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c-plane sapphire (c-Sap) is most popular substrate for polar (Al, Ga)N growth, where it is known that the m-axes of sapphire and (Al, Ga)N are rotated by 30° to minimize lattice mismatch. On the other hand, it has been reported that the m-axes of sapphire and nitrides can be parallel with each other when grown on an a-plane sapphire. This epitaxial relation is beneficial for the laser cavity formation by cleavage. In this work, we demonstrated c-plane AlN/a-plane sapphire (c-AlN/a-Sap) templates by means of sputtering and high-temperature annealing [4]. X-ray diffraction (XRD) measurements revealed the epitaxial relation of a-Sap [1–100] //c-AlN [1–100] as expected from previous works. As the film thickness increased, the rocking curve width of (10–12) XRD improved, and 214 arcsec was obtained at the crack-free film thickness of 300 nm. These characteristics are attractive as an AlN template applicable for AlGaN-based DUV optical devices.

Diamond is an attractive widegap semiconductor for power devices due to the bandgap of 5.5 eV and high hole conductivity. Quantum sensing by nitrogen-vacancy (NV) centers has also been focused on in recent years. On the other hand, (Al, Ga)N has been extensively studied for deep ultraviolet LEDs and high electron mobility transistors, whereas the poor p-type conductance limits the performance of bipolar devices. Hence, the heterogeneous integration of diamond and (Al, Ga)N is expected to realize efficient carrier injection into widegap bipolar devices.