Enhanced interface properties of diamond MOSFETs with Al2O3 gate dielectric deposited via ALD at a high temperature* *Project supported by the National Natural Science Foundation of China (Grant No. 61922021), the National Key Research and Development Project, China (Grant No. 2018YFE0115500), and the Fund from the Sichuan Provincial Engineering Research Center for Broadband Microwave Circuit High Density Integration, China.

Abstract

The interface state of hydrogen-terminated (C–H) diamond metal–oxide–semiconductor field-effect transistor (MOSFET) is critical for device performance. In this paper, we investigate the fixed charges and interface trap states in C–H diamond MOSFETs by using different gate dielectric processes. The devices use Al2O3 as gate dielectrics that are deposited via atomic layer deposition (ALD) at 80 °C and 300 °C, respectively, and their C–V and I–V characteristics are comparatively investigated. Mott–Schottky plots (1/C 2–V G) suggest that positive and negative fixed charges with low density of about 1011 cm−2 are located in the 80-°C- and 300-°C deposition Al2O3 films, respectively. The analyses of direct current (DC)/pulsed I–V and frequency-dependent conductance show that the shallow interface traps (0.46 eV–0.52 eV and 0.53 eV–0.56 eV above the valence band of diamond for the 80-°C and 300-°C deposition conditions, respectively) with distinct density (7.8 × 1013 eV−1⋅cm−2–8.5 × 1013 eV−1⋅cm−2 and 2.2 × 1013 eV−1⋅cm−2–5.1 × 1013 eV−1⋅cm−2 for the 80-°C- and 300-°C-deposition conditions, respectively) are present at the Al2O3/C–H diamond interface. Dynamic pulsed I–V and capacitance dispersion results indicate that the ALD Al2O3 technique with 300-°C deposition temperature has higher stability for C–H diamond MOSFETs.