Evaluation of Radiation Hardness of Hydrogen‐Terminated Diamond Metal‐Oxide‐Semiconductor Field‐Effect Transistors With Ion‐Implanted Buried p + Electrodes

Hydrogen‐terminated diamond metal‐oxide‐semiconductor field‐effect transistors with buried p + electrodes were fabricated using boron ion implantation. More than 50 devices on the same substrate were irradiated with X‐rays, and the changes in transistor characteristics were statistically analyzed up to a total dose of 10 MGy. The maximum drain current density, I D_MAX , increased from −24.58 to −32.08 mA/mm between the start of irradiation and a total dose of 3 MGy. This is attributed to oxygen vacancy trap states in the Al 2 O 3 gate oxide being gradually filled, which increased the negative fixed charge density and raised the hole density in the channel. After that, I D_MAX decreased to −27.16 mA/mm at a total dose of 10 MGy. This suggests that some structural change occurred in the Al 2 O 3 , which reduced the hole density—either by changing the amount of trapped electrons or by increasing interface trap states at the Al 2 O 3 /diamond interface. Also, threshold voltage shifts were used to quantitatively evaluate changes in the charge density inside the Al 2 O 3 . In addition, measurements using circular transmission line model showed that both the sheet resistance of the buried p + region and the specific contact resistance at the metal/p + interface remained nearly stable up to 10 MGy.