IŽÁK Tibor Institute of Physics of the ASCR, v.v.i.

Study on Nucleation and Early Growth of Diamond on GaN

Co-authors BABCHENKO Oleg, POTOCKÝ Štepán, VANKO Gabriel, VOJS Marián, KROMKA Alexander

Large band-gap materials, such as diamond or gallium nitride (GaN), are the prime candidates for a variety of sensor applications, particularly working at high temperatures and in harsh environments. Combination of diamond and GaN represents an attractive choice for high power electronic where diamond acts as heat spreader. In this study we investigate the diamond growth on GaN substrates by microwave plasma CVD. In fact, the GaN substrate is represented by 2 m thick AlGaN/GaN multilayer system deposited on Si substrate. We show that using a proper gas mixture is crucial a technological factor to keep the functionality of GaN HEMT devices. Addition of CO2 and N2 to CH4/H2 gas mixture is used to minimize damaging of GaN substrate. We also found that the gas mixture control the diamond morphology from nano- to polycrystalline character. Simultaneous study focuses on the diamond growth on GaN membranes. In this case, diamond nucleation is the most limiting technological step due to low mechanical stability of GaN membranes. We observed that standard nucleation techniques (ultrasonic seeding or bias enhanced nucleation) caused cracking of the membranes or not appropriate nucleation efficiency in the Z-depth of structures. Therefore we implemented PVA polymer consisting of diamond powder as seeding composite which resulted in a successful growth of diamond thin film. ACKNOWLEDGEMENTS: This work was supported by the GACR grant Nr. 14-16549P and by the Slovak Research and Development Agency, grant Nr. APVV-0455-12.