Abstract
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 Vth is relatively high at Vth = − 3.5 V, i.e., the positive charge model can reproduce the normally-off operation. Moreover, we also demonstrate that the Vth and transconductance gm correspond to those of the experimental work.
Highlights
Diamond is the most valuable p-type wide bandgap seimiconductor, thanks to its distinctive properties compared with other semiconductor materials, e.g., silicon carbide (SiC), germanium (Ge), and gallium nitride (GaN)
The fundamental operation mechanism of this structure is that the SiO2 considered as a source of positive charge, prevents the holes from accumulating near the interface by the cancellation of negative charge at the interface, i.e., achieving normally-off operation by shifting Vth to negative value
The breakdown voltage was achieved in the Al2O3/SiO2 diamond MOSFET device with the gate-drain distance LGD= 20 μm at 1275 V (Fig. 1f)
Summary
Diamond is the most valuable p-type wide bandgap seimiconductor, thanks to its distinctive properties compared with other semiconductor materials, e.g., silicon carbide (SiC), germanium (Ge), and gallium nitride (GaN). In the case of MOSFETs, the hydrogen termination can effectively induce the conductivity channel with the interface charge (fixed charge) in the electronic device surface This characteristic makes C–H diamond with p-channel conduction an emerging research topic, which develops feasible high power/high-frequency devices, including high-power FET for different applications, e.g., the inverter s ystems[4]. When nitrogent concentration is higher than boron concentration, Nitrogen atoms as donor with an activation energy of 1.7 eV fix the Fermi level at the same energy This technique is used to obtain a largely negative value of Vth indicating the normally-off operation in the diamond MOSFET devices under specific conditions, e.g., fixed positive charge of SiO2 close to the surface and fixed Fermi level by deep donor level in the bulk
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