Semiconductor main features

Semiconductor five characteristics: doping, thermal sensitivity, photosensitivity, negative resistivity temperature characteristics, rectification characteristics.

In a semiconductor forming a crystal structure, the electrical conductivity can be controlled by artificially adding specific impurity elements.

Under the conditions of light and thermal radiation, its conductivity has a significant change, in line diode.

Lattice: Atoms in a crystal form a neatly arranged lattice in space, called a lattice.

Covalent bond structure: a pair of outermost electrons (that is, valence electrons) of two adjacent atoms not only move around their own atomic nuclei, but also appear in the orbit of adjacent atoms, becoming a shared electron, forming a covalent bond.

Free electron formation: At room temperature, a small number of valence electrons obtain enough energy due to thermal motion to break free of the covalent bond and become free electrons.

Hole: The valence electron breaks free from the bond and becomes a free electron, leaving an empty position called a hole.

Electron current: Under the action of applied electric field, free electrons produce directional movement, forming electronic current.

Hole current: valence electrons fill holes in a certain direction in turn (that is, holes also produce directional movement), forming a hole current.

The current of an intrinsic semiconductor: electron current + hole current. Free electrons and holes carry charges of different polarity, and they move in opposite directions.

Charge carrier: The particles that carry an electric charge are called charge carriers.

The characteristics of conductor electricity: conductor conduction has only one carrier, that is, free electron conduction.

Characteristics of intrinsic semiconductor electricity: Intrinsic semiconductors have two kinds of charge carriers, namely free electrons and holes are involved in conducting electricity.

Intrinsic excitation: The phenomenon of a semiconductor producing free electrons and holes under thermal excitation is called intrinsic excitation.

Composite: The free electron in the process of movement if the hole meets the hole will fill the hole, so that the two disappear at the same time, this phenomenon is called composite, direct-plug diode.

Dynamic equilibrium: At a certain temperature, the number of free electron and hole pairs generated by the intrinsic excitation is equal to the number of compound free electron and hole pairs, and the dynamic equilibrium is achieved.

The relationship between the concentration of charge carriers and temperature: the temperature is certain, the concentration of charge carriers in the intrinsic semiconductor is certain, and the concentration of free electrons and holes is equal. When the temperature increases, the thermal motion intensifies, the number of free electrons breaking free of covalent bond increases, the number of holes also increases (that is, the concentration of charge carriers increases), and the conductivity increases. When the temperature decreases, the carrier concentration decreases and the conductivity deteriorates.

Conclusion: The conductivity of intrinsic semiconductor is related to temperature. The sensitivity of semiconductor material properties to temperature can make thermal and photosensitive devices, which also causes the poor temperature stability of semiconductor devices.

Impurity semiconductor: By diffusion process, a small amount of suitable impurity elements in the intrinsic semiconductor can be obtained.

P-type semiconductor: A trivalent element (such as boron) is added to a pure silicon crystal to replace the silicon atoms in the lattice, forming a P-type semiconductor.

Most carriers: In P-type semiconductors, the concentration of holes is greater than the concentration of free electrons, which is called most carriers, referred to as many carriers.

Minority carriers: In P-type semiconductors, free electrons are minority carriers, referred to as minority carriers.

Acceptor atom: The vacancy in the impurity atom absorbs electrons and is called acceptor atom.

The conductive characteristics of P-type semiconductor: it conducts electricity by hole, and the more impurities are added, the higher the concentration of moles (holes), and the stronger the conductive property.

N-type semiconductor: A pentavalent element (such as phosphorus) is added to a pure silicon crystal to replace the silicon atoms in the lattice to form an N-type semiconductor.

Many electrons: In N-type semiconductors, many electrons are free electrons.

Minority: In N-type semiconductors, minority is a hole.

Donor atom: The impurity atom can provide electrons and is called donor atom.

The conductive properties of N-type semiconductors: the more impurities are added, the higher the concentration of polyons (free electrons), and the stronger the conductive properties.

Conclusion:

The concentration of polyons depends on the concentration of impurities.

The concentration of small sons depends on the temperature.

Formation of PN junction: P-type semiconductor and N-type semiconductor are made on the same silicon wafer, and PN junction is formed at their interface.

The formation process of PN junction: as shown in the figure, the P-type semiconductor and N-type semiconductor are made on the same silicon chip, and under the action of no external electric field and other excitation, the number of many sons participating in the diffusion movement is equal to the number of few sons participating in the drift movement, so as to achieve dynamic equilibrium and form PN junction.

Diffusion motion: A substance always moves from a place of high concentration to a place of low concentration, and this movement due to the difference in concentration is called diffusion motion.

Space charge region: the free electrons diffused into the P region are compounded with holes, and the holes diffused into the N region are compounded with free electrons, so the concentration of many moles near the interface decreases, the negative ion region appears in the P region, and the positive ion region appears in the N region, which is not able to move, called the space charge region.

Electric field formation: The space charge region forms an internal electric field.

When the space charge is widened, the internal electric field is enhanced, and its direction is from the N region to the P region, which prevents the diffusion movement.

Drift motion: under the action of electric field force, the movement of the carrier is called drift motion.

Potential difference: The space charge region has a certain width, forming a potential difference Uho, and the current is zero.

Depletion layer: The number of free electrons and holes in most of the space charge regions is very small, and the role of carriers is often ignored in the analysis of PN junctions, and only the charge in the ion region is considered, which is called depletion layer.

The characteristics of PN junction: it has unidirectional conductivity.