Normally-Off Oxidized Si-Terminated (111) Diamond MOSFETs via ALD-Al₂O₃Gate 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 SiO2 masks with an atomic layer deposition (ALD)-Al2O3 film as the main gate insulator was proposed for the first time. Compositional analysis across the SiO2 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 SiO2 mask, a carbon-rich film was formed on SiO2 and C-Si bonding was realized at the SiO2/(111) diamond interface. The fabricated device with a source and drain distance (LSD) of 3μm exhibits a distinct threshold voltage (VTH) of -5.6 V and a maximum drain current density (IDMAX) 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-Al2O3 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.