Adherent β-Ga2O3 thin films on single crystal diamond (001) substrates enabled by (AlxGa1−x)2O3 buffer layers

Diamond is an attractive substrate choice for the growth of gallium oxide for high-power device applications due to its high thermal conductivity. However, the cubic crystal structure of diamond is very different from that of monoclinic β-Ga2O3. Adding to the complexity, there is a large surface energy difference between the two materials, and a high-temperature oxide environment is required for Ga2O3 growth. Here, we demonstrate a viable pathway that enables thick adherent Ga2O3 layers to be grown epitaxially on diamond (001) substrates, using metal–organic chemical vapor deposition. This growth is achieved using an intermediary (Al0.06Ga0.94)2O3 (AGO6) buffer layer. Omission of the strain management buffer results in Ga2O3 films that exfoliate into membranes for thicknesses greater than about 500 nm. Implementation of the buffer layer allows for the alleviation of the excess strain energy developed within the grown film and assists in improving film quality, increasing grain size, reducing dislocations, and providing epitaxially textured thin films relative to layers without the buffer. Adherent 750-nm-thick β-Ga2O3 epitaxial layers have been achieved using the AGO6 buffer, with a full-width at half-maximum of 1.36° and a root-mean-square roughness of 6.24 nm. The thermal conductivity of the β-Ga2O3 thin films with and without the AGO6 buffer was measured to be 6.0–6.5 W/mK. Thus, integration of the monoclinic gallium oxide with the diamond cubic substrate using the intermediary buffer layer improves the crystal quality but does not impact the thermal conductivity, suggesting the future feasibility of using diamond substrates for a wide range of Ga2O3 device applications.