History & Applications of Semiconductors
Update Time: Feb 01, 2024 Readership: 49
Semiconductors are the basis of informatization. The invention of semiconductor large-scale integrated circuits, semiconductor lasers, and various semiconductor devices in the last century played a vital role in the modern information technology revolution and triggered a new global industrial revolution. Informatization is a major trend in economic and social development in the world today, and the level of informatization has become an important indicator of the modernization of a country and region. Entering the 21st century, the world is accelerating the pace of informatization construction.
History of Semiconductors
Due to the needs of the information technology revolution, semiconductor physics, materials, and devices will have new and faster developments. The size of integrated circuits will become smaller and smaller, and new quantum effect devices will appear; wide bandgap semiconductors represent a new direction and will have broad applications in short-wavelength lasers, white light emitting tubes, high-frequency high-power devices, etc. ; Nanoelectronic devices may serve as the next generation of semiconductor microelectronics and optoelectronic devices; the use of single electrons, single photons and spin devices as quantum control will play a key role in the practical application of quantum computing and quantum communications.
At the end of World War II in 1945, Barclay, the president of Bell Labs in the United States, decided to establish a solid-state physics group in order to adapt to the laboratory's transition from wartime to peacetime work needs. Shockley was in charge of the semiconductor physics group, with members including Bardeen, Bratton, Gibney, Moore, et al. Shockley and Bardeen were theoretical physicists, Bratton was an experimental physicist, Gibney was a physical chemist, and Moore was a circuit scientist. This combination of professional talents was crucial to semiconductor physics research and the invention of the transistor.
It is a golden combination, capable and efficient. Based on their respective experiences and subsequent considerations after the mid-1930s, they focused on the research of semiconductor materials silicon and germanium from the very beginning. During World War II, Britain used radar to detect German bombers. The core of radar is a vacuum tube, which can amplify weak currents. As early as 1939, Shockley was preparing to create solid-state devices that could amplify current to replace vacuum tubes. In December 1947, Bardeen and Brattain made the world's first germanium point contact transistor, which had a current amplification function.
Bardeen and Brattain results were published in June 1948. Although the invention of the point-contact transistor opened the prelude to the great development of transistors, due to its complex structure, poor performance, large size, and difficulty in manufacturing, it has not been promoted and applied in the industry, and the response in society has not been strong enough. In January 1948, Shockley invented another surface junction transistor based on his own research on p-n junction theory, and obtained a patent in June 1948. Surface junction transistors, also known as field effect transistors, are planar (see Figure 3) and can be mass-produced through some planar processes (such as diffusion, mask, etc.). Therefore, it was only after the invention of the surface junction transistor that the advantages of the transistor were well understood and it gradually replaced the vacuum electron tube.
Bardeen, Bratton, and Shockley received the Nobel Prize in Physics in 1956 for their contributions to the invention of the transistor and the junction transistor. The first application of semiconductor transistors was Sony's portable radio, which became popular all over the world and made a lot of money. 3. The Invention of Integrated Circuits Transistor radios are much smaller than tube radios and can be carried anywhere. But it is made up of transistors, resistors, capacitors, and magnetic antennas welded on a circuit board, and connected to each other by wires. The volume is relatively large and the assembly process is complicated.
In 1958, the U.S. government established the Transistor Circuit Miniaturization Fund to meet the needs of the United States in catching up with the first artificial satellite launched by the former Soviet Union. At that time, Kilby of Texas Company took on the task of trying to create miniaturized circuits that packaged transistors, resistors, capacitors, etc. together. In September 1958, Kilby made the world's first integrated circuit oscillator, all of which was recorded in his notes of that day. The integrated circuit invented by Kilby was patented in February 1959, and was named "Miniaturized Electronic Circuit". At the same time, Noyce of Fairchild Semiconductor in California came up with the idea of using aluminum to connect transistors. Five months after Kilby invented the integrated circuit, in February 1959, he used the planar transistor method proposed by Horney to generate a SiO2 mask on the entire silicon wafer, and used photolithography technology to carve windows and leads according to the template. The vias diffuse impurities through the windows to form the base, emitter and collector, and the gold or aluminum is evaporated to create an integrated circuit.
