An enhanced two-dimensional hole gas (2DHG) C-H diamond with positive surface charge model for advanced normally-off...

Though the complementary power field effect transistors (FETs), e.g., metal-oxide-semiconductor-FETs (MOSFETs) based on wide bandgap materials, enable low switching losses and on-resistance, p-channel FETs are not feasible in any wide bandgap material other than diamond. In this paper, we propose the first work to investigate the impact of fixed positive surface charge density on achieving normally-off and controlling threshold voltage operation obtained on p-channel two-dimensional hole gas (2DHG) hydrogen-terminated (C-H) diamond FET using nitrogen doping in the diamond substrate. In general, a p-channel diamond MOSFET demonstrates the normally-on operation, but the normally-off operation is also a critical requirement of the feasible electronic power devices in terms of safety operation. The characteristics of the C-H diamond MOSFET have been analyzed with the two demonstrated charge sheet models using the two-dimensional Silvaco Atlas TCAD. It shows that the fixed-Fermi level in the bulk diamond is 1.7 eV (donor level) from the conduction band minimum.  However, the upward band bending has been obtained at Al₂O₃/SiO₂/C-H diamond interface indicating the presence of inversion layer without gate voltage. The fixed negative charge model exhibits a strong inversion layer for normally-on FET operation, while the fixed positive charge model shows a weak inversion for normally-off operation.  The maximum current density of a fixed positive interface charge model of the Al₂O₃/C-H diamond device is - 290 mA/mm, which corresponds to that of expermental result of Al₂O₃/SiO₂/C-H diamond - 305 mA/mm at a gate-source voltage of - 40 V. Also, the threshold voltage V_th is relatively high at V_th = - 3.5 V, i.e., the positive charge model can reproduce the normally-off operation. Moreover, we also demonstrate that the V_th and transconductance g_m  correspond to those of the experimental work.