A Diode Is Different From A Triode. Bring You A New Understanding of Diodes

A diode is different from a triode. Bring you a new understanding of diodes

The copyright belongs to the author. For commercial reprinting, please contact the author for authorization. For non-commercial reprinting, please indicate the source.

It was in the winter of 1947 that three scientists at Bell LABS invented the transistor, changing the world and driving the global semiconductor electronics industry. So 10 years later, another winter, the three brothers won the Nobel Prize in physics. However, this triode was not invented out of thin air, from a structural point of view, she is composed of two diodes, absolutely forced diode "dry son". Today brings you the legend of the "godfather" diode. 1 diode =PN junction + vest in the semiconductor performance was discovered, the diode became the world's first semiconductor device, the most common structure is, in the PN junction plus lead and package, it becomes a diode, it can even be said that the diode is actually made of a PN structure, so the working principle of the diode is about equal to the working principle of PN, Small series from the source to talk about the diode (PN junction) in the end how to come? 1.1 The good brother of the diode PN section: P-type semiconductor, N-type semiconductor We generally divide the object into conductors, insulators and semiconductors according to the different electrical conductivity (resistivity). More generally, a semiconductor that is completely pure and free of impurities is called an intrinsic semiconductor. The main common representative is silicon, germanium, these two elements of the single crystal structure. But the actual semiconductor can not be absolutely pure, this kind of semiconductor is called impurity semiconductor. P-type semiconductor If we add a little boron (the outermost layer has 3 electrons) to pure silicon, it will lose 1 electron, and form a hole, so that the formation of P-type semiconductor (less 1 negatively charged atom, can be seen as more than 1 positive charge). When the trivalent impurity atom forms a covalent bond with the silicon atom, it lacks a valence electron and leaves a hole in the covalent bond. In P-type semiconductors, holes are the majority of charge carriers, which are mainly formed by doping. Free electrons are a few charge carriers, formed by thermal excitation. The holes easily trap electrons, causing the impurity atoms to become negative ions. The trivalent impurity is therefore also called the acceptor impurity. N-type semiconductor If a little arsenic or phosphorus is doped in pure silicon (the outermost layer has 5 electrons), there will be one more free electron, so as to form an N-type semiconductor, because only four valence electrons in the pentavalent impurity atom can form covalent bonds with the valence electrons in the surrounding four semiconductor atoms, and the excess one valence electron is easily formed free electrons because there is no covalent bond bondage. As shown in the figure. <img Free electrons are the majority carriers in N-type semiconductors, which are mainly provided by impurity atoms; The holes are a few charge carriers, formed by thermal excitation. Pentavalent impurity atoms that provide free electrons become positive ions due to their positive charge, so pentavalent impurity atoms are also called donor impurities. 1.2 PN junction =P∩N(note: "∩" intersection) On a complete silicon chip, after using different doping processes to form an N-type semiconductor on one side and a P-type semiconductor on the other side, the area near the interface of the two semiconductors is a PN junction. In the space charge region, due to the lack of multiple particles, it is also known as the depletion layer. The <img >PN junction has electrons on each end, so that the current can only flow in one direction. When no voltage passes through the diode, electrons flow from the N-type semiconductor to the P-type semiconductor along the junction between the transition layers, creating a depletion zone. In the loss zone, the semiconductor material returns to its original insulating state - all these "electron holes" are filled, so there are no free electrons and no current flowing. 2 diode PN section unidirectional conductivity characteristics - the most important! 2.1 Diode small experiment In an electronic circuit, the positive electrode (P region) of the diode is connected to the high potential end, the negative electrode (N region) is connected to the low potential end, the diode will be switched on, this connection is called forward bias. It must be noted that when the forward voltage added to both ends of the diode is very small, the diode still cannot be switched on, and the forward current flowing through the diode is very weak. Only when the forward voltage reaches a certain value (this value is called the "threshold voltage", germanium tube is about 0.2V, silicon tube is about 0.6V), the diode can be directly positive conduction. After the diode is switched on, the voltage at both ends of the diode remains essentially unchanged (about 0.3V for the germanium tube and about 0.7V for the silicon tube), which is called the "forward voltage drop" of the diode. The positive electrode (P region) of the diode is connected to the low potential end, the negative electrode (N region) is connected to the high potential end, at this time there is almost no current flowing in the diode, at this time the diode is in a cut-off state, this connection is called reverse bias. When the diode is in reverse bias, there will still be a weak reverse current flowing through the diode, which is called leakage current. When the reverse voltage at both ends of the diode increases to a certain value, the reverse current will increase sharply, the diode will lose the single-direction conduction characteristics, at this time the diode is broken down, which is the reverse breakdown characteristics of the diode, which will be introduced in the next section. 2.2 The diode rises to the theory In order to remove the depletion region, it is necessary to make the N-type move to the P-type and the hole should move in the opposite direction. In order to achieve the purpose, the N pole of the PN junction is connected to the negative pole of the power supply, and the P pole is connected to the positive pole. The free electrons in the N-type semiconductor are repelled by the negative electrons and attracted to the positive electrons, while the electron holes in the P-type semiconductor move in the other direction. When the voltage between the electrons is high enough, the electron in the depletion region will begin to move freely in its electron hole again, the depletion region will disappear, and current will flow through the diode. If the P pole is connected to the negative terminal of the power supply, the N type is connected to the positive terminal. The current will not flow. The negative electrons of an N-type semiconductor are attracted to the positive electrons. The positive electron hole of a P-type semiconductor is attracted to the negative electron. Because the electron holes and electrons are moving in the wrong direction, no current flows through the junction, the depletion region increases, and the V-I characteristic expression of the PN junction (the volt-ampere characteristic curve, IS -- reverse saturation current; VT - voltage equivalent of temperature; And at room temperature (T=300K)

3. When PN junction is applied with forward voltage, it has low resistance and large forward diffusion current. PN junction has high resistance and small reverse drift current when reverse voltage is applied. PN junction has unidirectional conductivity. 3 diode PN section reverse breakdown - greatly useful! When the reverse voltage of the PN junction increases to a certain value, the reverse current suddenly increases rapidly, which is called the reverse breakdown of the PN junction. When reverse breakdown occurs, the voltage at both ends of the PN junction is almost unchanged in the range of large reverse current changes, as shown in the figure. Reverse breakdown is divided into electrical breakdown and thermal breakdown, PN junction thermal breakdown after the current is very large, the voltage is very high, the power consumed on the junction is very large, easy to make PN junction heat, PN junction burned. Thermal breakdown is irreversible. PN junction electrical breakdown can be divided into avalanche breakdown and Zener breakdown from its causes.