Oliver Williams1,Soumen Mandal1,Evan Thomas1,Jerome Cuenca1,Karsten Arts2,Harm Knoops2,3,Georgina Klemencic1,Henry Bland1,Chao Yuan4,Fabien Massabuau5,Rachel Oliver5,David Wallis5,1,Martin Kuball4
Cardiff University1,Technische Universiteit Eindhoven2,Oxford Instruments Plasma Technology3,University of Bristol4,University of Cambridge5
Oliver Williams1,Soumen Mandal1,Evan Thomas1,Jerome Cuenca1,Karsten Arts2,Harm Knoops2,3,Georgina Klemencic1,Henry Bland1,Chao Yuan4,Fabien Massabuau5,Rachel Oliver5,David Wallis5,1,Martin Kuball4
Cardiff University1,Technische Universiteit Eindhoven2,Oxford Instruments Plasma Technology3,University of Bristol4,University of Cambridge5
Efficient heat extraction in high power and high frequency devices is key towards full utilisation of materials like GaN, AlN and Ga<sub>2</sub>O<sub>3</sub>. The present technology of using SiC has allowed good device performances, but there is still room for considerable improvements. Replacing SiC(k<sub>SiC </sub>~ 360 – 490 W/m K) with diamond(k<sub>Dia </sub>~ 2100 W/m K) is one of the potential options. However, for any potential benefits to be had, the diamond layer should have thickness more than 50 microns. Here we will discuss the growth of diamond layers on wide band semiconductors. We have demonstrated the growth of diamond layer on GaN surfaces<sup>1</sup>. While it is difficult to grow thick adherent layer on the GaN surfaces due to absence of any covalent bond between GaN and diamond, the problem can be overcome by growing the diamond layer on AlN surface<sup>2</sup>. AlN acts as seed layer for GaN growth on silicon and a wide band gap semiconductor in itself as well. Finally, we have also demonstrated the growth of diamond on Ga<sub>2</sub>O<sub>3 </sub>single crystals<sup>3</sup>. In the case of Ga<sub>2</sub>O<sub>3</sub>, direct growth of diamond is not possible, and a thin interlayer is essential for the growth.<br/>Advances in growth technologies makes it possible to grow diamond on variety of substrates, however, to grow diamond on non-diamond substrate, a seeding or nucleation step is essential<sup>4</sup>. In the results presented here we have used a seeding technique called electrostatic seeding. To accomplish this, it is essential to know the surface charge of the substrates. We have determined the zeta potentials (which is an indicator of the surface charge) of the wide band gap materials used in these works, which determined the type of diamond seeds (positive or negative) needed for efficient seeding. AFM was used to determine the seed density on the surface of the substrates. The seeded wafers were introduced in microwave plasma chemical vapour deposition system for growth of diamond. For thick diamond layers on AlN we have determined the thermal boundary resistance between diamond and AlN<sup>2</sup>. The quality of diamond layers was determined by Raman spectroscopy, SEM etc.<br/>References<br/><sup>1</sup> S. Mandal, E.L.H. Thomas, C. Middleton, et al., ACS Omega <b>2</b>, 7275 (2017).<br/><sup>2</sup> S. Mandal, C. Yuan, F. Massabuau, et al., ACS Appl. Mater. Interfaces <b>11</b>, 40826 (2019).<br/><sup>3</sup> S. Mandal, K. Arts, H.C.M. Knoops, et al., Carbon N. Y. <b>181</b>, 79 (2021).<br/><sup>4</sup> S. Mandal, RSC Adv. <b>11</b>, 10159 (2021).