Crystal diode

The basic structure of a crystal diode is a P-type semiconductor and an N-type semiconductor combined to form a PN junction. At the interface of the PN junction, the holes in the P-type semiconductor and the electrons in the N-type semiconductor diffuse to each other to form a dipole layer with space charges. This dipole layer prevents the continued diffusion of holes and electrons and makes the PN junction reach an equilibrium state. When the P end of the PN junction (the side of the P-type semiconductor) is connected to the positive electrode of the power supply and the other end is connected to the negative electrode, holes and electrons flow to the dipole layer to make the dipole layer thinner, and the current rises quickly. If the direction of the power supply is reversed, the holes and electrons will flow away from the dipole layer to make the dipole layer thicker, and the current is limited to a small saturation value (called reverse saturation current). Therefore, the PN junction has unidirectional conductivity.

bipolar transistor

It is composed of two PN structures, one of which is called the launch junction and the other is called the collector junction. A thin layer of semiconductor material between the two junctions is called the base region. The two electrodes connected to one end of the emitter junction and one end of the collector junction are called emitter and collector respectively. The electrode connected to the base is called the base. In application, the emitter junction is in forward bias and the collector is in reverse bias. A large number of minority carriers are injected into the base region through the current of the emission junction. These minority carriers migrate to the collector junction by diffusion to form a collector current. Only a very small amount of minority carriers recombine in the base region. Form the base current. The ratio of the collector current to the base current is called the common emitter current amplification factor. In a common emitter circuit, a small change in the base current can control a large change in the collector current, which is the current amplification effect of a bipolar transistor. Bipolar transistors can be divided into two types, NPN type and PNP type.

field effect transistor

It relies on a thin layer of semiconductor to change its resistance (referred to as the field effect) under the influence of the lateral electric field, so that it has the function of amplifying the signal. Two electrodes connected to the two ends of this thin-layer semiconductor are called source and drain. The electrode that controls the lateral electric field is called a grid.

According to the structure of the gate, field effect transistors can be divided into three types:

① Junction FET (using PN structure to form grid);

② MOS field effect transistor (a gate is formed of metal-oxide-semiconductor, see metal-insulator-semiconductor system);

③ MES field effect tube (the gate is formed by contacting metal and semiconductor); among them, MOS field effect tube is the most widely used. Especially in the development of large-scale integrated circuits, MOS large-scale integrated circuits have special advantages. MES FETs are generally used in GaAs microwave transistors.

On the basis of MOS devices, a charge-coupled device (CCD) has been developed, which uses the stored charge near the surface of the semiconductor as information, and controls the potential well near the surface to transfer the charge in a certain direction near the surface. This device can usually be used as a delay line and memory, etc.; coupled with a photodiode array, it can be used as a camera tube.