Design and construction of a large-area hot filament reactor suitable for deposition of diamond films directly onto GaN substrates

Lead Research Organisation: University of Bristol
Department Name: Chemistry

Abstract

This PhD is aligned with the Program grant (PI Martin Kuball, Physics) with the aim of developing diamond-on-GaN technology for next generation power devices. It is funded by the University of Bristol's EPSRC DTA quota as part of their commitment to support the overall Programme grant.
The student will work alongside a PDRA (whose remit is to develop new technologies to grow diamond directly on to GaN substrates), and develop methods and procedures to scale up this technology from substrates that are ~1sq.cm in size to 6"-diameter wafers common in the semiconductor industry. The student's main goal will be to modify an existing deposition reactor such that it can accept 6"-wafers, and to redesign the filament and power system such that diamond films will be deposited uniformly across these wafers.
Some of the project will also involve scaling up of the seeding process, which currently uses a home-built electrospray apparatus. This will also be modified for larger-area substrates. Some preliminary seeding a deposition experiments will be undertaken on a range of novel substrates and materials, such as black Si needles, to fully understand the operating parameters.
The student will be trained on various characterisation facilities, such as SEM, Raman, 4-point probe, as well as vacuum engineering.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509619/1 01/10/2016 30/09/2021
1942608 Studentship EP/N509619/1 18/09/2017 31/03/2021 Edmund Smith
 
Description Diamond growth on GaN substrates has been investigated, with delamination of the diamond layer after growth being unavoidable, given the thermal expansion mismatch of the materials.
However, some promising work has yielded from diamond growth onto AlN, which is a material that could form part of a GaN HEMT device. This work showed that using a mixed-size seeding prior to diamond growth grew diamond layers that did not delaminate and showed a good thermal conductivity - which is the primary reason for attempting to grow diamond onto GaN.
Simultaneously, the large area reactor has been built and initial testing has been good, with good quality growth onto 1" square substrates, but redesigns to allow for larger growth (up to 6" squares) are currently underway.
Exploitation Route Using the improved seeding method and growth procedure developed from this funding, construction of a GaN device cooled using a diamond heat spreader is much more viable. The next step of this would be to grow diamond layers onto AlN-on-GaN substrates, which would require further development into the processes used to make those substrates.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Electronics