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TiO 2 /Al 2 O 3 bi-layer gate dielectric-based H-terminated diamond MOSFET: Improved mobility by mitigation of remote Coulomb scattering
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DOI：10.1016/j.diamond.2026.114012.png)
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Abstract
En 中文
Hydrogen-terminated diamond field-effect transistors (FETs) are promising candidates for high-power and high-frequency electronics due to their high carrier mobility and exceptional thermal properties. However, carrier transport in these devices is often limited by Coulomb scattering originating from fixed charges in the gate dielectric. In this work, we demonstrate a thermally grown TiO 2 /Al 2 O 3 bilayer gate dielectric for H-terminated diamond MOSFETs that significantly improves channel transport. Devices with conventional Al 2 O 3 gate dielectrics are compared with transistors incorporating an additional TiO 2 overlayer while maintaining otherwise identical fabrication processes. The bilayer dielectric devices exhibit improved electrical characteristics, including an increase in peak transconductance from 2.0 to 2.4 mS/mm, a reduction in subthreshold swing from 104.1 mV/dec to 74.9 mV/dec, and a three-order reduction in gate leakage current. The saturation drain current increases from −5.2 mA/mm to −6.8 mA/mm, while the linear region resistance decreases from approximately 0.65 to 0.57 k Ω⋅mm . Capacitance–voltage measurements indicate that the two-dimensional hole gas (2DHG) density remains nearly unchanged for both dielectric stacks under similar gate bias conditions. This suggests that the performance enhancement arises primarily from improved carrier mobility rather than increased carrier density. We attribute the mobility improvement to mitigation of remote Coulomb scattering caused by fixed positive charges in Al 2 O 3 . The TiO 2 layer is proposed to introduce a dipolar charge distribution that partially screens these Coulomb potentials, thereby reducing the scattering of channel carriers. The results demonstrate that dielectric stack engineering provides an effective strategy for improving carrier transport in diamond MOSFETs without altering the channel formation mechanism.
Keywords:
Diamond FET
Remote Coulomb scattering
Bi-layer dielectric
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