Historically, semiconductors are famous for the invention of transistors. But semiconductors are not all crystals.
As we all know, materials are divided into two categories: crystalline and amorphous.
Crystal is a solid with internal particles arranged periodically and repeatedly in three-dimensional space; In other words, crystals are solids with a lattice structure. The so-called lattice structure refers to the regular arrangement of internal particles (atoms, ions or molecules) to form a certain geometric figure. The basic element of crystal is symmetry. The ideal shape and internal structure of the crystal have specific symmetry. An important feature of crystal is that its appearance is a regular geometric shape. The crystals grown in ideal environment should be convex polygons.
Things that look like crystals, such as glass and amber. There is no lattice structure, that is, they do not repeat periodically. This solid is called amorphous or amorphous.
Crystals are also different from crystals. Crystals can be classified according to their sources and binding properties. Crystals are divided into rock crystal (gems, ice, sand, etc.). ) and intraocular lens (all kinds of intraocular lens materials, etc. According to their sources. Crystals are divided into: atomic crystals, such as diamond; Ionic crystals, such as NaCl；; Molecular crystals, such as ice; Metal crystals, such as copper.
Rock crystal, or rock crystal mineral, is a natural simple substance or compound with certain chemical composition and crystal structure. Synthetic crystals are synthetic or artificial crystals.
Synthetic crystals are artificial crystals with natural counterparts. On the contrary, artificial crystals have no natural counterparts, such as artificial strontium titanate, garnet (YAG) and garnet (GGG).
People's common crystals are crystal, halite, sucrose and so on. In the eyes of ordinary people, crystal, like crystal and halite, has a regular geometric polyhedron shape.
Both crystalline semiconductors and amorphous semiconductors, including polycrystalline semiconductors, are useful. Such as silicon solar cells, including monocrystalline silicon solar cells, amorphous silicon solar cells, polycrystalline silicon solar cells and the like.
(2) Crystals and precious stones
The regular geometric shape and crystal-clear and beautiful color of crystal make people think of gems at once.
Common gems classified by crystal system are:
Advanced crystal family, such as diamond, garnet, spinel, etc. Have equal axial symmetry;
Medium crystal families, such as emeralds and aquamarine with hexagonal symmetry; Triple symmetry ruby, sapphire, tourmaline and crystal; Zircon with tetragonal symmetry, etc.
Low-grade crystal family, such as obliquely symmetric topaz, olivine and gold emerald; Nephrite, jadeite and diopside with monoclinic symmetry; Labrador and moonstone with triclinic symmetry.
Pay attention to the difference between precious stones and jadeite here. Gems, such as diamonds, rubies and sapphires, are single crystals, that is, crystals composed of a single mineral. Emerald, such as jadeite, nephrite and jadeite, is a polycrystalline aggregate, that is, an aggregate composed of one or more minerals.
(3) Semiconductors and Gems
"Diamonds are eternal" is the advertising word used by De Beers, the jewel king, in 1939.
The diamond here is diamond, or carbon (C) with diamond structure. Diamond is the hardest gem known at present.
Pure diamonds are colorless. Blue diamond is doped with a small amount of boron (B), while purple diamond is doped with a small amount of nitrogen (N), boron (B) and hydrogen (H) atoms.
If such a precious thing can be made artificially, what a great wealth temptation it is! In fact, people have been trying to make synthetic diamonds for a long time.
1893, French scientist Henri Moissan (1852- 1907) announced to the world that he had successfully made the world's first synthetic diamond from graphite. But when someone questioned that he had doubts or could not copy, he refused on the grounds of confidentiality and patent. In fact, he didn't really make diamonds out of graphite, but he didn't cheat. It is said that Movasan firmly believed that diamonds can be made under normal pressure and asked his assistant to try again and again. Later, the assistant was really bored, so he put a diamond in the stove in advance. Movasan didn't know, and thought the experiment was really successful. It was not until 1955 that the American General Motors Company successfully developed synthetic diamonds.
Besides diamonds, sapphires and rubies (red and blue corundum) are often used as substrates in the semiconductor industry. Sapphire and ruby are mainly composed of alumina (Al2O3).
Pure alumina is colorless, and the colors of sapphires and rubies are caused by mixed metals, such as sapphires: alumina+iron (Fe) and titanium (Ti); Ruby: alumina+chromium. Of course, sapphire and ruby can now be synthesized artificially, and they don't need to be colorful when used as substrates, so metal doping is avoided.