C-Si Interface on Sio2/(111) Diamond P-Mosfets with High Mobility and Excellent Normally-Off Operation

In this paper, a diamond-silicon (C-Si) interface was constructed on a (111) diamond substrate by annealing the SiO2 gate insulator in the reductive atmosphere. The corresponding metal-oxide-semiconductor field effect transistors (MOSFETs) with the C-Si conductive channel were fabricated. The C-Si diamond MOSFETs demonstrate excellent electrical performances, including a maximum current density of -167 mA/mm at the channel length (Lch) of 4 μm and the excellent normally-off operation with the large threshold voltage (Vth) of -14 V. Moreover, the MOSFETs also show a low interface state density (Dit) of 9.7×1011 cm-2 eV-1 and a high channel hole mobility (μFE) of 200 cm2V-1s-1 (at VDS=-15 V) with Lch=10 μm. The high-resolution transmission electron microscopy (HRTEM) image shows a coherent and strain-free interface between the (111) diamond and SiO2 film, which ensures the low Dit and high μFE of the MOSFETs. The interface dominated by C-Si bonds is confirmed by atomic-scale electron energy loss (EELS) quantification, spectroscopic characterization, and X-ray photoelectron spectroscopy (XPS). The coverage of C-Si bonds on (111) diamond surface provides considerable positive charges in the SiO2 layer, which ensures the excellent normally-off operation in the diamond p-MOSFETs.