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Explain the following giving suitable examples : (i) Mode of conduction in n-type semiconductors and p -type semiconductors. (ii) Anisotropy in crystalline solids

Explain the following giving suitable examples :
(i) Mode of conduction in n-type semiconductors and p -type semiconductors.
(ii) Anisotropy in crystalline solids

Grade:Upto college level

1 Answers

Sunil Kumar FP
askIITians Faculty 183 Points
9 years ago
N-Type semiconductor is created by adding pentavalent impurities likePhosphorus(P),Arsenic(As), orAntimony(Sb). The purpose of doing so is to make more charge carriers, orelectronsavailable in the material for conduction.Semiconductor materials like Silicon and Germanium have four electrons in their outer shell (valence shell). All the four electrons are used by the semiconductor atom in forming bonds with its neighbouring atoms, leaving a low number of electrons available for conduction. Pentavalent elements are those elements which have five electrons in their outer shell. When pentavalent impurities like Phosphorus or Arsenic are added into semiconductor, four electrons form bonds with the surrounding silicon atoms leaving one electron free. The resulting material has a large number of free electrons. Since electrons are negative charge carriers, the resultant material is called N-type (or negative type) semiconductor. The pentavalent impurity that is added is called 'Dopant' and the process of addition is called 'doping'.

ptype semiconductor
when adoped semiconductor contains mostly holes it is called p type semiconductorAs opposed to n-type semiconductors, p-type semiconductors have a larger hole concentration than electron concentration. The phrase 'p-type' refers to the positive charge of the hole. In p-type semiconductors, holes are the majority carriers and electrons are the minority carriers. P-type semiconductors are created by doping an intrinsic semiconductor with acceptor impurities (or doping a n-type semiconductor). A common p-type dopant for silicon is boron. For p-type semiconductors the Fermi level is below the intrinsic Fermi level and lies closer to the valence band than the conduction band.

(2)crystalline solid are anisotropic that is some of their properties like electrical resistance or refractive index show different value when measured along different direction in the same crystals

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