Zinc oxide single crystals having semi-conductive and piezoelectric characteristics are the promising materials for using in various fields of electronic engineering. Such properties of ZnO single crystals as the high values of both band gap width and electromechanical coupling coefficient, the absence of phase transitions and the radiation resistance up to 900 °C makes ZnO to be the promising material for the application in the fields where the application of quartz is limited.
Currently ZnO plates are basically used as a substrate for gallium nitride (blue laser and laser diodes) epitaxy due to its close unit cell dimensions in direction parallel to the pedion (monohedron) face.
We use the hydrothermal technique for zinc oxide single crystals growth. The advantage of hydrothermal technique is the low growth rate allowing to obtain homogeneous, defect-free material. In addition, this method can be used for increasing crystal size in prism direction and for increasing seed size. The last circumstance is very important because there are no the natural ZnO seeds.
As a result of many years of research it has been developed a technology of hydrothermal growth of ZnO single crystals in the laboratory autoclaves combined with corrosion-resistant inner container up to 16 liters in volume with highly concentrated alkaline solution. Currently the industrial technology for autoclaves protected by the inner containers (100 and 200 liters) is being developed.
Serial cycles of crystallization result in visually homogeneous, undoped crystals up to 450 gr. and up to three inches in size.
ZnO crystals are easily doped with Mn, Fe, Ni, Co, Al impurities. ZnO with small quantity of Mn2+ ions can absorb visible wavelengths except the red wavelengths. Therefore, these samples can be used as excellent optical filters.