Diamond Microwave has substantial experience in the development of diamond as a semiconductor, and holds several patents related to diamond transistor structures.
Key findings from our diamond transistor R&D were published in the Journal of Applied Physics* detailing our work on boron delta-doped CVD diamond structures with surface delta layers <1nm thick. Hall-effect measurements indicated a substantial Hall mobility of up to 900 cm²/Vs, which would normally be indicative of material highly suitable for transistor action. However, we also showed that the established analysis of Hall data using a single homogeneously doped layer can result in a dramatic over-estimate of mobility. The conductivity mobility is the important measure for most device applications and despite the high measured values of Hall mobility, the room temperature conductivity mobility was shown to be much lower in the range 1 - 4 cm²/Vs. Field-effect mobility extracted from our diamond FET structures was also in close agreement with the conductivity mobility. This experimental work was consistent with our modeling which even for optimistic scenarios predicted a room temperature conductivity mobility of <40 cm²/Vs. Our work strongly indicates that to achieve high conductivity mobility in a boron doped surface delta structure on diamond and therefore achieve a practical diamond transistor, a high degree of carrier excitation is required from the lowest sub-band into 3D bulk states. The challenge is to achieve this at room temperature.
The company continues to carry out research into diamond transistor technology and is collaborating with the London Centre for Nanotechnology at University College London (UCL).
*Transport Behavior of Holes in Boron Delta-Doped Diamond Structures, R. S. Balmer, I. Friel, S. Hepplestone, J. Isberg, M. J. Uren, M. L. Markham, N. L. Palmer, J. Pilkington, P. Huggett, S. Majdi, and R. Lang, J. Appl. Phys., 113, (2013)