Enhanced interface properties of diamond MOSFETs with Al_2O_3 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$_{2}$O$_{3}$ as gate dielectrics that are deposited via atomic layer deposition (ALD) at 80 $^\circ$C and 300 $^\circ$C, 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-$^\circ$C- and 300-$^\circ$C deposition Al$_{2}$O$_{3}$ 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-$^\circ$C and 300-$^\circ$C deposition conditions, respectively) with distinct density ($7.8 \times 10^{13}$ eV$^{-1}\cdot$cm$^{-2}$-$8.5 \times 10^{13}$ eV$^{-1}\cdot$cm$^{-2}$ and $2.2 \times 10^{13}$ eV$^{-1}\cdot$cm$^{-2}$-$5.1 \times 10^{13}$ eV$^{-1}\cdot$cm$^{-2}$ for the 80-$^\circ$C- and 300-$^\circ$C-deposition conditions, respectively) are present at the Al$_{2}$O$_{3}$/C-H diamond interface. Dynamic pulsed $I$-$V$ and capacitance dispersion results indicate that the ALD Al$_{2}$O$_{3}$ technique with 300-$^\circ$C deposition temperature has higher stability for C-H diamond MOSFETs.