C-Si interface on SiO2/(111) diamond p-MOSFETs with high mobility and excellent normally-off operation

[Display omitted] •A high channel hole mobility of 200 cm2V−1s−1 was achieved in C-Si interface (111) diamond MOSFETs.•The C-Si interface provides the MOSFETs with an excellent normally-off operation.•The advantage of boron doping in (111) diamond provides a large maximum current density.•The anatomically flat and strain-free interface between the (111) diamond and SiO2 film was confirmed by HRTEM.•The existence of C-Si bonds at the interface was proved by EELS and XPS. In this paper, a diamond-silicon (C-Si) interface was constructed on a (111) 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 (Vth) of −16 V and a high current density of −167 mA/mm, with a gate length (LG) of 4 μm. The channel hole mobility (μFE) reaches 200 cm2V−1s−1 with a LG of 10 μm, and the interface state density (Dit) 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 (111) diamond, which ensures a high μFE and low Dit 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.