Introduction Semiconductor devices (semiconductor devices) usually use different semiconductor materials, adopt different processes and geometric structures, and have developed a wide variety of crystal diodes with different functions and uses. The frequency coverage range of crystal diodes can be

From low frequency, high frequency, microwave, millimeter wave, infrared to light wave.

Three-terminal devices are generally active devices, typically represented by various transistors (also known as crystal triodes).

Transistors can be divided into two categories: bipolar transistors and field-effect transistors.

According to different uses, transistors can be divided into power transistors, microwave transistors and low-noise transistors.

In addition to general transistors used for amplification, oscillation, and switching, there are also some special-purpose transistors, such as photoelectric crystals, magnetosensitive transistors, field effect sensors, etc.

These devices can not only convert information about some environmental factors into electrical signals, but also have the amplification effect of general transistors to obtain larger output signals.

In addition, there are some special devices, such as single-junction transistors that can be used to generate sawtooth waves, controllable silicon that can be used in various large-current control circuits, and charge-coupled devices that can be used as imaging devices or information storage devices.

In military equipment such as communications and radar, weak signals are mainly received by high-sensitivity, low-noise semiconductor receiving devices.

With the rapid development of microwave communication technology, microwave semiconductor low-noise devices have developed rapidly, the operating frequency continues to increase, and the noise coefficient continues to decrease.

Microwave semiconductor devices have been widely used in air defense and anti-missile, electronic warfare, C(U3)I and other systems due to their excellent performance, small size, light weight and low power consumption.

Classification 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, a dipole layer with space charge is formed because the holes in the P-type semiconductor and the electrons in the N-type semiconductor diffuse toward each other.

This dipole layer prevents the continued diffusion of holes and electrons and allows the PN junction to reach an equilibrium state.

When the P end of the PN junction (P-type semiconductor side) 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, making the dipole layer thinner, and the current rises quickly.

If the direction of the power supply is reversed, holes and electrons will flow away from the dipole layer, making the dipole layer thicker, and the current will be limited to a small saturation value (called reverse saturation current).

Therefore, the PN junction has unidirectional conductivity.

In addition, the dipole layer of the PN junction also acts as a capacitor, and this capacitance changes as the applied voltage changes.

The electric field is very strong inside the dipole layer.

When the applied reverse voltage reaches a certain threshold, avalanche breakdown will occur inside the dipole layer, causing the current to suddenly increase by several orders of magnitude.

Diodes made using these characteristics of PN junctions in various application fields include: rectifier diodes, detection diodes, frequency conversion diodes, varactor diodes, switching diodes, and voltage stabilizing diodes.

body (Zener diode), avalanche diode (collision avalanche transit diode) and trapping diode (trapped plasma avalanche transit time diode), etc.

In addition, there are tunnel diodes that utilize the special effects of PN junctions, as well as Schottky diodes and Gunn diodes without PN junctions.

Bipolar transistor is composed of two PN structures, one of which is called the emitter 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 region is called the base.

When applied, the emitter junction is forward biased and the collector is reverse biased.

The current passing through the emitter junction injects a large number of minority carriers into the base region. 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 and form a collector current.

Form base current.

The ratio of the collector current to the base current is called the ***emitter current amplification coefficient?.

In the ***emitter circuit, small changes in base current can control large changes in collector current. This is the current amplification effect of bipolar transistors.

Bipolar transistors can be divided into two types: NPN type and PNP type.

Field effect transistor relies on a thin layer of semiconductor to change its resistance under the influence of a lateral electric field (referred to as field effect), so that it has the function of amplifying signals.

The two ends of this thin layer of semiconductor are connected to two electrodes called source and drain.

The electrode that controls the lateral electric field is called a gate.

According to the structure of the gate, field effect transistors can be divided into three types: ① Junction field effect transistors (using a PN structure to form the gate); ② MOS field effect transistors (using metal-oxide-semiconductor to form the gate, see metal-insulator

-Semiconductor system); ③MES field effect transistor (using metal and semiconductor contact to form a gate); among them, MOS field effect transistor is the most widely used.

Especially in the development of large-scale integrated circuits, MOS large-scale integrated circuits have special advantages.

MES field effect transistors are generally used in GaAs microwave transistors.

On the basis of MOS devices, a charge-coupled device (CCD) has been developed, which uses the charge stored near the semiconductor surface as information and controls the potential well near the surface to transfer the charge in a certain direction near the surface.