Semiconductor technology World's first n-channel Diamond FET

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An American research team has developed the world's first n-channel diamond MOSFET. This is an important step towards integrated CMOS circuits for applications in harsh environments and the development of power electronic components from diamond.

The semiconductor diamond has interesting physical properties such as an extremely wide band gap of 5.5 eV, high charge carrier mobility, and high thermal conductivity. This makes this semiconductor promising for applications under extreme environmental conditions with high power and reliability, for example in environments with high temperatures and strong radiation (such as near nuclear reactor cores).

Diamond electronics not only reduce the need for cooling. These components also operate more energy-efficiently and can withstand significantly higher breakdown voltages.

In addition, diamond semiconductors are also capable of functioning under high temperature and strong radiation conditions in areas such as power electronics, spintronics, and MEMS sensing. The demand for peripheral circuits based on diamond CMOS components for monolithic integration has already increased.

Integrated CMOS circuits require both p-channel and n-channel MOSFETs, as are required for conventional silicon electronics. However, n-channel MOSFETs made from diamond had not yet been developed.

Breedng of n-type diamond semiconductors

A research team at the National Institute for Materials Science (NIMS) has now developed a special manufacturing process that can grow high-quality single-crystalline n-type diamond semiconductors, by doping homoepitaxial diamond layers of the (111) plane with a low concentration of phosphorus (image, diagram on the left).

The n-type (111) diamond epitaxy was grown with a step-flow nucleation mode, which allows precise control of crystal quality and donor distribution.

Thus, the team was the first in the world to create an n-channel MOSFET from diamond.

The phosphorus-doped epitaxial layers were created using microwave plasma-assisted chemical vapor deposition (MPCVD) on a type-Ib (111) high-pressure high-temperature diamond substrate (HPHT) with a misorientation of 3°.

The n-type diamond contains two phosphor-doped epilayers: a lightly doped diamond epilayer for the component channel and a heavily doped diamond epilayer for the ohmic contact (image, middle graphic).

The lightly doped n-diamond epitaxial layer was grown directly on the HPHT diamond substrate.

By using the latter diamond layer, the source and drain contact resistance was significantly reduced. The team confirmed that the manufactured diamond MOSFET indeed functioned as an n-channel transistor.

In addition, the team demonstrated the excellent high-temperature performance of the MOSFET, which results from the field-effect mobility of about 150 cm²/V・s at 300 °C (Image, graph on the right).

These achievements should facilitate the development of integrated CMOS circuits for the production of energy-efficient power electronics, spintronic components, and (MEMS) sensors under harsh conditions.

The project was conducted by Meiyong Liao from the Research Center for Electronic and Optical Materials (RCEOM, NIMS), Huanying Sun (RCEOM, NIMS), and Satoshi Koizumi (RCEOM, NIMS). The project was described in 'Advanced Science' (doi.org/10.1002/advs.202306013). (kr)

*Henning Wriedt is a freelance technical author.