Enhanced interface properties of diamond MOSFETs with Al₂O₃ gate dielectric deposited via ALD at a high temperature

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 Al_2O_3 as gate dielectrics that are deposited via atomic layer deposition (ALD) at 80 ^\circC and 300 ^\circC, respectively, and their C-V and I-V characteristics are comparatively investigated. Mott-Schottky plots (1/C^2-V_\rm G) suggest that positive and negative fixed charges with low density of about 10^11 cm^-2 are located in the 80-^\circC- and 300-^\circC deposition Al_2O_3 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-^\circC and 300-^\circC deposition conditions, respectively) with distinct density (7.8 \times 10^13 eV^-1\cdotcm^-2-8.5 \times 10^13 eV^-1\cdotcm^-2 and 2.2 \times 10^13 eV^-1\cdotcm^-2-5.1 \times 10^13 eV^-1\cdotcm^-2 for the 80-^\circC- and 300-^\circC-deposition conditions, respectively) are present at the Al_2O_3/C-H diamond interface. Dynamic pulsed I-V and capacitance dispersion results indicate that the ALD Al_2O_3 technique with 300-^\circC deposition temperature has higher stability for C-H diamond MOSFETs.