The impact of seeding of the diamond growth on the microstructural properties of GaN-on-diamond wafers was studied using in situ focused ion beam cross-sectioning and scanning electron microscopy imaging. Microstructural studies revealed that the seeding conditions are a critical parameter to obtain an optimal material, allowing the manufacture of GaN-on-diamond wafers with no microscopic defects and with structural stability under thermal annealing at 825⁰C. The use of the right seeding conditions also results in homogeneous thermal properties across four inch GaN-on-diamond wafers, which is of critical importance for their use for ultra-high power microwave electronic devices.
The measurement of ζ potential
of Ga-face and N-face gallium
nitride has been carried out as a function of pH. Both of the faces
show negative ζ potential in the pH range 5.5–9. The
Ga-face has an isoelectric point at pH 5.5. The N-face shows a more
negative ζ potential due to larger concentration of adsorbed
oxygen. The ζ potential data clearly showed that H-terminated
diamond seed solution at pH 8 will be optimal for the self-assembly
of a monolayer of diamond nanoparticles on the GaN surface. The subsequent
growth of thin diamond films on GaN seeded with H-terminated diamond
seeds produced fully coalesced films, confirming a seeding density
in excess of 10
11
cm
–2
. This technique
removes the requirement for a low thermal conduction seeding layer
like silicon nitride on GaN.
We demonstrate that GaN-on-diamond technology with an ultra-thin GaN buffer and interface layer offers excellent thermal resistance alongside good electrical performance. Two device sets were investigated, one with 354 nm thick GaN buffer and 17 nm thick interface layers, the other with 700 nm thick GaN buffer and 36 nm thick interface layers. The samples demonstrate excellent thermal resistances of 9 ± 1 K/(W/mm) and 10.0 ± 0.5 K/(W/mm), respectively. Trade-offs between GaN buffer thickness and effective thermal boundary resistance are discussed demonstrating pathways for the advancement of GaN-on-diamond technology. IV measurements show low trapping and reduced thermal non-linearity in devices with ultra-thin GaN layers.
Heat extraction from novel GaN/AlGaN superlattice castellated field effect transistors developed as an RF switch is studied. The device thermal resistance was determined as 19.1 ± 0.7 K/(W/mm) from a combination of Raman thermography measurements, and gate resistance thermometry. Finite element simulations were used to predict the peak temperatures and show that the three-dimensional gate structure aids the extraction of heat generated in the channel. The calculated heat flux in the castellations shows that the gate metal provides a high thermal conductivity path, bypassing the lower thermal conductivity superlattice, reducing channel temperatures by as much as 23%.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.