Normally Off Hydrogen-Terminated Diamond Field-Effect Transistor With Ti/TiOx Gate Materials

A normally OFF hydrogen-terminated diamond (H-terminated diamond) field-effect transistor (FET) has been successfully achieved with Ti/TiO
_x
gate materials. A 5-nm Ti film was deposited on H-terminated diamond by electron beam evaporation technique and then it was thermally oxidized in air at 120 °C for 10 h to form Ti/TiO
_x
, which was confirmed by X-ray photoelectron spectroscopy. The threshold voltage of H-terminated diamond FET is −0.14 V at
${V}_{DS}$
of −8 V, indicating a normally OFF operation. The normally OFF property could be attributed to the difference of work difference between Ti and H-terminated diamond, which may deplete the hole carriers in H-terminated diamond 2-D hole gas (2DHG) conduction channel. The maximum mobility of H-terminated diamond FET is 313 cm
²
/Vs at
${V}_{GS}$
of −0.2 V. And, the fixed negative charge density is
$3.37 \times 10 _{11}$
cm
⁻²
. The results demonstrate that Ti/TiO
_x
H-terminated diamond FET is a good solution to fabricate normally OFF device with a simple fabrication process, undamaged 2DHG channel, and uncontaminated interface between Ti and TiO
_x
gate materials, which may promote the development of normally OFF H-terminated diamond FET.