Encyclopedia of electronic components: characteristics of Semiconductors

The conductivity of a semiconductor is worse than that of a conductor, but stronger than that of an insulator. In fact, semiconductors differ from conductors and insulators in not only the ability to conduct electricity, but also the unique properties of semiconductors.
1., in pure semiconductors, the proper incorporation of certain kinds of extremely tiny impurities can lead to an increase in the electrical conductivity of semiconductors millions of times - the most striking and prominent feature of semiconductors. Transistors, for example, are made of this characteristic.
2., when the ambient temperature rises a little, the conductivity of the semiconductor increases significantly; when the ambient temperature drops a little, the conductivity of the semiconductor drops significantly. This property is called "thermal", and thermistors are made of this characteristic of semiconductors.
3 when there is a light on some of the semiconductor, the semiconductor like conductor, conductive ability is very strong; when there is no light, like these as conductive semiconductor insulator, this characteristic is called "light". For example, for the automatic control of "photodiode", "photoelectric transistor" and "photosensitive resistance" and so on, that is, the photosensitive characteristics of the semiconductor made.
As a result, temperature and illumination have a great impact on transistors. As a result, transistors cannot be placed in high temperatures and intense illumination. A black coat of paint on the surface of the transistor is also intended to prevent the light from affecting it. Finally, a fundamental test is made: the so-called semiconductor material is a material of crystalline structure, so the semiconductor is also called "crystal"".
P semiconductors and type N semiconductors - - previously described, adding a certain amount of trace impurities to a pure semiconductor can increase the electrical conductivity of semiconductors by a factor of a million. Join the impurity semiconductor can be divided into two types: one is added to the impurity in semiconductor to, in a semiconductor will produce a large number of negatively charged free electrons, such a semiconductor called "N type semiconductor" (also called "electronic semiconductor"); another impurities added to a semiconductor, will to produce a large number of positively charged "hole", such a semiconductor called "P type semiconductor" (also called "p-type semiconductor"). For example, in pure semiconductor germanium, a trace amount of impurity antimony is added to form a N type semiconductor. Similarly, if a small amount of impurities are added to the purified germanium, indium will form a P type semiconductor.
A PN structure, a crystal diode, tries to combine a P type semiconductor (with a large number of positively charged holes) and a N type semiconductor (a large number of negatively charged free electrons).
Where P type semiconductor type N semiconductor is combined, a special thin layer is formed. This particular layer is called "PN junction"". The crystal diode is actually made up of a PN structure.
For example, the application of the crystal diode radio, the Tentacula (i.e. stylus) part is equivalent to the P type semiconductor, N type germanium film is N type semiconductor, the contact surface between them is a p-n junction. The P terminal (or the P terminal) is called the positive end of the crystal diode (also called the positive electrode). The N terminal (or the N terminal leads) is called the negative end of the crystal diode (also called negative pole).
The positive end is connected to the positive electrode of the battery, and the negative end is connected to the negative electrode of the battery, which is the resistance value of the PN junction to a few hundred ohms. Therefore, the current through the PN junction (I=U/R) is very large. Such a connection method (Figure 2a) is called a forward connection". Positive connection, transistor diode (or PN) voltage withstand called forward voltage; in forward voltage, diode (or PN) resistance is called "positive resistance" in forward voltage, through the diode (or PN junction) current called forward current". Obviously, because of the positive resistance crystal diode is very small (a few hundred ohms), the forward voltage, forward current (I=U/R) will be great -- this shows that the forward voltage, diode (or PN) has the same ability as conductive conductor.
Conversely, if the P terminal is connected to the negative electrode of the battery, the N terminal is connected to the positive electrode of the battery (see Figure 2B). When the PN junction high resistance (up to hundreds beaten), current (I=U/R) hardly through the diode, or through the current is very weak. Such a connection method is called "reverse connection"". Reverse connection, transistor diode (or PN) voltage withstand called reverse voltage; in reverse voltage, diode (or PN) resistance is called "reverse resistance", in the reverse voltage, the diode (or PN junction) current is called "reverse current". Obviously, because the crystal diode forward high resistance (several hundred ohms), the reverse voltage under the forward current (I=U/R) will be very small, even negligible, which indicates that the reverse voltage of the diode (or PN junction), hardly conductive.
The experiments show that the crystal diode (or PN junction) has unidirectional conductivity.
The crystal diode is represented by the letter "D", which is commonly used in the circuit as a symbol for Figure 3, which means that the current (positive charge) flows only along the arrow, not the arrow. The
The use of one-way conductivity diode rectifier can be used (AC into DC) and receiver (remove the audio signal from high frequency or intermediate frequency signal) and frequency (such as the high frequency into 465 thousand weeks fixed).
The junction capacitance between PN junction ----PN and N type two fast semiconductors form a capacitance with very little capacitance, called "P" capacitance". As the resistance increases with frequency