Application of Semiconductors in the Aerospace Industry

1. Semiconductors Made into Photoresistors As discussed in the second issue, the conductivity of semiconductors depends not only on internal factors (internal structure, such as band gap width) but also on external factors (such as stimulation by light, heat, and electricity). Some semiconductor materials experience a particularly significant change in conductivity when irradiated by light, with their resistance decreasing drastically (generally by tens of thousands to hundreds of thousands of times). This effect is called the internal photoelectric effect. Components made using this effect of semiconductors are called photoresistors (Figure 1), which are generally made into thin layers with an area of about one square centimeter. Due to the different band gap widths of different semiconductor materials, the required activation energy varies, so their sensitivity to light of different wavelengths also differs. Some materials are very sensitive to visible light, some are particularly sensitive to infrared light, and others are most sensitive to X-rays, γ-rays, cosmic rays, etc. Photoresistors sensitive to visible light are now widely used in automatic control systems, whose schematic diagram is shown in Figure 2. In use, the photoresistor is connected in series with a power supply and an additional resistor, and then connected to the automatic control circuit. When there is no light irradiation, the resistance of the component is very large, so the current in the circuit is small. When irradiated by light, the resistance of the component decreases greatly, and the current in the circuit increases. This current is then used to start other circuits, or first passed through an amplification system before being connected to the automatic control circuit. This converts changes in light into changes in electricity, thereby achieving the purpose of light-controlled circuits. Since any incandescent object emits infrared light, photoresistors sensitive to infrared light can be used to detect hot objects at a considerable distance. For example, they can be used as the "eyes" of missiles to detect enemy aircraft several miles away, and then eliminate the enemy aircraft through a series of automatic control mechanisms. Such photoresistors are used for communication in the military, which can avoid the interference and interception of radio waves. In addition, we know that the universe is infinite, and cosmic rays radiate between stars. It is not difficult for us to make semiconductor photoresistors sensitive to these rays, which can be used as the eyes of interstellar rockets to explore and reveal the mysteries of the universe. 2. Semiconductors Made into Photoelectronic Tubes If the energy of photons incident on a semiconductor is sufficient, they can not only activate electrons in the semiconductor but also enable them to break free from various binding forces and escape from the semiconductor surface. The electrical change generated by this light change is called the external photoelectric effect because it makes electrons escape from the semiconductor. Components made using this effect are called photoelectronic tubes. Such components are also widely used in automatic control systems. 3. Semiconductors Made into Thermistors In addition to converting changes in light into electrical changes to make photoresistors, some semiconductor materials can convert changes in temperature into electrical changes to make thermistors, based on a principle similar to that of photoresistors. An increase in external temperature causes an increase in carriers inside the semiconductor, thereby increasing conductivity and decreasing resistance. Therefore, thermistors are made using the sensitivity of resistance to decrease (or increase) with increasing temperature. The sensitivity of semiconductor resistance to temperature is much higher than that of metals, which is why semiconductor thermistors are widely used in automatic control systems. Commonly used thermistors can be made into sheet, rod, bead, and filament shapes. These components are generally small in size and light in weight. For example, the diameter of a bead thermistor can be as small as 0.1 millimeters, and a rod thermistor is only as thin as a matchstick, with a weight of no more than a few tenths of a gram. This unique advantage meets the requirements of aerospace applications. For example, thermistors can be used to control the temperature of cylinder walls in aircraft. The circuits used for thermistors in automatic control systems are generally bridge circuits. In addition, thermistors are also widely used in aerospace measurement instruments. (III) Application of Semiconductors in Energy Conversion (Semiconductors Made into Small Generators) 1. Semiconductors Made into Solar Cells When semiconductor materials are irradiated by light, they can generate electromotive force. This effect is called the photovoltaic effect (Figure 3). Semiconductor components made using this effect are called solar cells, as they directly convert light energy into electrical energy. If connected with an external circuit, there will be current flowing in the circuit. Solar cells are generally made into circular thin film layers, with the area determined by needs. Since different materials have different band gap widths, we can manufacture solar cells of various materials according to the photon energy of various rays in the universe to meet the needs of small power generation equipment on interstellar vehicles. Many solar cells were used in the three Soviet artificial satellites. Obviously, solar cells can also be used in automatic control systems or measurement instruments. Their advantage over photoresistors is that they are generators themselves and do not require an additional power supply; the disadvantage is that they are more difficult to manufacture. The principle is very simple: it uses the energy radiated by radioactive elements to activate carriers inside the semiconductor to generate electromotive force. At present, atomic energy cells have not been widely used due to insufficient stability and unsatisfactory efficiency. However, it is certain that atomic energy cells have unlimited development prospects because they can directly convert atomic energy into electrical energy. Currently, atomic energy power stations convert atomic energy into electrical energy through repeated transformations, which obviously results in very low efficiency. Therefore, we can assert that this field of work has immeasurable development prospects. Our era has entered the atomic energy age, and aircraft will use atomic energy as power. Therefore, if a part around the atomic fuel is surrounded by appropriate semiconductor materials, wouldn't it become an atomic energy cell? Of course, this is still an ideal to be realized at present. (IV) Others Almost all of the three application aspects mentioned above have been realized. In fact, there can be inverse effects in each of the above effects. Solar cells are devices that convert light energy into electrical energy; conversely, special semiconductor materials can be used to convert electrical energy into light energy, that is, to make semiconductor lighting equipment. Similarly, thermoelectric cells use temperature differences to generate electricity; on the contrary, some semiconductor materials can be used to generate temperature differences using electrical energy, that is, to make one end of the semiconductor cool and the other end hot. The cold end can be used to make a semiconductor cooler, or semiconductor refrigerator. Currently, the semiconductor refrigerator made in the Soviet Union can reach minus 70℃. These devices can be used to cool some heat-sensitive components in aircraft, or to make protective boxes, insulated cabins, and so on. In addition, many materials are semiconductor materials. For example, ferrite magnets are used in the memory of aircraft computing systems, which are also semiconductor materials. In short, semiconductors have numerous uses in the aerospace industry, too many to list here. This is only a superficial general introduction. With the rapid development of the motherland's aerospace industry and the imminent realization of interstellar navigation, the application of semiconductors in aerospace will become increasingly widespread. Undoubtedly, semiconductors will better serve the motherland's socialist construction cause. The article and images are sourced from the internet. Please notify us for deletion if there is any infringement. Thank you.