TaC Coating Crucible for AlN Crystal Growth

The third generation of semiconductor materials AlN belongs to the direct bandgap semiconductor, its bandwidth of 6.2 eV, with high thermal conductivity, resistivity, breakdown field strength, as well as excellent chemical and thermal stability, is not only an important blue light, ultraviolet materials, or electronic devices and integrated circuits, important packaging, dielectric isolation and insulation materials, especially for high-temperature high-power devices. In addition, AlN and GaN have a good thermal match and chemical compatibility, AlN used as GaN epitaxial substrate, can significantly reduce the defect density in GaN devices, improve device performance.

At present, the world has the ability to grow AlN ingots with a diameter of 2 inches, but there are still many problems to be solved for the growth of larger size crystals, and the crucible material is one of the problems.

The PVT method of AlN crystal growth in a high temperature environment, AlN gasification, gas-phase transport and recrystallisation activities are carried out in relatively closed crucibles, so high temperature resistance, corrosion resistance and long service life have become important indicators of crucible materials for AlN crystal growth.

Currently available crucible materials are mainly refractory metal W and TaC ceramics. W crucibles have a short crucible life due to their slow reaction with AlN and carbonisation erosion in C atmosphere furnaces. At present, the real AlN crystal growth crucible materials are mainly focused on TaC materials, which is a binary compound with the highest melting point with excellent physical and chemical properties, such as high melting point (3,880 ℃), high Vickers hardness (＞9.4 GPa) and high elasticity modulus; it has excellent thermal conductivity, electrical conductivity, and resistance to chemical corrosion (only dissolved in a mixed solution of nitric acid and hydrofluoric acid). The application of TaC in crucible has two forms: one is TaC crucible itself and the other is as protective coating of graphite crucible.

The TaC crucible has the advantages of high crystal purity and small quality loss, but the crucible is difficult to form and has high cost. The TaC-coated graphite crucible, which combines the easy processing of graphite material and the low contamination of TaC crucible, has been favoured by the researchers and has been successfully applied to the growth of AlN crystals and SiC crystals. By further optimising the TaC coating process and improving the coating quality, the TaC-coated graphite crucible will be the first choice for AlN crystal growth crucible, which is of great research value for reducing the cost of AlN crystal growth.