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Sunday, 19 Aug 2018

ZnO project

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The crystals of ZnO have the unique combination of semi-conductive, piezoelectric, optical and temperature properties in comparison with the other crystals. These properties provide for successful application of zinc oxide crystals in different fields of science and engineering (piezoelectric converters, optical wave guides, sensors - gas analyzers, opto- and acoustoelectronic devices, scintillators and many others).

With good reason ZnO is considered as the most promising semi-conductive system of the new millennium. Generally, the particular application of ZnO, as well as the other semiconductors, is defined by technological opportunities of its synthesis with the appropriate properties. At present time in the world the intensive researches on ZnO are being carried out in the following directions:

  • Light-emitting diodes and semi-conductor lasers for UV-area.

ZnO is a semiconductor having the properties similar to GaN. It demonstrates piezoelectric effect, has the forbidden bandwidth of 3,4 eV and exciton binding energy of 60 MeV that is perspective for optoelectronic application.

  • Spintronics. Only two wide bandgap semiconductors (GaN and ZnO) are suitable to make spintronics devices at room temperatures.
  • Acoustoelectronics. The usage of ZnO single crystals for manufacturing of SAW filters and SAW resonators is rather perspective.
  • Touch engineering.

The existence of linear dependence lnR (1/T) in the range of 100-450° C allows using ZnO in temperature sensors, while the dependence of resistance on load and illumination allows applying zincite in pressure sensors and devices of fire alarm system.

  • High-temperature devices.

Elastic, dielectric, piezoelectric properties of zinc oxide are differed by the improved stability up to temperature 700 K. The absence of phase transitions and radiation resistance makes this material perspective for application at radiation and high temperatures.

  • Automatic systems.

The specific volt-ampere characteristics of zinc oxide can be widely used in manufacturing of automatic systems and electric engineering equipment (varistors, sensors, actuators, automatic switches).

  • High-quality crystalline substrates for GaN.

ZnO is alternative to sapphire, as it has not only a proportional crystalline substrate and close factors of thermal expansion, but also meets in the greater degree the requirements to electro-physical parameters.

Zinc oxide (ZnO) synthetic single crystals

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.

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