When a voltage is applied across a semiconductor, the valence electrons superimpose the directional motion caused by the electric field on the basis of the irregular thermal motion, forming a current, and its motion state also changes, so its kinetic energy It must be different from the original heat movement. In the crystal, according to the Pauli exclusion principle, each energy level can accommodate up to two electrons. Therefore, to change the state of motion of electrons in the crystal in order to change the energy of the electrons and make it transition to a new energy level, it is generally necessary to satisfy two conditions: one is to have an external effect that can provide energy to the electrons; The level at which electrons are to jump is empty. Since there are a large number of empty energy levels in the conduction band, when the electric field SRM2A256SL-TM70 acts, the conduction band electrons can get energy and transition to the empty energy level, that is, the conduction band electrons can change the motion state. That is to say, under the action of the electric field, the conduction band electrons can generate directional motion to form a current, so the conduction band electrons can be electrically conductive. If the valence band is filled with electrons and there is no empty energy level, under the action of the applied electric field, the electrons do not have enough energy to excite the conduction band. Then, the state of the electron motion cannot be changed, and thus the directional motion cannot be formed, and there is no current. Therefore, the electrons in the valence band filled with electrons are not electrically conductive. If some of the electrons in the valence band transition to the conduction band under the influence of the outside world, then there is a lack of electron vacancies in the valence band. It is conceivable that under the action of an applied electric field, electrons of adjacent energy levels can leap into these vacancies, and new vacancies appear in the original energy levels of these electrons. In the future, other electrons can jump into these new vacancies again, just as if the vacancies move in the valence band, but the direction of movement is opposite to that of electrons. Therefore, for a valence band with electronic vacancies, the state of electronic motion is no longer immutable. Under the action of an applied electric field, some electrons superimpose the directional motion on the original thermal motion, thereby forming a current. The conduction between the conduction band and the valence band electrons is different, that is, the more electrons in the conduction band, the stronger the conductivity; and the more vacancies in the valence band, the less electrons, the stronger the conductivity. Imagine the electronic vacancies in the valence band as positively charged particles. Obviously, it carries the same amount of electricity as the electrons, with the opposite sign. Under the action of an electric field, it can move freely in the crystal, and it can conduct electricity like electrons in the conduction band. The electron vacancies in this valence band are usually called holes. Nangan Yu. Both the child and the rate can be electrically conductive. Generally speaking, the officials are collectively referred to as carriers. The semiconductors that are pure and structurally intact are called intrinsic semiconductors. It is assumed that the intrinsic semiconductor energy band diagram is resistant to light, electricity, magnetism, etc. in absolute zero resistance. At this time, the conduction band has no electrons, and the valence band has no holes. Therefore, the intrinsic semiconductor at this time is not electrically conductive like the insulator. However, since the forbidden band width Eg of the semiconductor is small, the electrons of the valence band can excite the transition to the conduction band under the action of thermal motion or other external factors. At this time, the conduction has electrons, the valence band also has holes, and the intrinsic semiconductor has electrical conductivity. The direct excitation of electrons by the valence band to the conduction band is called intrinsic excitation. For intrinsic semiconductors, their carriers can only be generated by intrinsic excitation. Therefore, the electrons of the conduction band and the holes of the valence band are equal, which is the characteristic of the conduction mechanism of the intrinsic semiconductor. In fact, crystals always contain defects and impurities, and many of the properties of semiconductors are determined by the impurities and defects that are incorporated. Impurities and defects have a decisive influence on the semiconductor, mainly due to the formation of bound electron states in the vicinity of impurities and defects, just as electrons are trapped near the nucleus in isolated atoms. Since the energy of the energy band corresponds to each energy level of the basic atom of the crystal (at least if the energy band is not very wide), and the energy level on the impurity atom is different from other atoms in the crystal, its position It may not be in the range of the crystal band. In other words, the energy level of the impurity can be in the forbidden band of the crystal level, that is, the energy of the bound state is generally in the forbidden band. In silicon crystals, silicon has four valence electrons, and atoms of group V elements (such as phosphorus, arsenic, antimony, etc.) replace the positions of silicon atoms. Among the five valence electrons of the group V, four valence electrons form a covalent bond with the silicon atom, and the excess one valence electron is not in the valence bond, and thus the free electron participates in the conduction. Electrons that are capable of conducting electricity are generally electrons in the conduction band. Therefore, the incorporation of a group V impurity in silicon can release an electron to the conduction band of the silicon crystal, and the impurity itself becomes a positive electric center. An impurity having such a characteristic is called a donor impurity because it can give electrons; in an ionic crystal, a positive ion or a negative ion in a gap is absent, and is actually a positive electric center, so it is also a donor. The energy state of the electrons bound to the donor is called the donor level. In a silicon crystal, when four covalent bonds are formed by substituting silicon atoms with atoms of a group III element having three valence electrons (such as boron, aluminum, marry, indium, etc.), there is still one electron missing, that is, there is an empty The state of electron energy, which accepts an electron from the valence band of the crystal, is equivalent to providing a vacancy to the valence band. Group III atoms are inherently neutral, and when they receive an electron, they become a negative center. An impurity having this characteristic is called an acceptor impurity because it can accept electrons. The acceptor's empty energy state is called the acceptor level. In ionic crystals, positive ion vacancies or interstitial negative ions also act as negative centers and are also acceptors. The process by which electrons (or holes) at the donor (or acceptor) level transition into the conduction band (or valence band) is called ionization. The energy required for this process is the ionization energy. The process by which holes are excited from the acceptor level to the valence band is actually the process by which electrons are excited from the valence band to the acceptor level. E1 indicates the bottom of the conduction band, and E+ indicates the top of the valence band. Generally, the donor level is closer to the bottom of the conduction band, that is, the bound state of the impurity is slightly lower than the bottom of the conduction band, so that the electrons in the conduction band are far away at the normal temperature due to the excitation of electrons in the bound state. More than the holes in the valence band. This semiconductor, which is mainly made of electrons, is called an N-type semiconductor. Generally, the acceptor level is closer to the top of the valence band, that is, when a certain impurity is incorporated into the semiconductor and its bound state is slightly higher than the valence band top, it can be excited at the normal temperature by the electrons in the valence band. Thus, the holes in the valence band are much more than the electrons in the conduction band. Such a semiconductor which is mainly made of a hole is called a P-type semiconductor. Since the ionization energy of the impurity is much smaller than the forbidden band width, the kind and amount of the impurity have a great influence on the conductivity of the semiconductor. In an N-type semiconductor, since n ≥ p, an electron is generally referred to as a majority carrier, and a hole is referred to as a minority carrier; in a P-type semiconductor, a hole is called a majority carrier , electrons are minority carriers. Oled Display Module,Segment Led Display Module,Module Pcb Oled Display,Oled Display Micro ESEN Optoelectronics Technology Co., Ltd, , https://www.esenlcd.com
