pn junction
(PN junction)
In single crystal semiconductors, when one part is doped with acceptor impurities and the other part is doped with donor impurities, P-type semiconductors and N-type semi-semiconductors.
The transition zone near the conductor interface is called. There are two kinds of PN junction: homogeneous junction and heterojunction. PN junction made of the same semiconductor material is called homogeneous junction, which is composed of band gaps with different widths.
A PN junction made of the same two semiconductor materials is called a heterojunction. The methods of manufacturing PN junction include alloying, diffusion, ion implantation and epitaxial growth. Manufacturing heterogeneity
The junction usually adopts epitaxial growth method.
There are many positively charged holes and negatively charged ionized impurities in P-type semiconductors. Under the action of electric field, holes can move, while ionized impurities (ions) are fixed. There are many movable negative electrons and fixed positive ions in N-type semiconductors. When the P-type and N-type semiconductors are in contact, holes diffuse from the P-type semiconductor to the N-type semiconductor and electrons diffuse from the N-type semiconductor to the P-type semiconductor near the interface. Holes and electrons meet and recombine, and carriers disappear. Therefore, there is a lack of carriers in the junction region near the interface, but there are charged fixed ions distributed in space, which is called space charge region. The space charge on one side of P-type semiconductor is negative ion, and the space charge on one side of N-type semiconductor is positive ion. The positive and negative ions generate an electric field near the interface, which prevents the carriers from spreading further and achieves equilibrium.
If a voltage is applied to the PN junction, if the P type is connected to the positive electrode and the N type is connected to the negative electrode, the current will flow from the P type to the N type, and holes and electrons will be bound.
The surface movement makes the space charge region narrow or even disappear, and the current can pass smoothly. If the N-type is connected to the positive electrode of the applied voltage and the P-type is connected to the negative electrode, the total number of holes is
The electrons move away from the interface, which widens the space charge region and prevents the current from flowing. This is the unidirectional characteristic of PN junction.
When reverse voltage is applied to PN junction, the space charge region widens and the electric field in the region increases. When the reverse voltage increases to a certain extent, the reverse current will suddenly increase. Ruowai
If the circuit can't limit the current, the current will be so large that it will burn the PN junction. The voltage when the reverse current suddenly increases is called breakdown voltage. There are two basic breakdown mechanisms, namely tunneling effect.
Track breakdown and avalanche breakdown. When the reverse voltage is applied to the PN junction, the positive and negative charges in the space charge region form a capacitive device. Its capacitance varies with the applied voltage.
According to the different PN junction materials, doping distribution, geometric structure and bias conditions, crystal diodes with multiple functions can be manufactured by using their basic characteristics. Li Ru
Rectifier diode, detector diode and switching diode can be made by PN junction unidirectional conduction, and Zener diode and avalanche diode can be made by breakdown characteristics. use
Tunnel diode is made of tunnel effect of highly doped PN junction; Varactor diode is made by using the effect that junction capacitance changes with external voltage. The photoelectric effect of semiconductor is related to PN junction.
We can also make various photoelectric devices. For example, semiconductor laser diodes and semiconductor light emitting diodes can be manufactured by carrier injection and forward bias heterojunction recombination.
Tube; Photodetector can be made by modulating the reverse current of PN junction by optical radiation. Solar cells can be made by photoelectric effect. In addition, two
The interaction between PN junctions can produce many electronic functions such as amplification and oscillation. PN junction is the core of bipolar transistor and field effect transistor, which is the modern electricity
The foundation of sub-technology. Widely used in diodes.