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Electronic Materials

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    Pritam G

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A brief introduction to Electronic Materials and Semiconductors

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    Electronic Materials
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    Atomic Structure of Conductors Valence Electron The atomic structures of good conductors usually have only one electron in their outer most shell That electron is easily stripped off the atom because the resulting ion will have stable electronic configuration This stripped off electron will then result in the flow of current Easily Freed for Current Flow 11 29+ Copper Atom
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    Atomic Structure of Semiconductors The main characteristic of semiconductor atoms if that they have 4 electrons in their outer most (valence) shell So the atom can either gain 4 electrons or lose 4 electrons to attain stable electronic configuration Note: 4 Valence Electrons 14+ Silicon
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    Structure of Insulators Most insulators are compound of several elements The atoms are tightly bound to one another. So electrons are difficult to strip away. So insulator are poor conductors
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    Why the difference? Conduction band Band Gap AE 322 ev Fermi energy Valence band Metals Semiconductors Insulators
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    Continued Valence band: Valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature(outermost electron orbital which is occupied by electrons) Conduction band: conduction band is the lowest range of vacant electronic states Band gap: It is the energy difference between the top of the valence band and the bottom of the conduction band When sufficient energy is supplied electrons jump from the valence band to the conduction band by overcoming the band gap and thus resulting in the flow of current
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    Crystal Lattice Structure The unique capability of semiconductor atoms is their ability to link together to form a physical structure called a crystal lattice. Nucleus of Atoms The atoms link together with one another sharing their outer electrons. These links are called covalent bonds Outer Orbit or Valence Shell no Covalent Bonds Si doo• Electrons Si = Silicon Nucleus with 14 Protons
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    3D Crystal Lattice Structure Silicon Atoms Covalent Bonds Imaginary Cube This structure is known as the diamond cubic crystal structure.
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    Semiconductors can be Insulators If the material is pure semiconductor material like silicon, the crystal lattice structure forms an excellent insulator since all the atoms are bound to one another and are not free for current flow, Good insulating semiconductor material is referred to as intrinsic. Since the outer valence electrons of each atom are tightly bound together with one another, the electrons are difficult to dislodge for current flow. Silicon in this form is a great insulator. Semiconductor material is often used as an insulator,
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    Doping To make the semiconductor conduct elec.Crjcj-CY, other atoms called impurities must be added, "Impurities" are different elements, This process is called doping,
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    Semiconductors can be Conductors An impurity, or element like arsenic, has 5 valence electrons, Adding arsenic (doping) will allow four of the arsenic valence electrons to bond with the neighboring silicon atoms, The one electron left over for each arsenic atom becomes available to conduct current flow. Nucleus of Atoms opp Outer Orbit or Valence Shell Extra Electron for Current Flow Arsenic Atom
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    Types of Semiconductor Materials The silicon doped with extra electrons is called an "N type" semiconductor. "N" is for negative, which is the charge of an electron. Silicon doped with material missing electrons that produce locations called holes is called "P type" semiconductor. "P" is for positive, which is the charge of a hole.

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