Influence of N2 flux on the improvement of highly c-oriented GaN films on diamond substrates

► Diamond is currently one of the most promising materials as substrates for SAW devices due to its excellent mechanical, thermal, electrical, and chemical properties. Especially diamond has the highest sound velocity and the highest thermal conductivity. However, the diamond is not a piezoelectric material, it is necessary to deposit the piezoelectric films on the diamond films for SAW devices. And the GaN is currently one of the most promising materials for SAW devices due to its high SAW velocity, piezoelectric coupling, chemical stability and excellent thermal, by combining the virtue of diamond as substrate and GaN as piezoelectric film, the GaN/diamond structure will offer an attractive means for high frequency SAW devices with sufficient power durability. In this paper, the high-quality GaN films are deposited on freestanding thick diamond films by electron cyclotron resonance plasma-enhanced metal organic chemical vapour deposition (ECR-PEMOCVD) at different N2 fluxes and the influence of N2 flux on the properties of GaN films is systematically investigated by X-ray diffraction analysis (XRD), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM) and Hall effect measurement (HL). The results show that the high-quality GaN films with small surface roughness of 4.5 nm and high c-orientation are successfully achieved at the optimized N2 flux of 90 sccm. ► In this study, by combining the virtue of the highest sound velocity of diamond as substrate and the high-quality GaN as piezoelectric film are the research highlights for application of SAW devices. And the high-quality GaN films with small surface roughness and high c-orientation are successfully achieved on freestanding CVD thick diamond substrates, which is the key to solve the problem of technology and obtain the important experimental results.