Normally-Off Oxidized Si-Terminated (111) Diamond MOSFETs via ALD-Al2O3 Gate Insulator With Drain Current Density Over 300 mA/mm

A novel method to fabricate the oxidized silicon-terminated (C–Si–O) diamond metal-oxide-semi- conductor field-effect transistors (MOSFETs) by replacing the retained SiO
₂
masks with an atomic layer deposition (ALD)-Al
₂
O
₃
film as the main gate insulator was proposed for the first time. Compositional analysis across the SiO
₂
masks and on the air-exposed C–Si–O (111) diamond surface has been carried out by utilizing secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) techniques, respectively. Furthermore, we revealed that, under selectively epitaxial growth of diamond through a SiO
₂
mask, a carbon-rich film was formed on SiO
₂
and C–Si bonding was realized at the SiO
₂
/(111) diamond interface. The fabricated device with a source and drain distance (
${L}_{SD}$
) of
$3 \,\mu \text{m}$
exhibits a distinct threshold voltage (
${V}_{TH}$
) of −5.6 V and a maximum drain current density (
${I}_{D\_{}{MAX}}$
) up to −311 mA/mm, which is a record value among normally-off single-crystalline diamond MOSFETs to date. In the case of having ALD-Al
₂
O
₃
as the main gate insulator, normally-off operation of the C–Si–O diamond MOSFETs has a stark contrast with the typically normally-on performance of the hydrogen-terminated (C–H) diamond MOSFETs, which is mainly due to the smaller negative electron affinity of C–Si–O diamond compared with that of C–H diamond. These results indicate that the proposed C–Si–O (111) diamond MOSFETs with excellent normally-off operation and large drain current density are promising to fulfill the requirements of fail-safe and current drive capabilities in power device applications.