The synthesis of the first generation of semiconductor materials, germanium, and its application in the AI era

As the first generation of semiconductor materials, germanium has high purity, high electron mobility, high hole mobility and good voltage stability. It is an ideal material for manufacturing transistors, integrated circuits and solar cells. It has extremely wide applications in national defense, aerospace measurement and control, nuclear physics detection, optical fiber communication, infrared optics, solar cells and other fields. This article will introduce the preparation method of germanium and its related applications in the AI era.

As an element of Group IVA, germanium has a series of unique physical and chemical properties. It has a similar lattice structure to silicon and is well compatible with complementary metal oxide semiconductor (CMOS) technology, which can effectively reduce manufacturing costs and improve device reliability. Germanium has a higher electron mobility, which is 10 times that of silicon. Electrons can move faster in germanium, which is conducive to achieving high response speed of devices. Its cut-off wavelength is between 1.7-2.2 microns, making germanium very suitable for manufacturing infrared detectors and photodetectors. By selecting different doping levels and manufacturing processes, the cut-off wavelength of the germanium detector can be effectively adjusted to make it suitable for applications in specific bands.

Synthesis of Germanium

1. Hydrometallurgical method

At present, there are three main types of raw materials for extracting germanium: germanium concentrates produced in the process of non-ferrous metal smelting, germanium-rich products produced after the combustion of germanium-containing coal, and various wastes produced in the deep processing of germanium. The wet extraction of germanium includes leaching, chlorination distillation, neutralization precipitation, solvent extraction, ion flotation, carrier liquid membrane and solid phase extraction. The leaching of zinc refining residues mainly uses inorganic acids, while the leaching of coal ash uses organic ligands. Germanium is different from ordinary metal cations. It exists in the form of neutral substances in acidic pH values. Therefore, in the process of solvent extraction and ion exchange, organic ligands can be used to form anionic germanium ligand complexes, thereby separating substances by anion exchange. Although germanium only exists in one stable oxidation state in the liquid phase, namely IV, it can exist in many forms. The form of germanium in the solution mainly depends on the pH value, the concentration of germanium, the type and concentration of anions, and the extractant. Various extractants are usually used to recover germanium from the liquid phase based on the physical and chemical properties of the germanium-containing liquid phase, such as flash point, density and solubility.

(1) Acid leaching of germanium: Acid leaching of germanium generally uses brine to leach zinc-germanium waste residue instead of sulfuric acid, because SiO2 and Zn2SiO4 will be formed during the roasting process of zinc ore, which will lead to the formation of silica gel during the leaching process. The process can be summarized as three steps: chlorination, hydrolysis and reduction. Chlorination is the preparation of GeCl4. This step is mainly achieved by taking advantage of the significantly different boiling points of GeCl4 and other impurities. At present, the commonly used methods for preparing germanium tetrachloride include chloride distillation and chloride volatilization. GeO2 is not only a raw material for preparing metallic germanium, but also can be used in the electronics industry, semiconductor materials and other fields. In order to obtain metallic germanium, GeCl4 needs to be used for hydrolysis reaction. In order to obtain high-purity GeO2, the hydrolysis water is often required to be electronic grade water, and the hydrolysis raw material is high-purity GeCl4. In the chlorination, hydrolysis, and reduction methods, the metallic germanium generated through reduction is achieved by using GeO2 as the raw material and hydrogen as the reducing agent. GeO2 will first be reduced to GeO and then to Ge. At a temperature of 700°C, GeO is easily volatile, so the reaction temperature needs to be controlled at 600-650°C.

At present, this method has some shortcomings, such as: the preparation process of germanium dioxide is too long, requiring a series of long process processes such as hydrolysis, filtration, cleaning, calcination, grinding, and screening; the preparation process involves material transfer, and it is easy to introduce new impurity elements wait. These problems have become the key obstacles to the preparation of high-purity materials. It is difficult to achieve the preparation of ultra-high-purity germanium using this method. How to effectively avoid the appearance of impurities in the process and reduce the steps of the process are the hot spots for subsequent research on this method.

(2) Solvent extraction: Solvent extraction is currently one of the main methods for extracting germanium from zinc-germanium leachate. Kelex100 is a relatively classic extractant, but its stability is poor and it is easily oxidized and decomposed. During the extraction process, copper and iron in the zinc-germanium leachate are easily extracted. 7815 extractant can effectively extract germanium from zinc-germanium leachate and is widely used in production. However, due to its high viscosity and easy emulsification, it needs to be added with a modifier and a diluent for use. N235, as an amine extractant, has the characteristics of low raw material price and high extraction rate. Like 7815, it is widely used in the extraction of germanium.

