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• H-diamond surfaces have considerable potential for the field of electronic devices by virtue of the capability to form a high density of 2DHG. • The mechanism for the formation of 2DHG on H-diamond surfaces has not been completely elucidated as yet. • We establish ingenious theoretical models and provide compelling theoretical insight into the surface transfer doping model. • An interface with negative charges can induce an upward band bending on the H-diamond side. The surface transfer doping model has been extensively adopted as a mechanism to account for the generation of hole accumulation layers below hydrogen-terminated diamond (H-diamond) surfaces. To achieve effective surface transfer doping, surface electron acceptor materials with high electron affinity (EA) are required to produce a high density of two-dimensional hole gas (2DHG) on the H-diamond subsurface. We have established ingenious theoretical models to demonstrate that even if these solid materials do not have a high EA value, they remain capable of absorbing electrons from the H-diamond surface by forming a negatively charged interface to act as a surface electron acceptor in the surface transfer doping model. Our calculations, particularly for the local density of states, provide compelling evidence that the effect of an interface with negative charges induces an upward band bending on the H-diamond side. Furthermore, the valence band maximum of the diamond atoms at the interface crosses the Fermi level, giving rise to strong surface transfer p-type doping. These results give a strong theoretical interpretation of the origin of 2DHG on H-diamond surfaces. The proposed guidelines contribute to further improvements in the performance of 2DHG H-diamond field effect transistors. [Display omitted] [ABSTRACT FROM AUTHOR]

Diamond has become a promising candidate for high-power devices based on its ultrawide bandgap and excellent thermoelectric properties, where an appropriate gate dielectric has been a bottleneck hindering the development of diamond devices. Herein, we have systematically investigated the structural arrangement and electronic properties of diamond/high-κ oxide (HfO2, ZrO2) heterojunctions by first-principles calculations with a SiO2interlayer. Charge analysis reveals that the C–Si bonding interface attracts a large amount of charge concentrated at the diamond interface, indicating the potential for the formation of a 2D hole gas (2DHG). The diamond/HfO2and diamond/ZrO2heterostructures exhibit similar “Type II” band alignments with VBOs of 2.47 and 2.21 eV, respectively, which is consistent with experimental predictions. The introduction of a SiO2dielectric layer into the diamond/SiO2/high-κ stacks exhibits the typical “Type I″ straddling band offsets (BOs). In addition, the wide bandgap SiO2interlayer keeps the valence band maximum (VBM) and conduction band minimum (CBM) in the stacks away from those of diamond, effectively confining the electrons and holes in MOS devices. This work exhibits the potential of SiO2/high-κ oxide gate dielectrics for diamond devices and provides theoretical insights into the rational design of high-quality gate dielectrics for diamond-based MOS device applications.

Density functional theory (DFT) is a powerful quantum mechanical computational tool to perform electronic structure calculations for materials. Few DFT methods can ensure accuracy and efficiency simultaneously. DFT + U+ Vis an alternative effective approach to overcome this drawback. However, the accuracy sensitively depends on the self-consistent estimation of the high-dimensional onsite and intersite Hubbard interaction Uand Vterms. We propose Bayesian optimization using a dropout (BOD) algorithm, one type of active learning method, to optimize Uand Vterms. The DFT + U+ Vwith U/Vobtained by BOD can produce improved electronic properties for diverse bulk materials of comparable quality to the hybrid functionals with lower computational cost compared to the linear response approach. Note that the band gaps calculated by BOD are somewhat different from that of hybrid functionals by simply applying the same U/Vparameters as in the case of surface slabs and interfaces, which suggests that the transferability of U/Vfrom the bulk models to slabs and interfaces is not as well as expected. BOD is extended to calculate the U/Vparameters for slabs and interfaces and reach similar results as bulk solids. Moreover, we find that the U/Vare reasonably transferable between surface slabs and interfaces with different thicknesses under various effects of quantum confinement, which contributes to fast access to the electronic properties of large-scale systems with higher accuracy.