High Performance Single Crystalline Diamond Normally-Off Field Effect Transistors

High performance normally-off hydrogen-terminated diamond (H-diamond) MOSFETs were fabricated on single crystalline diamond grown in our lab. The device with 2-μm gate length shows threshold voltage of -1.0 V, and a drain current of 51.6 mA/mm at V
_GS
= V
_DS
= -4.5 V and an on-resistance of 65.39 Ω·mm. The transconductance keeps increasing when V
_GS
shifts from VTH toward more negative direction, and reaches the record high value of 20 mS/mm at V
_GS
of -4.5 V, which benefitted from the almost constant mobility of the holes in the gate voltage range of -4 V <; V
_GS
<; -2 V. The critical device process to realize these low on-resistance normally-off MOSFETs consists of 2-min UV ozone treatment of the H-diamond surface and thermal oxidation of aluminum film in the air to form an alumina gate dielectric.