Growth of high quality AlN on sapphire by using a low-temperature AlN interlayer

Aluminum nitride is a material of great potential for high power electronic devices, UV photonic devices as well as acoustic devices. However, the lack of a good crystal growth technology for bulk material and substrate hinders the development of these AlN-based devices. While AlN has been successfully grown on sapphire substrate for some time, the presence of a large number of dislocations in the material is still a major barrier to overcome [1]. In this work, we demonstrate a low-dislocation-density AlN template on sapphire by inserting an AlN interlayer by metal-organic chemical vapor deposition. The main idea of our approach is to change the growth mode in the course of the epitaxial growth by decreasing growth temperature and changing V/III ratio. As the growth mode changes, dislocations tend to be redirected and/or form dipole half loops via annihilation processes [2]. The etch-pit-density of the AlN templates is reduced from 3.6×10⁹ cm^-2 to 1.7×10⁹ cm^-2. Accordingly, the full width at half maximum of the (0002) x-ray rocking curve is reduced from 37 arcsec to 12 arcsec. The result indicates that the AlN template has low screw and mixed type dislocations. AlGaN/GaN Schottky diodes fabricated on this high quality AlN template exhibit very high breakdown voltage (> 2000 V), which sets a record-high figure of merit of 1.37 GW/cm².