Solvent extraction has the advantages of good selectivity and high extraction rate in the research direction of extracting germanium from zinc-germanium leachate, but it also has the problems that the extractant has high requirements for the concentration, temperature and acidity of the extraction; the extractant has high viscosity and is easy to emulsify; the extractant cannot be recycled and has high cost; the preparation process is long. Compared with other methods currently used in China, it has great disadvantages.

(3) Ion exchange: The ion exchange method is to add ion exchangers to the zinc-germanium leaching solution to exchange ions with the ions in the liquid, thereby achieving the purpose of extracting germanium. This method is more suitable for solutions with germanium ion concentrations greater than 1×10-5mol/L. Among them, ion exchangers are divided into organic and inorganic types.

The ion exchange method has the advantages of being green and environmentally friendly, high germanium recovery rate, good selectivity, effective removal of impurity ions, low water solubility, and not easy to emulsify. However, due to the defects of ion exchangers such as high price, high cost, difficulty in recycling, and complex process flow, it is difficult to promote it on a large scale in industrial applications.

(4) Neutralization precipitation: Neutralization precipitation can be roughly divided into zinc powder replacement precipitation method, neutralization precipitation method and tannin precipitation method. Tannin precipitation method is the most mature method at present. Compared with other processes, it has the advantages of high germanium recovery rate, green environmental protection and rapid reaction. Although tannic acid can effectively recover germanium, the amount of tannic acid required in actual production is huge, which can easily lead to excessive production costs and impose a heavy burden on enterprises. Secondly, the chemical properties of tannic acid are unstable. When the temperature is too high, it will react with germanium and other impurity ions to form metal complexes. Therefore, before using the tannin method to precipitate germanium, it is necessary to inhibit side reactions and remove impurity ions. How to reduce the amount of tannic acid while maintaining the germanium recovery rate is the focus of subsequent research on neutralization precipitation.

(5) Supported liquid membrane: Supported liquid membranes (SLMs) are porous membranes impregnated with solvent extractants, which are stabilized in the pores by capillary forces. The membrane is sandwiched between the feed and strip solution chambers, where the extractant acts as a carrier to transfer the target species from the feed phase to the strip phase. There are two common configurations of SLM: flat plate supported liquid membrane (FSSLM) and hollow fiber supported liquid membrane (HFSLM).

Like the ion exchange method, supported liquid membranes have the disadvantages of being expensive, high cost, and difficult to recycle. Currently, they are the main method for preparing germanium in laboratory research. Since supported liquid membranes have an extraction rate of nearly 100% for germanium, how to effectively solve the problem of high cost and difficulty in recycling of supported liquid membranes is the prerequisite for the large-scale development of supported liquid membranes in the future.

(6) Solid-phase adsorbents: Solid-phase adsorbents lack high selectivity and capacity for germanium. Traditional solid-phase adsorbents include mesoporous silica, mesoporous carbon, and metal-organic frameworks (MOFS), while new adsorbents include ion-imprinted polymers (IIPs) and magnetic nanomaterial-based adsorbents. Compared with liquid phase extraction, solid phase extraction has the advantages of low energy input, convenient deployment, low operating and maintenance costs, high adsorbent reusability, high extraction efficiency, and environmental protection. However, solid-phase adsorbents have the disadvantage of difficult separation. At present, there are few studies on the adsorption of germanium in the field of solid-phase adsorbents.

2.Pyrometallurgical method of germanium

The preparation methods of germanium are mainly divided into chemical vapor deposition method, disproportionation method, alloy method and aluminum chloride smelting method. The commonly used method for preparing metallic germanium in my country is to add alkali, such as sodium carbonate and sodium hydroxide, to the liquid phase containing rich germanium to convert germanium into germanate precipitate, and then obtain germanium tetrachloride through chlorination distillation method; or add zinc powder to cause replacement reaction; or through aluminum chloride smelting method; or through alloy method to smelt germanium-rich fly ash, and then obtain germanium tetrachloride through chlorination distillation method, and then perform hydrolysis reduction and other steps to obtain metallic germanium.