In July 1959, Noyce obtained a patent for his integrated circuit, titled "Semiconductor Device and Lead Structure." Since then, integrated circuits have entered a new era of large-scale development. 4. The invention of solar cells In order to meet the needs of artificial satellites, Pearson and Fuller used the diffusion technology of phosphorus and boron to create a large-area silicon p-n junction solar cell in 1954. The photoelectric conversion efficiency reached more than 6%, exceeding the best in the past. 15 times the solar energy conversion efficiency. It was cheap to make and could be mass-produced, so it quickly became widely used. Solar cells work on the photovoltaic effect. When light shines on a semiconductor, electron-hole pairs are generated in the semiconductor. If an external circuit is connected, current will flow through it, which is the photovoltaic effect. Commercial applications of solar cells began in 1958, when they were selected as the power source for the radio transmitter of Vanguard I, the first U.S. satellite. Under the current energy crisis, solar cells have attracted great attention as a renewable and non-polluting power source.
The invention of the semiconductor laser
The working principle of semiconductor light-emitting tubes and lasers is exactly the opposite of that of solar cells: solar cells use light to generate electricity, while light-emitting tubes and lasers use electricity to generate light. Electric current is used to introduce electrons and holes into the conduction band and valence band of the semiconductor, respectively. Electrons and holes recombine to produce photons. In 1962, Hall in the United States made the first semiconductor laser using a p-n homojunction. Three conditions must be met to generate laser light: an inverted distribution of particle numbers, a resonant cavity, and a current exceeding a certain threshold. In 1963, Kramer of the United States and Alferov of the Soviet Union independently made heterojunction lasers. In Figure 8, the junction area uses a material with a small bandgap, such as GaAs; the p on both sides The area and n-region use another material with a large band gap, such as AlxGa1-xAs. In this way, the luminescent area is limited to the narrow nodule area. Therefore, the luminous efficiency is greatly improved and the threshold current of the laser is reduced. In 1970, the Soviet Union's Yoffei Research Institute and the United States' Bell Labs respectively produced double heterojunction lasers that worked continuously at room temperature, thus making semiconductor lasers widely used in optical communications. Due to their important contributions to the development of semiconductor lasers, Kromer and Alferov won the Nobel Prize in Physics together with Kilby, the inventor of the integrated circuit, in 2000. The invention of silicon large-scale integrated circuits and semiconductor lasers has brought the world into an information age based on microelectronics and optoelectronics technology, which has greatly promoted social and economic development.
The invention of molecular beam epitaxy
A key technology for manufacturing double heterojunction lasers is molecular beam epitaxy. In 1968, Zhuo Yihe of Bell Labs discovered that by precisely controlling the size and time of the beam in an ultra-high vacuum container, different layers and types of semiconductor materials could be grown as needed, thus inventing molecular beam epitaxy. The schematic diagram of the molecular beam epitaxy equipment is shown in Figure 11. The inside of the device is under ultra-high vacuum conditions (10-10torr), and the evaporation furnace is equipped with sources of raw material elements (such as Ga, As, Al, etc.). The front is a controllable baffle. When the baffle is opened, the evaporated source atoms are directly directed onto the heated substrate for epitaxial growth. At present, this technology can already achieve the growth of single atomic layers. Surrounding the device are some detection instruments to monitor the growth process.
Applications of Semiconductor Technology
Large-scale integrated circuits and computers Large-scale integrated circuits have laid the foundation for the development of computers and networks. According to Moore's Law, the integration level of integrated circuits is doubling every 18 months. Recently, its thickness has reached tens of nanometers (millimeters, micrometers, nanometers), and each chip contains tens of billions of components. . Computer science has developed to a very high level. Both computer hardware and software are very mature. Computers with trillions of operations per second or even higher (Tianhe: 2000 trillion operations, second in the world) have been developed. This is Various high-speed operations, massive information processing and conversion provide powerful tools.
Since the birth of computers in 1943, due to the invention of integrated circuits, computers have rapidly developed towards high computing speed and miniaturization. At present, the world's major developed countries and China already have large computers with more than one quadrillion floating-point operations. China ranks second in the world in manufacturing and owning such supercomputers, after the United States. This kind of supercomputer can be used to analyze proteins, develop new drugs, etc., and can be used in the military to simulate nuclear explosions, decipher codes, etc. It should be noted that China is still very backward in the large-scale integrated circuits required to manufacture such computers, and most of them still need to be imported.
In the past, long-distance communication relied on long-distance telephone calls or telegraphs. Because the number of calls is small, the price is very expensive. In 1966, K. C. Kao of the British Standards Communications Laboratory proposed using impurity-free and highly transparent glass fibers to transmit laser signals. If its loss can be as low as 20 dB/km, long-distance optical communication can be achieved