ECE 231 -12

ECE 231 -12 - ECE-231 Circuits and Systems I Spring 2011...

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Unformatted text preview: ECE-231 Circuits and Systems I Spring 2011 Session 11 Professor Stewart Personick Office: ECEC Room 321 Stewart.Personick@NJIT.edu Semiconductor-based Electronic Devices: Diodes and Transistors Semiconductors Conceptual 2-dimensional representation of crystalline Silicon (Si). Each Si atom has 4 electrons in its outer shell. Each Si atom shares 1 of these 4 electrons with its 4 nearest neighbors (covalent bond) . Semiconductors + At any temperature above absolute zero, there will be a small percentage of electrons that gain enough thermal energy to break their covalent bonds, and to roam freely within the silicon crystal. This results in a negatively charged free electrons, and positively charged silicon ions (holes). e Semiconductors + At any temperature above absolute zero, there will be a small percentage of electrons that gain enough thermal energy to break their covalent bonds, and to roam freely within the silicon crystal. This results in a negatively charged free electron, and positively charged silicon ions (holes). If an electron from a silicon atom that is (for example ) to the right of a hole (i.e. to the right of a silicon atom with a missing electron) jumps to the left to fill the hole then this results in the hole moving to the right e Semiconductors + e At any temperature above absolute zero, there will be a small percentage of electrons that gain enough thermal energy to break their covalent bonds, and to roam freely within the silicon crystal. This results in a negatively charged free electron, and positively charged silicon ions (holes). If an electron from a silicon atom that is (for example ) to the right of a hole (i.e. to the right of a silicon atom with a missing electron) jumps to the left to fill the hole then this results in the hole moving to the right Semiconductors If one substitutes an atom that has 5 electrons in its outer shell for a silicon atom then (at temperatures well above absolute zero, e.g. room temperature) it is highly probable that the extra electron associated with that atom will break free and roam freely within the crystal. Examples of such donor atoms are: nitrogen (N), phosphorus (P) and arsenic (As). It is easy for these donated electrons to move around within the crystal. It is very unlikely that any of the positively charged donor atoms (that the donated electrons leave behind) will recapture an electron from a neighboring neutral silicon atom; and if one did, it would quickly give up that recaptured electron....
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ECE 231 -12 - ECE-231 Circuits and Systems I Spring 2011...

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