Consider two Si semiconductors samples A and B samples A has

Consider two Si semiconductors samples A and B, samples A has its Felin: energy level Eg18 above E_F: sample B has its Felin: energy level Eg18 below E_F: Assume T = took, n: = 1.5 times 10^10 cm^-3, kT = 0.026, Eg 1.12 Sample A doped with a single type of imentity, determine nc, p_01 and doping density Sample is doped with a single type of imentity, determine p_0, no, doping density What type of density of impilities need to be added to sample so if has same p_0 as A

Solution

It is possible to shift the balance of electrons and holes in a silicon crystal lattice by \"doping\" it with other atoms.

Atoms with one more valence electron than silicon are used to produce \"n-type\" semiconductor material. These n-type materials are group V elements in the periodic table, and thus their atoms have 5 valence electrons that can form covalent bonds with the 4 valence electrons that silicon atoms have. Because only 4 valence electrons are needed from each atom (silicon and n-type) to form the covalent bonds around the silicon atoms, the extra valence electron present (because n-type materials have 5 valence electrons) when the two atoms bond is free to participate in conduction. Therefore, more electrons are added to the conduction band and hence increases the number of electrons present.

Atoms with one less valence electron result in \"p-type\" material. These p-type materials are group III elements in the periodic table. Therefore, p-type material has only 3 valence electrons with which to interact with silicon atoms. The net result is a hole, as not enough electrons are present to form the 4 covalent bonds surrounding the atoms. In p-type material, the number of electrons trapped in bonds is higher, thus effectively increasing the number of holes. In doped material, there is always more of one type of carrier than the other and the type of carrier with the higher concentration is called a \"majority carrier\", while the lower concentration carrier is called a \"minority carrier.\"

In a typical semiconductor there might be 10¹⁷cm^-3 majority carriers and 10⁶cm^-3 minority carriers. Expressed in a different form, the ratio of minority to majority carriers is less than one person to the entire population of the planet. Minority carriers are created either thermally or by incident photons.