Magazine Semiconductor: An impurity semiconductor can be obtained by incorporating a small amount of impurity elements into the intrinsic semiconductor by a diffusion process.
The N-type semiconductor and the P-type semiconductor can be formed according to the impurity element doped, and the conductivity of the impurity semiconductor can be controlled by controlling the concentration of the impurity element.
N-type semiconductor: An N-type semiconductor is formed by incorporating a valence element (such as phosphorus) into a pure silicon crystal to replace the position of the silicon atom in the crystal lattice.
Since the outermost layer of the impurity atom has five valence electrons, in addition to forming a covalent bond with the surrounding silicon atom, one more electron is added. The extra electrons are not bound by covalent bonds and become free electrons. In the N-type semiconductor, the concentration of free electrons is larger than the concentration of holes, so the free electrons are called majority carriers, and the holes are minority carriers. Since an impurity atom can provide electrons, it is called a donor atom. P-type semiconductor: A P-type semiconductor is formed by doping a trivalent element (such as boron) into a pure silicon crystal to replace the position of the silicon atom in the crystal lattice.
Since the outermost layer of the impurity atom has three valence electrons, when they form a covalent bond with the surrounding silicon atom, a "vacancy" is generated. When the outermost electron of the silicon atom fills the vacancy, its covalent bond A hole is created in it. Therefore, in the P-type semiconductor, the holes are multi-parts and the free electrons are minority. Since the vacancies in the impurity atoms absorb electrons, they are called acceptor atoms.
PN junction
PN junction: P-type semiconductors and N-type semiconductors are fabricated on the same silicon wafer using different doping processes, and a PN junction is formed at their interface.
Diffusion movement: The substance always moves from a place where the concentration is high to a low concentration, and the movement due to the difference in concentration becomes a diffusion movement. When a p-type semiconductor and an N-type semiconductor are fabricated together, at their interface, the concentration difference between the two carriers is large, and thus the holes in the P region are necessarily diffused toward the N region, and at the same time, the N region The free electrons also inevitably diffuse into the P region. Since the free electrons diffused into the P region coincide with the holes, and the holes diffused into the N region conform to the free electrons, the concentration of the multiple ions decreases near the interface, and negative ions appear in the P region. In the region, the positive ion region appears in the N region, and they are immovable, and become space charges to form a built-in electric field ε.
As the diffusion motion progresses, the space charge region is widened, and the built-in electric field is enhanced. The direction is from the N region to the P region, which just happens to organize the diffusion motion.
Drifting motion: Under the action of electric field force, the motion of carriers is called drifting motion.
When the space charge region is formed, under the action of the built-in electric field, the minority has a drifting motion, the holes move from the N region to the P region, and the free electrons move from the P region to the N region. Under nowhere electric field and other excitation, the number of multi-sub-parts participating in the diffusion motion is equal to the number of minority children participating in the drift motion, thus achieving dynamic balance and forming a PN junction. At this time, the space charge region has a certain width, and the potential difference is ε= Uho, the current is zero.