The drift motion and diffusion motion in the PN junction are due to a concentration gradient. The majority of the electrons will diffuse in the direction of the minority, that is, the holes in the P region diffuse to the N region, leaving charged doped particles; the free electrons in the N region move to the P region. Diffusion, leaving behind positively charged dopant particles. The current generated by the carrier diffusion movement caused by the concentration gradient is [diffusion current] (only related to the concentration gradient).
The concept of PN junction
The P-type doped region and the N-type doped region form in contact, and there is a dynamic balance between the two.
Most of the electrons are holes, and the minority are free electrons.
Most electrons are free electrons, and the minority are holes.
After the diffusion movement, the harmful particles leave in the P region, and the positive particles leave in the N region. A built-in electric field will form between them. The direction is that the N region points to the P region. The free electrons in the region move to the N region, and the holes in the N region move to the P region. The current formed by the built-in electric field causing the drift movement of carriers calls “drift current.”
Dynamic balance of PN junction
Diffusion motion (producing diffusion current) will enhance the built-in electric field, thereby enhancing drift motion (producing drift current); drift current will make minority carriers drift toward the direction of multi-subs, thereby supplementing the multi-subs lost by diffusion motion, making the built-in The electric field weakens; finally, the diffusion motion and the drift motion reach a dynamic equilibrium.
The hole itself does not exist. It is formed by free electrons breaking free, so the built-in electric field, the Diffusion of many and few carriers, is the Diffusion of electrons from the boundary of the n-region to the boundary of the p-region. The boundary of the n-region presents a + property as a whole because of the lack of electrons. Moreover, the boundary of the p region presents a – property, thus forming an internal electric field, which cannot expand infinitely because its electric field makes it more and more difficult for electrons to move from the n region to the p region, in the process. The electrons in the boundary of the p region will return to the boundary of n region because of this electric field. Note that in the textbook. It says that the internal electric field causes the minority to move in the direction of the majority. This minority can be directly called electrons, including the p region itself. The minority electrons, including the multi-sub electrons diffused from the n region first,), then pull a bunch of them together, with the support of the internal electric field, so that the electrons can achieve dynamic back-and-forth equilibrium. The number of carriers in the drift motion is the same to achieve dynamic equilibrium). This statement is flawed. In essence, the diffusion electrons and the electric field electrons balance each other, and it is no longer the so-called balance between the many and the few.