LDR notes

Topics: Diode, P-n junction, Semiconductor Pages: 2 (1164 words) Published: October 22, 2014

The diode – A diode is an electronic component which allows electric current to glow in only one direction. Diodes are constructed from semiconductors. The anode is the positive terminal and the cathode the negative terminal. LED= light emitting diode a diode which emits light.

Semiconductor materials
Silicon is the most commonly used semiconductor in electronics, germanium is also used. These elements form a stable crystal lattice, with each atom sharing its four outer electrons (called valence electrons) with neighbouring atoms. Silicon is a poor conductor because the outer electrons in each atom are held firmly in place by the crystalline structure. Doping

Doping is a method used to increase the conductivity of a semiconductor by adding tiny impurities to the crystal lattice. A very small proportional of silicon atoms are replaced with atoms of other elements. Two way of doping.

N-type semiconductor Use atoms with five outer electrons (antimony, arsenic or phosphorus). While four of these outer electrons fit into the crystalline structure, the fifth does not, and is free to move. The negatived charged electron is about to move. The semiconductor doped in this way is still electrically neutral, since the impurity atom has an extra proton in the nucleus to balance its extra electron. P-type semiconductor There are only three outer electrons (aluminium, boron, gallium or indium), which leave a ‘hole’ in the crystalline structure where an electron is ‘missing’. Nearby electrons are able to ‘jump’ into this hole, leaving behind a positively charged silicon atom. It’s called p-type semiconductor because the moving hole has the effect of a positive charge moving through the lattice. A semiconductor doped in this way is still electrically neutral, since the impurity atom contains one less proton in the nucleus to account for the absence of one electron. Both n-type and p-type semiconductors contain sufficient free electrons to form good...
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