Lecture3_Introduction2Semiconductors

Lecture3_Introduction2Semiconductors - Lecture Lecture 3...

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ecture Lecture 3 Introduction to Semiconductors and Energy Bandgaps ECE 4833 - Dr. Alan Doolittle Georgia Tech
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Solar Cells Why do the electrons flow hen light is when light is present but not flow when light t t ? is not present? Answer, Energy Bandgap (very important ncept). ECE 4833 - Dr. Alan Doolittle Georgia Tech concept).
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Classifications of Electronic Materials • or metals, the electrons can jump from the valence orbits (outermost core energy levels of the atom) to any For metals, the electrons can jump from the valence orbits (outermost core energy levels of the atom) to any position within the crystal (free to move throughout the crystal) with no “extra energy needed to be supplied” •For insulators, it is VERY DIFFICULT for the electrons to jump from the valence orbits and requires a huge amount of energy to “free the electron” from the atomic core. •For semiconductors, the electrons can jump from the valence orbits but does require a small amount of energy to th l t ” f th t i ECE 4833 - Dr. Alan Doolittle Georgia Tech “free the electron” from the atomic core.
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Classifications of Electronic Materials • emiconductor materials are a sub- ass of materials distinguished by the existence of a range of disallowed Semiconductor materials are a sub class of materials distinguished by the existence of a range of disallowed energies between the energies of the valence electrons (outermost core electrons) and the energies of electrons free to move throughout the material. •The energy difference ( energy gap or bandgap ) between the states in which the electron is bound to the atom and when it is free to conduct throughout the crystal is related to the bonding strength of the material, it’s density, d f i i it f th b d d th h i t l t d t th l f b di ECE 4833 - Dr. Alan Doolittle Georgia Tech the degree of ionicity of the bond, and the chemistry related to the valence of bonding. •High bond strength materials (diamond, SiC, AlN, GaN etc. ..) tend to have large energy bandgaps. •Lower bond strength materials (Si, Ge, etc. ..) tend to have smaller energy bandgaps.
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Classifications of Electronic Materials •More formally, the energy gap is derived from the Pauli exclusion principle, where no two electrons occupying the same space, can have the same energy. Thus, as atoms are brought closer towards ne another and begin to bond one another and begin to bond together, their energy levels must split into bands of discrete levels closely spaced in energy they so closely spaced in energy, they can be considered a continuum of allowed energy. •Strongly bonded materials tend to have small interatomic distances between atoms. Thus, the strongly bonded materials can have larger ECE 4833 - Dr. Alan Doolittle Georgia Tech energy bandgaps than do weakly bonded materials.
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Material Classifications based on Bonding Method onds can be classified as metallic Ionic Covalent and van der Waals Bonds can be classified as metallic, Ionic, Covalent, and van der Waals.
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Lecture3_Introduction2Semiconductors - Lecture Lecture 3...

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