Effects of Regrown Layer Thickness and Nitrogen Concentration on Current Rise at Low Drain Voltage in Vertical Diamond MOSFET

Diamond is a promising material for power devices due to its excellent physical properties, and vertical p-channel field effect transistors (FETs) are important for realizing next-generation complementary inverters. In this study, we fabricated a (001) vertical diamond MOSFET using a 2-D hole gas (2DHG) induced by hydrogen-terminated diamond surfaces. The device incorporated a trench structure with a $1.5~\boldsymbol {\mu } $ m over-etch depth into the boron-doped diamond (p+) substrate. However, a suppressed drain current rise was observed in the low-voltage region (−4 V $\boldsymbol {\le } {V}_{\text {DS}}~\boldsymbol {\le }0$ V). To investigate the cause, we measured trench-type lateral devices in which the current does not pass through the regrown layer and increases rapidly in the low-voltage region. These results indicate that the regrown layer at the bottom of the trench is the dominant factor suppressing the drain current rise. Device simulations were performed with a fixed trench over-etch depth of $1.5~\boldsymbol {\mu } $ m while varying the thickness and nitrogen concentration of the regrown layer. The results showed that increasing either parameter raises the potential barrier for holes to penetrate the regrown layer, thereby suppressing the current rise. Reducing the nitrogen concentration and thinning the regrown layer improved the current rise. These findings offer valuable insights into improving the performance of vertical diamond FETs and support their application in future complementary power inverters.