Large V_TH of Normally-OFF Field Effect Transistor With Yttrium Gate Material Directly Deposited on Hydrogen-Terminated Diamond

A normally- OFF field effect transistor (FET) with 20-nm yttrium (Y) gate material directly deposited on hydrogen-terminated (H-terminated) diamond surface has been successfully fabricated and characterized. The threshold voltage’s absolute value ( $\vert {V}_{TH}\vert $ ) varies from 1.62 to 2.12 V with the variation of different gate lengths ( ${L}_{G}$ ), which demonstrates an obviously normally- OFF characteristic. The large $\vert {V}_{TH}\vert $ could be greatly attributed to the fixed positive charge in the Al ₂ O ₃ layer and the large work function difference between Y and H-terminated diamond. The maximum drain–source current density ( ${I}_{Dmax}$ ) is −6.26 mA/mm. In addition, their Schottky barrier height is evaluated to be 0.71 eV. The large $\vert {V}_{TH}\vert $ could avoid the device failure from gate voltage overdrive. The technique exhibits the merits of uncontaminated interface in gate material and simple fabrication process, which is meaningful to the development of normally- OFF H-terminated diamond FET.