Normally Off Hydrogen-Terminated Diamond Field-Effect Transistor With Ti/TiO<sub>x</sub> Gate Materials
Minghui Zhang, Wei Wang, Genqiang Chen, Haris Naeem Abbasi, Yanfeng Wang, Fang Lin, Feng Wen, Kaiyue Wang, Jingwen Zhang, Renan Bu, Hongxing Wang
Abstract
A normally OFF hydrogen-terminated diamond (H-terminated diamond) field-effect transistor (FET) has been successfully achieved with Ti/TiO<sub><i>x</i></sub> 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<sub><i>x</i></sub>, which was confirmed by X-ray photoelectron spectroscopy. The threshold voltage of H-terminated diamond FET is −0.14 V at <inline-formula> <tex-math notation="LaTeX">${V}_{DS}$ </tex-math></inline-formula> 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<sup>2</sup>/Vs at <inline-formula> <tex-math notation="LaTeX">${V}_{GS}$ </tex-math></inline-formula> of −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<sup>−2</sup>. The results demonstrate that Ti/TiO<sub><i>x</i></sub> 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<sub><i>x</i></sub> gate materials, which may promote the development of normally OFF H-terminated diamond FET.