Enhancement of drain soft-breakdown strength to 1.1 MV/cm for hydrogen-terminated diamond MOSFETs by mitigating hydrogen-induced defects

Diamond surface quality is critical to improve the power and reliability for the hydrogen-terminated diamond (H-diamond) metal-oxide-semiconductor field-effect transistors (MOSFETs). In this Letter, significant surface microdefects were identified in the H-diamond after heat treatment at less than 500 °C. These microdefects may be caused by thermal bubbling of free hydrogen introduced during the diamond hydrogenation process and are, therefore, referred to as hydrogen-induced defects in this paper. Based on the peak intensity of the grazing incidence x-ray diffraction spectra, the long-range ordering of the H-diamond surface lattice degrades with the heat treatment temperature. To explain the effect of these hydrogen-induced defects on the drain breakdown of H-diamond MOSFETs, a critical electric field model considering hydrogen bubbling effect is proposed. It indicates that mitigation of hydrogen-induced defects would improve the long-range ordering of H-diamond surface lattice and, thus, increase the H-diamond breakdown strength. Next, two kinds of Al2O3/H-diamond MOSFETs with the same device structure are fabricated by depositing Al2O3 at 150 and 450 °C, respectively. It is verified that the H-diamond MOSFET with Al2O3 deposited at 150 °C exhibits a drain soft-breakdown strength 4.75 times greater than that of the device with Al2O3 deposited at 450 °C. By mitigating the hydrogen-induced defects in the H-diamond surface, a record drain soft-breakdown strength of 1.1 MV/cm is reached for the Al2O3/H-diamond MOSFET. These results would be helpful in improving the power and reliability of H-diamond devices.