Lighting principle:

          To understand the light-emitting principle of LED diodes, we must first understand the basic knowledge of semiconductors. The conductive properties of semiconductor materials are between those of conductors and insulator materials. Its uniqueness is that when the semiconductor is stimulated by external light and thermal conditions, its conductivity will change significantly; adding trace amounts to pure semiconductors impurity, its conductivity will also increase significantly. The most used semiconductors in modern electronics are silicon (Si) and germanium (Ge). Their outermost electrons are 4. When silicon or germanium atoms form a crystal, adjacent atoms interact with each other, making the outer electrons It becomes shared by two atoms, which forms the covalent bond structure in the crystal, which is a molecular structure with little confinement ability. At room temperature (300K), due to thermal excitation, some outermost electrons will gain enough energy to break away from covalent bonds and become free electrons. This process is called intrinsic excitation. After the electrons are freed from bondage and become free electrons, a vacancy will be left in the covalent bond. This vacancy is called a hole. The appearance of a hole is an important feature that distinguishes a semiconductor from a conductor. LED light 2.jpg

A small amount of pentavalent element impurities such as phosphorus is added to the intrinsic semiconductor. After it forms a covalent bond with other semiconductor atoms, there will be an extra electron. This extra electron only needs a very small amount of energy to get rid of the bond and become Free electrons, such impurity semiconductors are called electron semiconductors (N-type semiconductors). However, adding a small amount of trivalent element impurities (such as boron, etc.) to the intrinsic semiconductor, because it has only three electrons in the outer layer, will generate a vacancy in the crystal after forming a covalent bond with the surrounding semiconductor atoms. Semiconductors are called hole semiconductors (P-type semiconductors). After the combination of N-type and P-type semiconductors, there will be a difference in the concentration of free electrons and holes at their junction, so both electrons and holes will diffuse to the low concentration, leaving some charged but immobile ions, thereby destroying the original electrical neutrality of the N and P regions. These immobile charged particles are often called space charges, and they concentrate near the interface of the N and P regions to form a thin space charge region, which is what we call a PN junction.

After a forward bias voltage is applied to both ends of the PN junction (positive voltage is applied to the P-type side), the holes and free electrons will move with each other to form an internal electric field. The newly injected holes and free electrons then recombine, sometimes releasing excess energy in the form of photons while recombining, which is what we see as the light emitted by LEDs. Such a spectral range is relatively narrow. Since the forbidden band width of each material is different, the wavelength of the emitted photons is also different, so the color of the LED light is determined by the basic material used.