https://www.sciencedaily.com/releases/2021/09/210909123916.htm

Gallium nitride (GaN)-on-diamond shows promise as a next-generation semiconductor material due to the wide band gap of both materials, allowing for high conductivity, and diamond's high thermal conductivity, positioning it as a superior heat-spreading substrate. There have been attempts at creating a GaN-on-diamond structure by combining the two components with some form of transition or adhesion layer, but in both cases the additional layer significantly interfered with diamond's thermal conductivity -- defeating a key advantage of the GaN-diamond combination.

"There is thus a need for a technology that can directly integrate diamond and GaN," states Jianbo Liang, Associate Professor of the Graduate School of Engineering, Osaka City University (OCU), and first author of the study, "However, due to large differences in their crystal structures and lattice constants, direct diamond growth on GaN and vice versa is impossible."