A stable deep depletion regime is demonstrated in metal oxide semiconductor capacitors using p-type oxygen-terminated (100) diamond as a semiconductor and Al2O3 deposited by Atomic Layer Deposition at 380 °C. Current voltage I(V) and capacitance voltage C(V) measurements were performed to evaluate the effectiveness of diamond semiconductor gate control. An effective modulation of the space charge region width is obtained by the gate bias, where the deep depletion regime is demonstrated for a positive gate bias. The deep depletion concept is described and proposed for MOSFET devices. Finally, a proof of concept of diamond deep depletion MOSFETs is presented.

Diamond has been explored to develop prototype field-effect transistors (FETs). At present, various architectures that are suited to high temperature and high-radiation environments are still under investigation for power electronics applications. Recently, the deep-depletion diamond metal–oxide–semiconductor FET (D3MOSFET) concept has been introduced and demonstrated to be a good candidate for designing efficient diamond MOSFETs. In this paper, a general introduction to the concept of deep depletion is given. The key issues concerning the design and fabrication of this kind of diamond MOSFET are then described and discussed in terms of quasi static performance (the ‘on’ and ‘off’ states). A demonstration of the working regimes of a fabricated normally-on D3MOSFET is described, which reached a critical field of at least 5.4 MV cm−1 at a drain–source bias of −175 V, without electric field relaxation structures. The minimum on-state resistance was measured and found to be R ON,S  = 50 mΩ cm2 at 250 ∘C. Finally, the D3MOSFET is contextualized as part of a global research effort to develop diamond power FETs. Some of the main challenges regarding the fabrication of competitive D3MOSFETs and, more generally, diamond power devices are discussed.