[Industry Knowledge] Introduction to Semiconductor Crystals in Materials Science

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Semiconductor materials are the cornerstone of the modern semiconductor industry and microelectronics industry. From a physical point of view, it refers to a class of materials whose electrical conductivity is between that of conductors and insulators.

There are many types of semiconductor materials, which can be roughly divided into three types: inorganic semiconductor crystals, organic semiconductor materials and amorphous semiconductors. At present, amorphous semiconductor materials have great application prospects in solar cells. But overall, inorganic semiconductor crystals still dominate semiconductor materials.

Inorganic semiconductor crystals can be further divided into three categories: elemental semiconductors, compound semiconductors, and solid solution semiconductor crystals. Elemental semiconductor crystals mainly include silicon, germanium, and selenium single crystals; compound semiconductors can be divided into binary, ternary, and quaternary crystals. Binary compound semiconductor crystals are composed of two elements and are of various types, including III-V group, such as GaAs, GaN, etc.; II-VI group, such as ZnSe, HgS, etc.; IV-IV group, such as SiC, etc. In addition, there are lead compounds and oxide semiconductor crystals (such as ZnO). Binary compound semiconductor crystals are widely used in the field of optoelectronics. Ternary compound semiconductor crystals are represented by AlGaAs and GaAsP, which are widely used in the production of light-emitting tubes and solid-state lasers (LDs).

Silicon single crystal

Silicon single crystal is the most important element semiconductor crystal, with large output, fastest development and widest application. At present, more than 95% of semiconductor devices in the world are made of silicon materials. Silicon single crystal has metallic luster, hard and brittle, melting point is 1420℃; intrinsic resistivity at room temperature is 2.3×105Ω/cm. It is chemically stable at room temperature, insoluble in most acids, and active at high temperatures. Silicon is a typical multi-gap semiconductor. The bandgap width at room temperature is 1.121eV. Silicon materials are easy to highly purify, reaching more than 12 nines. The upper limit of the working temperature of devices made of silicon single crystal is 250℃.

The dislocation-free silicon single crystal growth technology is the foundation of the entire silicon semiconductor industry. Silicon single crystals can be grown using the CZ method, the MCZ method, the FZ method, and the vapor phase epitaxy method. Among them, the CZ method is the most mature and can produce silicon single crystals with a diameter of up to 16 inches (400mm).

Silicon carbide crystal

SiC is the main third-generation semiconductor material. Compared with single crystal materials such as the first-generation semiconductor Si and the second-generation semiconductor GaAs, SiC crystals have the characteristics of large bandgap width, high thermal conductivity, large electron saturation drift rate, high critical breakdown electric field, low dielectric constant, and good chemical stability. It has broad application prospects in high-frequency, high-power, high-temperature resistant, radiation-resistant semiconductor devices, ultraviolet detectors, and short-wave light-emitting diodes. Devices made of it can be used at high temperatures above 600°C.

SiC crystals are made of densely packed SiC tetrahedrons. Due to different stacking methods, SiC has more than 200 different crystal forms, but only a few such as 3C, 2H, 4H, 6H and 15R can exist stably. Phase diagram studies have shown that SiC sublimates at 2830°C under normal pressure and cannot form a liquid state, so silicon carbide crystals are mainly grown by sublimation.

Zinc oxide (ZnO) single crystal is a multifunctional crystal material with semiconductor, luminescence, piezoelectric, electro-optical and other applications. It has a wurtzite structure, a bandgap of 3.4eV at room temperature, an exciton binding energy of up to 60MeV, and a wavelength of emission shorter than that of GaN blue light, which can further increase the density of optical storage. Therefore, lasers made of ZnO have great application prospects in improving optical storage.

Zinc oxide crystals

The band edge emission of zinc oxide is in the ultraviolet region, which is very suitable as an excitation light source material for white light LEDs, highlighting the important position of ZnO in semiconductor lighting engineering. Compared with other wide band gap materials such as SiC and GaN, ZnO has many advantages such as abundant resources, low price, high chemical and thermal stability, better resistance to radiation damage, and is suitable for long-life devices. In addition, the physical properties of ZnO and GaN are very similar, and its lattice mismatch is very small, making it the most ideal substrate material for GaN crystal growth.

Zinc oxide is a uniformly molten compound with a melting point of 1975°C. Due to the high volatility of ZnO at high temperatures, it is difficult to obtain ZnO single crystals using traditional melt growth processes such as the Czochralski method. At present, the main methods for growing ZnO single crystals are slow cooling, hydrothermal, and vapor phase growth. Using the hydrothermal method, ZnO crystals can be grown from a mixed aqueous solution of KOH and LiOH. The crystals are light green or light yellow with good integrity, but the size is not large enough to meet the needs of industrial applications.

FEMAG Software Introduction:

The Belgian FEMAG software is the world's first commercial crystal growth numerical simulation software, developed in the 1980s by Professor F. Dupret, a world-renowned expert in fluid mechanics and crystal growth modeling and the University of Leuven. FEMAG has the most advanced and efficient crystal growth simulation technologies in the world, such as the Czochralski method, the zone melting method, and the crucible descent method, which are used in the fields of IC, photovoltaic solar energy, semiconductors, sapphire, etc. ONSEMI, Siltronic, Kute, Nexolon and other international top high-tech material companies are all FEMAG users.

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