Normally-Off High-Performance Diamond FET With Large VTH and Low Leakage Current

A normally-off high-performance hydrogenated diamond (H-diamond) field-effect transistor (FET) has been fabricated and investigated. The deep X-ray photoelectron spectroscopy (XPS) analysis reveals the Gd2O3/Gd double layer gate structure. The threshold voltage ( ${V}_{\text {TH}}$ ) is up to −1.4 V with 6- $\mu $ m gate length, which demonstrates the normally-off operation caused by the low work function of Gd and the fixed positive charge of Gd2O3 layer. The gate leakage current density J is as low as $5.8\times 10^{-{6}}$ A/cm2 and ON/OFF ratio is as high as $10^{{10}}$ , which both can be due to the suppression by Gd2O3 layer. The maximum drain current density, transconductance, OFF-state drain leakage current, subthreshold swing, maximum gate oxide capacitance, and effective mobility with 6- $\mu $ m gate length are −100 mA/mm, 18.9 mS/mm, $10^{-{8}}$ mA/mm, 121 mV/dec, $0.24~\mu $ F/cm2, and 417.7 cm2/V $\cdot $ s, respectively. The trapped charge density, fixed charge density, and interface state density are $4.87\times 10^{{11}}$ cm $^{-{2}}$ , $3.57\times 10^{{12}}$ cm $^{-{2}}$ , and $1.52\times 10^{{12}}$ cm $^{-{2}}\cdot $ eV $^{-{1}}$ , respectively. This work demonstrates a simple fabrication approach to achieve normally-off FET with large ${V}_{\text {TH}}$ and low leakage current, which contributes to the advancement of diamond for circuit applications.