9:30 AM - EN02.07.01
Diamond Growth on GaN Membranes Using Microwave Plasma Chemical Vapour Deposition
Oliver Williams1,Jerome Cuenca1,Matthew Smith2,Daniel Field2,Soumen Mandal1,Simon Fairclough3,Fabien Massabuau4,James Pomeroy2,David Wallis1,3,Rachel Oliver3,Iain Thayne5,Martin Kuball2
Cardiff University1,University of Bristol2,University of Cambridge3,University of Strathclyde4,University of Glasgow5
The integration of diamond on gallium nitride (GaN) has significant potential for improving the thermal management of high-power high electron mobility transistors (HEMTs). However, there are several challenges associated with the whole process of direct diamond growth onto GaN through microwave plasma chemical vapour (MP-CVD). A prevalent issue is that GaN does not adhere very well to diamond and therefore requires an interlayer that can form a stable carbide such as an aluminium or silicon containing layer (eg. AlN, AlGaN, SiN or SiC)1. Ultimately, one of the most significant challenges is that the diamond needs to replace the substrate (for example GaN-on-Si becomes GaN-on-Diamond), necessitating a lengthy wafer boding process to flip and expose the nitrogen polar side of a GaN/AlGaN stack for CVD diamond growth. This temporary carrier bonding and flipping process limits sample fabrication for principal studies to simply examine a CVD grown diamond on GaN/AlGaN interface.
We have presented several published works of a method that requires no wafer bonding to produce CVD diamond on GaN/AlGaN using membranes2–4. In essence, GaN is grown on a Si substrate using metal organic chemical vapour deposition (MOCVD) and the Si substrate is selectively etched from the underside using a combination of photolithography and an inductively coupled plasma (ICP)4. This exposes very thin GaN/AlGaN membranes (<10 μm), suspended by a much thicker Si border which can be used to handle the sample. These fragile membranes can then be subjected to MPCVD for heteroepitaxial growth of thick polycrystalline diamond films (>20 μm). Using this approach, we demonstrate successfully adhered CVD diamond to the underside of the GaN/AlGaN.
In this work, we will present the fabrication process of CVD diamond on GaN membranes and the significant findings associated with this method4, not least the demonstration that these fragile structures survive the high induced thermal stresses during the CVD process2 and the significant improvement in the measured thermal boundary resistance between a Diamond/AlGaN interface and a Diamond/SiC/AlGaN interface3. Additionally, we will present the challenges and limitations of this methodology, including membrane bow from thermal stress, the etching artefacts from using a Si border and the limitations on membrane size and shape.
1 S. Mandal, E.L.H. Thomas, C. Middleton, L. Gines, J.T. Griffiths, M.J. Kappers, R.A. Oliver, D.J. Wallis, L.E. Goff, S.A. Lynch, M. Kuball, and O.A. Williams, ACS Omega 2, 7275 (2017).
2 J.A. Cuenca, M.D. Smith, D.E. Field, F. C-P. Massabuau, S. Mandal, J. Pomeroy, D.J. Wallis, R.A. Oliver, I. Thayne, M. Kuball, and O.A. Williams, Carbon 174, 647 (2021).
3 D.E. Field, J.A. Cuenca, M.D. Smith, S.M. Fairclough, F.C.-P. Massabuau, J.W. Pomeroy, O.A. Williams, R.A. Oliver, I. Thayne, and M. Kuball, ACS Appl. Mater. Interfaces 1 (2020).
4 M.D. Smith, J.A. Cuenca, D.E. Field, Y. Fu, C. Yuan, F. Massabuau, S. Mandal, J.W. Pomeroy, R.A. Oliver, M.J. Uren, K. Elgaid, O.A. Williams, I. Thayne, and M. Kuball, AIP Adv. 10, 035306 (2020).