Integration of Oxidized Silicon- and Hydrogen- Terminated Diamond p-Channels for Normally-Off High-Voltage Diamond Power Devices

With a dense two-dimensional hole gas (2DHG) p-type conductive layer near the surface, hydrogen- terminated (C-H) diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) have shown typical normally-on operations and high breakdown voltages ( ${V}_{\text {BR}}$ ). Owing to the high MOS interface quality, the oxidized silicon-terminated (C-Si–O) diamond MOSFETs have featured excellent normally-off characteristics, such as high threshold voltage ( ${V}_{\text {TH}}$ ). However, the reported C-Si–O diamond MOSFETs were all exhibited an overlapping-gate structure, and therefore couldn’t withstand high voltages. In this work, we demonstrated a novel C-H diamond MOSFET structure with a partial C-Si–O channel to improve the voltage withstand capability of normally-off C-Si–O diamond MOSFETs. The C-H/C-Si–O/C-H channel structure was achieved by forming an entire C-Si–O channel first, and then selectively replacing the C-Si–O channel to the C-H channel by using a SiO2 mask. As a result, for the fabricated device with a C-Si–O channel length of $2~\mu $ m and a gate-to-drain distance ( ${L}_{\text {GD}}$ ) of $11~\mu $ m, ${V}_{\text {TH}} = -8.6$ V and OFF-state ${V}_{\text {BR}} = -1376$ V have been obtained. These competitive results reveal that the proposed device structure is promising in pushing the normally-off C-Si–O diamond MOSFETs into the high voltage applications.