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 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. (paper)