The composition of sapphire is aluminium oxide (Al2O3), which is formed by covalent bonding of three oxygen atoms and two aluminum atoms, and its crystal structure is a hexagonal lattice. It is often utilized in A-Plane, C-Plane and R-Plane. Because sapphire has a wide optical penetration band from near ultraviolet light (190nm) to mid-infrared light, and it has excellent light transmittance, so it is widely used in optical components, infrared devices, high-intensity laser lens materials and photomask materials. It has the characteristics of high sound velocity, high temperature resistance, corrosion resistance, high hardness, high light transmittance, and high melting point (2045℃). Sapphire is a very difficult material to process, so it is often used as a material for optoelectronic components. At the same time, sapphire meets the high temperature resistance requirements in procession of the GaN epitaxy, so it is often made into LED sapphire substrates.
Sapphire crystals mainly have the following two craftsmanships:
1. Czochralski method, referred to as CZ. The raw materials are first heated to the melting point and then melted to form melt, then a single crystal seed is used to contact the surface of the melt, and supercooling is formed at the solid-liquid interface between the seed crystal and the melt due to difference of the temperature. Melt begins to solidify on the surface of the seed crystal and grow a single crystal with the same structure as the seed crystal. At the same time, the seed crystal is pulled up slowly and rotated at a certain speed. As the seed crystal is pulled up, the melt gradually solidifies on the liquid-solid interface of the seed crystal, and then forms an axially symmetrical unit crystal ingot.
2. The Kyropoulos method, referred to as KY. The principle is similar to that of the Czochralski crystal pulling method. The raw material is heated to the melting point and then melted to form a melt, and then a single crystal seed (Seed Crystal, also known as a seed crystal rod) contacts the surface of the molten soup. A single crystal with the same crystal structure as the seed crystal begins to grow on the solid-liquid interface of the seed crystal. The seed crystal is pulled up at a very slow speed, but the seed crystal is pulled up for a period of time to form a crystal neck. After the solidification rate of the interface of melt and seed crystal are stable. Only the cooling rate is controlled to gradually solidify the single crystal from above to the bottom, the seed crystal no longer pulls up or rotates and finally solidifies into a single crystal ingot.
After the sapphire crystal is grown, it can be processed into sapphire wafers, sapphire ingots, etc. for better application.