Understanding the light-emitting diode principle, first of all to understand the basic knowledge of the semiconductor.
Conductive properties of semiconductor materials between conductor and insulator material, it is unique in: when the semiconductor stimulation by external conditions of light and heat, its conductive ability significant change will happen;
Add trace impurities in pure semiconductor, its conductive ability will also increase significantly.
Is used most in modern electronics semiconductor silicon (
And germanium (
The outermost electrons, they are 4, when silicon or germanium atoms crystal adjacent atoms interact with each other, make the outer electrons into a total of two atoms, which form the covalent bonds in the crystal structure, it is a kind of constraint ability small molecular structure.
At room temperature (
Cases, due to the thermal excitation can make some of the most outer layer of the electrons gain enough energy and become free electrons out of covalent bonds, this process is called intrinsic excitation.
Becoming free electrons in the electronic slip the leash, covalent bond will leave a space, the space is called a hole, the hole is an important characteristics of semiconductor is distinguished from a conductor.
< / p> due to the covalent bonds appeared holes, under the effect of the applied electric field or other energy, nearby the valence electrons will fill the hole, and the original position of the electron to form a new hole, other electronic transfer again on the new hole.
The result is a certain amount of charge transfer this sign we can use the following formula calculated the concentration of free electrons in the semiconductor: < / p> I (
= AT3/2 e - EG / 2 kt type, < / p> EG -
The energy needed to power a electronic to break free from the shackles of covalent bond, the unit is eV (
, also known as the forbidden band width;
< / p> T -
< / p> k -
The boltzmann constant (
< / p> e -
The natural logarithm of the bottom.
< / p> because of the free electrons and holes in the intrinsic semiconductors come in pairs, so this formula can also be used to represent the concentration of the hole.
Free electrons in the semiconductor
Or a hole)
, the higher the concentration of the conductive ability is strong, near room temperature and higher temperature every 8 ℃, silicon free electron density increases 1 times;
Temperature rise every 12 ℃, germanium concentration of free electrons increases 1 times.
< / p> add a small amount of pentavalent in intrinsic semiconductor impurity elements such as phosphorus, it is with other semiconductor atoms form a covalent bond will have a redundant electronics, this excess electron only need very little energy can get rid of the shackles as free electrons, such impurities are called electronic semiconductor semiconductor (
N type semiconductor)
The intrinsic semiconductor to add a small amount of impurity elements (
Such as boron, etc. )
, because it only three outer electronics, semiconductor of atoms around with covalent bond can produce a vacancy in the crystal, after this kind of impurity of semiconductor is called the cavity semiconductor (
P type semiconductor)
After the n-type and p-type semiconductor combination, on the border of them will appear the concentration of free electrons and holes, so all the electrons and holes to spread to a region of low concentration, leaves some charged ions can't move, undermining the N and P original electrically neutral.
They can't move of charged particles are often referred to as space charge, they focused on the N and P near the interface forms a very thin space charge region, this is what we call the p-n junction.
< / p> at the ends of the PN junction with positive bias voltage (
One side of the P type plus positive voltage)
After the hole and free electrons can move each other, form a electric field.
Then new injection holes and free electrons to composite, composite and sometimes excess energy released in the form of photons, which is LED light that we see.
The spectral range is relatively narrow, due to the forbidden band width of each material is not the same, so release the photon wavelengths are also different, so the color of the LED is decided by the use of basic materials.
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