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 _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 _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 SiO ₂ mask. As a result, for the fabricated device with a C–Si–O channel length of 2 μm and a gate-to-drain distance ( L _GD ) of 11 μm, V _TH = -8.6 V and OFF-state V _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.