Surface Zeta Potential and Diamond Seeding on Gallium Nitride Films.

Soumen Mandal,Evan L H Thomas,Menno J Kappers,Callum Middleton,Oliver A Williams,Rachel A Oliver,James T Griffiths,Martin Kuball,David J Wallis,Lucy E Goff,Laia Gines,Stephen A Lynch

doi:10.1021/acsomega.7b01069

Abstract

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 1011 cm–2. This technique removes the requirement for a low thermal conduction seeding layer like silicon nitride on GaN.

Highlights

With the high breakdown voltage and current handling ability, gallium nitride (GaN) high electron mobility transistors (HEMTs) are the current benchmark for high-power, highfrequency applications.[1,2] the heat generated during high power density conditions limits the use of such devices, with Lee et al.[3] demonstrating that small increases in the operating temperature can lead to drastic reductions in the device lifetime
In the majority of cases GaN HEMT layers are grown on the Ga-face, and the diamond heat spreading layer must be produced on the back N-face
The results from the ζ potential study of the GaN surface and diamond seeds show that such conditions are met when the seeds are Hterminated and the pH of the solution is close to 8

Summary

INTRODUCTION

With the high breakdown voltage and current handling ability, gallium nitride (GaN) high electron mobility transistors (HEMTs) are the current benchmark for high-power, highfrequency applications.[1,2] the heat generated during high power density conditions limits the use of such devices, with Lee et al.[3] demonstrating that small increases in the operating temperature can lead to drastic reductions in the device lifetime. To realize long lifetime and high performance of GaN electronics, it is essential to effectively extract heat from the devices. Polycrystalline diamond can be grown on GaN through the use of an adhesion layer.[10,11] the polycrystalline diamond has excellent thermal properties,[12] the poor thermal conductivity of the typically amorphous adhesion layer presents a barrier to the extraction of heat from the devices.[13] it is crucial to grow the diamond layer directly on to the surface of the GaN to provide more effective thermal management. With a similar large difference in the surface energy[19] between diamond and GaN with a value of ∼2 J/m2, a seeding technique is required for diamond thin-film growth on this compound.

RESULTS AND DISCUSSION

CONCLUSIONS

EXPERIMENTAL SECTION

■ ACKNOWLEDGMENTS

■ REFERENCES