Jior: We know, diodes and transistors and resistors, coils and capacitors, different, having a rectification and amplification. In the structure of these semiconductor devices are used in a pn junction, pn junction why you need it?
Jior : PN junction is in the production of silicon crystals, the incorporation of a trivalent atoms (such as boron) or pentavalent atoms (e.g., arsenic), wherein a portion of the p-type semiconductor region, while the rest of the n-type semiconductor region is formed. This state of p-type region and n-type regions are connected together is called the pn junction. As for why the need to adopt a pn junction, let us follow the following ideas to consider it!
Jior: About the pn junction, there is a problem I would like to confirm. Is not to say, incorporation of the n-type semiconductor pentavalent atoms in the
body, the number of free electrons having negative charges should be greater than the number of positively charged holes. Similarly, in the p-type semiconductor, the number of holes should be more than the number of free electrons. In this way, it makes the n-type region will negatively charged as a whole, while the p-type region as a whole is positively charged it?
DOC : Oh, please stop for the moment to be left to its charged state based on the relative number of free electrons and holes!. In fact, from the point of view of charge .p-type region and the n-type region are neutral. When incorporation pentavalent or trivalent element present in the intrinsic semiconductor indeed many problems free electrons and holes will occur (and therefore also made of p-type and n-type semiconductor break). However, because if the crystal after incorporation in the silicon crystal is electrically neutral it is neutral trivalent element or pentavalent doping said positively, negatively charged completely wrong
Further, the contact surface of the p-type region and the n-type region, produces movement of free electrons and holes, so that the contact surface at both ends gathered from positive and negative charges (electric field is generated), it should be noted that due to of.
Mako: Why?
DOC : because from the perspective of charge transport, carrying free electrons and holes are charged, they are referred to as a carrier (carrier). Flow of current in the semiconductor due carrier movement is caused.
Think about it, to make the carrier mobility should be how to do it?
Jior: Since semiconductors free electrons and holes carry a charge, can it ...
By the way, if the electric field is applied · Empty along the electric field direction or the opposite direction under the influence of an electric field. This phenomenon is called drift current form it is called drift current. Think about it, in addition, are there any ways to make carrier movement it?
DOC: ? Oh, there it is a phenomenon known as diffusion phenomena, it is the birth of the phenomenon. This means that in the semiconductor, the direction of low concentration where the carrier is present when the difference in concentration high movement phenomenon.
So, as long as the electric field is a free electron or hole carriers will move from low concentration to high concentration direction where the phenomenon occurs in colorectal hair contact surface pn.
Imagine a person in the water droplets of ink, ink large expansion of the scope of the case will be open from small.
In conjunction with the surface of the pn junction, the concentration of free electrons and holes are definitely different. Therefore, free electrons and holes in the vicinity of the contact surface will be due to diffusion phenomena into each other's areas.
This result of diffusion in the region of the contact surface of the p-type side, holes are moved by the n-type region is formed of a negative charge region; n-type region contacting a side surface, free electrons are moved by the p-type region region to form a positive charge.
Jior: if the carrier is always such a move not only in the contact surface, then, p region and the n-type region is not completely reversed yet?
Dec: This fall do not worry. Because the contact surface is formed of positive and negative charges can result in an electric field, the electric field will disturb the movement of the surface of electrons and holes, will eventually maintain a balance. An electric field is referred to as a part of the depletion layer.
Thus, part of the depletion layer is generated a potential difference, the potential difference will prevent movement of carriers. This potential difference is called a potential barrier.
Now I understand why pn layer will produce a potential barrier junction depletion problem.
However, this diode or transistor to ~ in the end what use is it?
Doc: Well, do not worry, we must say the key point. In order to form a pn junction semiconductor
body current flows, carriers need to overcome a potential barrier of energy. That is, the carrier to be provided by an external across
this part of the potential energy difference. The reason for using a pn junction in a semiconductor device, is prepared in advance since such a potential barrier to control the number of carriers over the potential barrier by the application of this energy. In other words .pn junction it is precisely because of this potential barrier able to achieve control of the currents.
Mirko I would like to invite you to specifically explain
Dac. Pn junction, when a positive voltage is applied to the p region from the outside. Negative voltage is applied to the n-region, the depletion layer width will be narrowed That potential barrier lowering the carrier's activities will become active. That is, by applying a voltage can be made through the contact hole into the surface region from the p-n area, free electrons move from the n region to the p region. External voltage referred to as forward voltage, the current thus generated is referred to as a forward current.
External voltage is applied until the p region and n region is negative (this voltage is called a reverse voltage). · At this time since the width of the depletion layer increases, a potential barrier increases the number of carriers movable extremely small, so that a current (reverse current) by only insignificant.
It is because the potential barrier of the pn junction formed by the above reaction applied voltage, so that the pn junction can be used to achieve control of the currents. Also stop so as diodes and transistors in the electronic circuit as a current control action are very natural use of the pn junction.
Jior : diode structure itself is essentially a pn junction.
D0c: . Pn junction of the p and n region, respectively, together with the electrode leads, it is made of junction diodes. Of course, in addition to the junction diode, there are other types of diodes. Now, we take a look at some of the important characteristics of the diode bar.
Mako : voltage and current relationship is not linear junction diode. Whether Ohm's law also applies ah?
I understand that, in addition to the diode! Rectified available characteristics, can also be made of a Zener diode and a varactor diode used as a voltage regulator device. In addition, the laser diode may also be made into an optical communication device as a light source to transmit large amounts of information.
Capacitance diode is used as a voltage regulator device. In addition, the laser diode may also be made into an optical communication device as a light source to transmit large amounts of information.
. DOC diode has some important properties of: having only allows forward current through a rectifying property. The relationship between current and voltage, Ohm's law does not apply. This is because the resistivity of the semiconductor by an external temperature of greater impact sake. Only a small forward voltage is applied to a large current will flow through. The reverse voltage is increased to a certain value, it will produce a large reverse current rapidly increases. This reverse electronic music called Zener voltage (also known as the breakdown voltage). This phenomenon does not indicate the diode is damaged, when the voltage is reduced, the diode is still normal.
