The single crystal substrate material refers to a single crystal wafer for epitaxial growth of a crystal thin film. And the term “epitaxy” refers to another directional growth of another single crystal on the surface of a single crystal under certain conditions. With the continuous development of science and technology, especially the rise and development of the optoelectronics industry, the performance and quality of thin films have become increasingly demanding. The original substrate materials are far from meeting the requirements, so various single crystal materials are used as substrates. At the right time, the scale of its industry has been expanding, and the research field is constantly expanding. Monocrystalline silicon materials are the preferred substrate materials for many thin films due to their compatibility with microelectronic devices. Some of the same thin films grown on various substrates can obtain the best performance or the most economical benefit. For example, GaN thin film substrates include SiC, Al2O3, ZnO, Si, and LiAiO2. Monocrystalline substrate materials are the basis of the optoelectronics industry.

As a substrate material, the single crystal has the following basic characteristics: stable physical and chemical properties, easy access to large-size single crystals, high thermal conductivity, small thermal expansion coefficient, good heat resistance, and good processability.

Types of single crystal substrates

• SiNx

  SiNx thin films have high hardness, corrosion resistance, high temperature resistance, good thermal conductivity and insulation, and excellent photoelectric performance. Therefore, SiNx thin films have been widely used in the fields of microelectronics and micro-mechanical systems.

• GaAs

  Gallium arsenide (GaAs) is a III-V compound semiconductor material that can operate at higher temperatures and greater directional voltages. It is the preferred material for the manufacture of high-power devices. Its electron mobility is 6 times that of Si, and its operating frequency is high. It is an ideal material for manufacturing high-speed integrated circuits and high-speed electronic devices.

• Al2O3

  The Al0.32Ga0.78N/GaN single-crystal thin film grown by epitaxial growth on a sapphire (mainly Al2O3) substrate using metal organic chemical vapor deposition (MOCVD) technology is the most preferred material for the preparation of high temperature, high frequency, and high power devices. The material system has great application potential in satellite, radar, communications and other fields.

• SrTiO3

  Strontium titanate (SrTiO3) is a widely used electronic functional ceramic material, which has the advantages of high dielectric constant, low dielectric loss, and good thermal stability. And it is widely used in the electronic, mechanical and ceramic industries. At the same time, as a functional material, strontium titanate has excellent photocatalytic activity, and has unique electromagnetic properties and redox catalytic activity. Strontium titanate has also been widely used in the photocatalytic decomposition of water to produce hydrogen, photocatalytic degradation of organic pollutants and photochemical batteries. In addition, it is often cut into a synthetic emerald-type gemstone and is a very good diamond substitute.

Applications

• Luminescent materials: Semiconductor light-emitting diodes (LEDs) produce white light, and because of their energy-saving and environmentally friendly characteristics, they have become the most valuable new light source in this century. Monocrystalline substrate materials play a key role in LEDs. At present, the commonly used substrates are SiC, Al2O3 and Si. The melting point of SiC single crystal is very high, about 2700°C, so its chemical properties are relatively stable. SiC substrate materials are available in 6H type and 4H type, which makes production control more difficult. Until 1991, the 6H-SiC type began to be commercialized, and the commercialization of 4H-SiC started from 1994. The SiC substrate material laid the foundation for the birth of the LED in 1996.

• Superconducting materials: Superconducting materials are generally prepared on an ultra-smooth surface single crystal substrate. The so-called ultra-smooth surface is a surface with a roughness of less than 1 nm. It is characterized by no surface damage or scratches and no subsurface damage. This ultra-smooth surface single crystal substrate processing is gradually infiltrating into many fields such as superconductivity, giant magnetoresistance, ferroelectric thin films and the like. The quasi-cubic structure of LaAlO3 at normal temperature is a typical super-smooth surface single crystal substrate with a lattice constant of 0.379 nm. LaAlO3 is often used as a substrate for high-temperature superconducting material YBCO.