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In intrinsic crystalline silicon, there are approximately 5×10 22 atoms/cm 3. Doping concentration for silicon semiconductors may range anywhere from 10 13 cm −3 to 10 18 cm −3. Doping concentration above about 10 18 cm −3 is considered degenerate at room temperature. Degenerately doped silicon contains a proportion of impurity to ...
In an extrinsic semiconductor, the concentration of doping atoms in the crystal largely determines the density of charge carriers, which determines its electrical conductivity, as well as a great many other electrical properties. This is the key to semiconductors' versatility; their conductivity can be manipulated over many orders of magnitude ...
For example, doping pure silicon with a small amount of phosphorus will increase the carrier density of electrons, n. Then, since n > p, the doped silicon will be a n-type extrinsic semiconductor. Doping pure silicon with a small amount of boron will increase the carrier density of holes, so then p > n, and it will be a p-type extrinsic ...
When substituting a Si atom in the crystal lattice, four of the valence electrons of phosphorus form covalent bonds with the neighbouring Si atoms but the fifth one remains weakly bonded. If that electron is liberated, the initially electro-neutral donor becomes positively charged (ionised).
The SI unit of velocity is m/s, and the SI unit of electric field is V/m. Therefore the SI unit of mobility is (m/s)/(V/m) = m 2 /(V⋅s). However, mobility is much more commonly expressed in cm 2 /(V⋅s) = 10 −4 m 2 /(V⋅s). Mobility is usually a strong function of material impurities and temperature, and is determined empirically.
Silicon wafers are generally not 100% pure silicon, but are instead formed with an initial impurity doping concentration between 10 13 and 10 16 atoms per cm 3 of boron, phosphorus, arsenic, or antimony which is added to the melt and defines the wafer as either bulk n-type or p-type. [27]
The number density of the electron gas was assumed to be =, where Z is the effective number of de-localized electrons per ion, for which Drude used the valence number, A is the atomic mass per mole, [Ashcroft & Mermin 10] is the mass density (mass per unit volume) [Ashcroft & Mermin 10] of the "ions", and N A is the Avogadro constant.
The molten zone carries the impurities away with it and hence reduces impurity concentration (most impurities are more soluble in the melt than the crystal). Specialized doping techniques like core doping , pill doping, gas doping and neutron transmutation doping are used to incorporate a uniform concentration of desirable impurity.