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From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Silicon is the most important semiconductor in todays electronics
|SOURCE: Courtesy of IBM
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
200 mm and 300 mm Si wafers.
|SOURCE: Courtesy of MEMC, Electronic Materials, Inc.
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
GaAs ingots and wafers. GaAs is used in high speed electronic devices, and optoelectronics.
|SOURCE: Courtesy of Sumitomo Electric Industries, Ltd.
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
(a) A simplified two-dimensional illustration of a Si atom with four hybrid orbitals hyb. Each orbital has one electron. (b) A simplified two-dimensional view of a region of the Si crystal showing covalent bonds. (c) The energy band diagram at absolute zero of temperature.
Fig 5.1
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
A two-dimensional pictorial view of the Si crystal showing covalent bonds as two lines where each line is a valence electron.
Fig 5.2
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
(a) A photon with an energy greater than Eg can excite an electron from the VB to the CB. (b) When a photon breaks a Si-Si bond, a free electron and a hole in the Si-Si bond is created.
Fig 5.3
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Thermal vibrations of atoms can break bonds and thereby create electron-hole pairs.
Fig 5.4
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
A pictorial illustration of a hole in the valence band wandering around the crystal due to the tunneling of electrons from neighboring bonds.
Fig 5.5
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Electron and Hole Drift Velocities vde = eEx and vdh = hEx
vde = drift velocity of the electrons, e = electron drift mobility, Ex = applied electric field, vdh = drift velocity of the holes, h = hole drift mobility
Conductivity of a Semiconductor
= ene + eph
= conductivity, e = electronic charge, n = electron concentration in the CB, e = electron drift mobility, p = hole concentration in the VB, h = hole drift mobility
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Mass Action Law
Eg np = n = N c N v exp kT n = intrinsic concentration
2 i
i
The np product is a constant, ni2, that depends on the material properties Nc, Nv, Eg, and the temperature. If somehow n is increased (e.g. by doping), p must decrease to keep np constant.
Mass action law applies in thermal equilibrium and in the dark (no illumination)
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Energy band diagrams for (a) Intrinsic, (b) n-type, and (d) p-type semiconductors. In all cases, np = ni2
Fig 5.8
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Arsenic-doped Si crystal. The four valence electrons of As allow it to bond just like Si, but the fifth electron is left orbiting the As site. The energy required to release the free fifth electron into the CB is very small.
Fig 5.9
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Energy band diagram for an n-type Si doped with 1 ppm As. There are donor energy levels just below Ec around As+ sites.
Fig 5.10
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
n-Type Conductivity
ni = eN d e + e N d
h eN d e
= electrical conductivity
e = electronic charge Nd = donor atom concentration in the crystal
e = electron drift mobility, ni = intrinsic concentration, h = hole drift mobility
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Boron-doped Si crystal. B has only three valence electrons. When it substitutes for a Si atom, one of its bonds has an electron missing and therefore a hole, as shown in (a). The hole orbits around the B- site by the tunneling of electrons from neighboring bonds, as shown in (b). Eventually, thermally vibrating Si atoms provide enough energy to free the hole from the B- site into the VB, as shown.
Fig 5.11
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Energy band diagram for a p-type Si doped with 1 ppm B. There are acceptor energy levels Ea just above Ev around B- sites. These acceptor levels accept electrons from the VB and therefore create holes in the VB.
Fig 5.12
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
(a) Below Ts, the electron concentration is controlled by the ionization of the donors. (b) Between Ts and Ti, the electron concentration is equal to the concentration of donors since They would all have ionized. (c) At high temperatures, thermally generated electrons from the VB exceed the number of Electrons from ionized donors and the semiconductor behaves as if intrinsic.
Fig 5.14
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
The temperature dependence of the electron concentration in an n-type semiconductor.
Fig 5.15
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
The temperature dependence of the intrinsic concentration
Fig 5.16
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Scattering of electrons by an ionized impurity.
Fig 5.17
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
The variation of the drift mobility with dopant concentration in Si for electrons and holes at 300 K.
Fig 5.19
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
Schematic illustration of the temperature dependence of electrical conductivity for a doped (n-type) semiconductor.
Fig 5.20
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap ( McGraw-Hill, 2005)
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