor (between 1 and 2)
12. Tunnel Diode
⢠A Tunnel diode is a heavily doped p-n junction diode in which the
electric current decreases as the voltage increases.
⢠Width of the depletion region in tunnel diode is very narrow due to
high amount of impurities in semiconductor.
⢠In tunnel diode, electric current is caused by âTunnelingâ.
15. Optical properties of semiconductor: Absorption
⢠The Fundamental Absorption process:
16. ⢠The Exciton absorption:
The energy of the photon involved in exciton absorption is
âđ = đ¸đ â đ¸đđĽ
where đ¸đđĽ (about 0.01 eV)is the exciton binding energy.
Fig. : The exciton level and associated absorption.
17. Photoconductivity
⢠When an incident light having energy âđ > đ¸đ,is incident upon a
semiconductor causes an increase in the electrical conductivity, This
phenomena is called Photoconductivity.
Fig. : Basic experimental setup for photoconductivity.