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

Abstract

A normally OFF hydrogen-terminated diamond (H-terminated diamond) field-effect transistor (FET) has been successfully achieved with Ti/TiO_<i>x</i> 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 &#x00B0;C for 10 h to form Ti/TiO_<i>x</i>, which was confirmed by X-ray photoelectron spectroscopy. The threshold voltage of H-terminated diamond FET is &#x2212;0.14 V at <inline-formula> <tex-math notation="LaTeX">${V}_{DS}$ </tex-math></inline-formula> of &#x2212;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 cm²/Vs at <inline-formula> <tex-math notation="LaTeX">${V}_{GS}$ </tex-math></inline-formula> of &#x2212;0.2 V. And, the fixed negative charge density is <inline-formula> <tex-math notation="LaTeX">$3.37 \times 10 _{11}$ </tex-math></inline-formula> cm^&#x2212;2. The results demonstrate that Ti/TiO_<i>x</i> 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_<i>x</i> gate materials, which may promote the development of normally OFF H-terminated diamond FET.