C-Si interface on SiO₂/(1 1 1) diamond p-MOSFETs with high mobility and excellent normally-off operation

In this paper, a diamond-silicon (C-Si) interface was constructed on a (1 1 1) diamond substrate by annealing the SiO₂ gate insulator in a reductive atmosphere. Corresponding metal-oxide-semiconductor field effect transistors (MOSFETs) with a C-Si conductive channel were fabricated. The MOSFETs demonstrate excellent normally-off operation with a high threshold voltage (V_th) of −16 V and a high current density of −167 mA/mm, with a gate length (L_G) of 4 μm. The channel hole mobility (μ_FE) reaches 200 cm²V⁻¹s⁻¹ with a L_G of 10 μm, and the interface state density (D_it) is as low as 3.8 × 10¹¹ cm⁻² eV⁻¹. The high-resolution transmission electron microscopy (HRTEM) image displays a coherent and strain-free interface between the SiO₂ film and (1 1 1) diamond, which ensures a high μ_FE and low D_it in the MOSFETs. The interface is dominated by C-Si bonds, which are confirmed by atomic-scale electron energy loss (EELS) quantification, spectroscopic characterization, and X-ray photoelectron spectroscopy (XPS). These results demonstrate that diamond, directly combined with SiO₂, is ideal for implementation in power devices.