(1) Disproportionation method: only applicable to GeX2 materials (X is F, Cl, Br, I) such as germanium dichloride and germanium diiodide as raw materials. Germanium dichloride will undergo disproportionation reaction at 1000℃ to generate germanium tetrachloride and metallic germanium.

(2) Chemical vapor deposition method: It is divided into the preparation of germanium by thermal decomposition of germanium and the preparation of germanium by hydrogen reduction of germanium tetrachloride. Germane has the characteristics of poor thermal stability. At 160-280°C, it will slowly oxidize to produce hydrogen and germanium. It will completely decompose at above 350°C. When germane decomposes, it will form a layer of germanium metal film on the surface of the substrate. This metal film will have a strong catalytic effect on the decomposition of germane, accelerating the subsequent decomposition rate of germane, but this process is somewhat dangerous, so the decomposition of germane needs to be controlled at a lower temperature.

(3) Preparation of germanium by hydrogen reduction of germanium tetrachloride: High-purity hydrogen is used to bring germanium tetrachloride vapor into the reduction furnace, making the reaction more stable and less likely to introduce impurities during the reaction. At the same time, the lengthy step of hydrolyzing germanium tetrachloride into germanium dichloride is omitted, reducing the investment in equipment costs. This method is currently in the experimental research stage. In the absence of a catalyst, the one-time conversion rate of germanium can reach up to 31.89%. This method is mainly based on the idea proposed by the preparation method of polysilicon. Its feasibility has been verified and will become a hot topic in the field of germanium preparation research in the future.

Germanium related applications in the AI era

1、Application of Germanium in Integrated Circuits

Integrated circuits are the core of modern electronic equipment, providing necessary hardware support for the operation of AI algorithms. After years of development, the manufacturing process of traditional silicon-based integrated circuits is gradually approaching the physical limit, and the performance development speed is also gradually slowing down. . Germanium has high electron mobility, and electrons can move quickly in germanium materials. Compared with traditional silicon-based materials, germanium can achieve faster signal transmission and information processing speeds. When germanium is introduced into the chip manufacturing process, it can significantly improve the performance of transistors and significantly increase the computing efficiency of the entire chip. In addition, there is good compatibility between germanium and silicon, which can form a germanium-silicon alloy. This material not only inherits the stability and mature manufacturing process of silicon, but can also give full play to the high electron mobility characteristics of germanium and realize chip implementation. Performance optimization. For example, in advanced complementary metal oxide semiconductor (CMOS) technology, the use of germanium-silicon channels can effectively reduce resistance and improve current drive capabilities, allowing AI processors to complete more complex computing tasks in a shorter time.

2. Germanium is used in photodetectors

In AI systems, accurate perception and rapid response processing of images and light signals are the key to achieving efficient and intelligent decision-making. As an important device for converting light signals into electrical signals, the performance of photodetectors directly affects the perception ability of the entire system. Germanium performs very well in the field of photodetection due to its excellent photoelectric conversion performance. Compared with other common photoelectric materials, germanium has a faster response speed and higher sensitivity, which means that it can respond to light signals in a very short time and accurately convert them into electrical signals, reducing signal delays and distortion. In the AI era, machine vision and autonomous driving require real-time and accurate perception of complex and changing environments. Photodetectors made of germanium can maintain good performance under low light conditions and can capture weak light signals in time. Provide AI systems with richer and more accurate environmental information elements, greatly improving the accuracy of image recognition and the reliability of autonomous driving systems.

3. Application of Germanium in the medical field

Despite the controversy, organic germanium is safe for humans and has unique physiological activities and health benefits. It is currently being valued and explored by medical scientists around the world. The structure of this compound contains three germanium-oxygen connecting chains, which enables it to supply a large amount of oxygen to every part of the body to enhance immunity and eliminate toxins and waste: it can also delay the aging process and effectively curb the occurrence of cancer and other key functions. Therefore, based on this characteristic, this substance has been widely used in the prevention and treatment of various diseases, including as a means of regulating high blood pressure, high cholesterol, controlling blood sugar, relieving skeletal muscle pain, improving cardiovascular system diseases, and also suitable for improving or preventing memory loss in the elderly, or stroke caused by cerebral vascular blockage.

Based on its unique physical and chemical properties, the application potential of germanium in the AI era cannot be underestimated. At present, due to the scarcity and high price of germanium, the research on germanium is still in its early stages, but it is believed that with the continuous development of science and technology, people can solve the above problems and find more application directions for germanium.