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A mobility-enhanced normally off hydrogen-terminated diamond (H-diamond) field-effect transistor (FET) with low interface state density has been realized using Al2O3/Nd gate stack deposited by electron beam evaporator. The threshold voltage is extracted to be −1.48 V, indicating an obvious normally off characteristic. The enhancement mode could be ascribed to the large work function difference between Nd and H-diamond. The subthreshold swing is deduced as low as 86.3 mV/dec, revealing a high working speed in the subthreshold region. More importantly, the mobility (518.5 cm2/V·s) has been enhanced due to the fairly low interface state density (3.19 × 1011 cm−2·eV−1). In addition, the device exhibits a relatively low trapped charge density and fixed charge density from the C–V characteristic. This work provides a simple method to realize the normally off device and suggests the great potential of adopting the Al2O3/Nd gate stack for achieving high-performance H-diamond FET. [ABSTRACT FROM AUTHOR]

A normally off hydrogen-terminated diamond (H-diamond) metal-oxide-semiconductor field effect transistor (MOSFET) is realized by using lanthanum oxide (La2O3) gate dielectric. The threshold voltage is demonstrated to be −0.797 V, indicating that the La2O3-gated H-diamond MOSFET has normally off characteristics. The normally off mode could be greatly ascribed to the low work function of La2O3. Based on the capacitance–voltage (C–V) curves, the dielectric constant of La2O3 is calculated to be as high as 25.6. Moreover, the small hysteresis voltage extracted from the C–V curves exhibits low trapped charge density in the La2O3 layer. The maximum drain–source current, maximum transconductance, subthreshold swing, effective mobility, current on/off ratio, and sheet hole density of La2O3-gated MOSFET with a gate length of 2 μm are calculated to be −13.55 mA/mm, 4.37 mS/mm, 161 mV/dec, 202.2 cm2/V·s, 108, and 6.53 × 1012 cm−2, respectively. This work will significantly promote the development of normally off H-diamond MOSFET devices. [ABSTRACT FROM AUTHOR]