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UHPA method

 

High pressure high temperature equipment

High pressure high temperature equipment, typical experimental setup for gallium nitride (GaN) crystal growth with the high nitrogen pressure solution (HNPS) method can be used for ultra-high pressure annealing (UHPA) Vertically positioned, technological gas pressure chambers (reactors) with an internal diameter of 4, 6 and 10 cm (allowing graphite, boron nitride or alumina crucible with working volume of 10, 25 and 150 cm3) can be applied. Maximum gas (nitrogen or argon) pressure is 1 GPa (10 000 atmospheres). Multizone cylindrical graphite furnaces, capable of reaching temperatures up to 2000 K, can be placed inside the gas pressure reactors. The chambers are equipped with additional systems necessary for annealing in vacuum, cooling of the reactor, electronic stabilization and programming of pressure and temperature. To monitor the temperature during the experiments, PtRh6%–PtRh30% thermocouples are used. They are arranged along the furnace and coupled with the input power control electronic systems. The pressure is measured by manganin gauges positioned in the low temperature zone of the reactor. The pressure and the temperature are stabilized with an accuracy of 1 MPa and 0.1 K, respectively.

Typically a sample (covered by a special cap if needed) is placed in the crucible and heated in the furnace inside the high pressure reactor with a constant rate (from 0.1 K/h to 1600 K/h) to a given temperature (from 500 K to 2000 K). Then, the system is annealed at these conditions under high nitrogen pressure (1 GPa or less) for a given time from 0.1 sec to 1000 h. After that, the furnace is cooled down at a constant rate (maximum 200 K/min), the system is decompressed, and the sample is removed.
 

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