Quantum oscillations in diamond field-effect transistors with a h -BN gate dielectric

Abstract

Shubnikov-de Haas (SdH) oscillations are a representative quantum transport phenomenon that is caused by Landau quantization of electronic states under applied magnetic field. 1 The frequency of the oscillation corresponds to the extremal cross-sectional area of the Fermi surface perpendicular to the magnetic field, while the temperature and magnetic-field dependences of the oscillation allow one to estimate the effective mass and lifetime of the charge carriers. The Berry phase associated with the cyclotron orbit and Landé g-factor can also be estimated. Thus, SdH oscillations are a powerful probe for investigating the fundamental properties of electronic states. One of the systems in which SdH oscillations have been intensively studied is the two-dimensional electron and hole gas in semiconductor field effect transistors (FETs); the semiconductors include emerging two-dimensional materials like graphene 2 , transition metal dichalcogenides 3 and black phosphorus 4 , as well as conventional Si 5,6 , Ge 7 , GaAs 8,9 and wide-band-gap GaN 10 and ZnO 11 . Diamond, with the same crystal structure as Si and Ge, is a promising future semiconductor material due to its excellent properties such as wide band-gap, high breakdown electric field, high thermal conductivity, and high intrinsic mobilities 12 . These properties are all superior to those of Si and Ge 13 . There have been extensive studies on diamond FETs 14-24 aimed at developing applications for high-power and high-frequency electronics. SdH oscillations in diamond, however, have been difficult to observe because of the low mobilities of the charge carriers in FET structures and have been reported only in our previous paper 25 .In that work, the SdH oscillations were observed in ionic-liquid-gated diamond FETs. Although the SdH oscillations provided evidence of the two-dimensional character of the hole gas that accumulates at the diamond surface, no clear dependence of the oscillations on gate voltage was observed, and the indicated spatial inhomogeneity of the hole gas remained an issue to be resolved.In this study, we create high-mobility two-dimensional hole gas in diamond using monocrystalline hexagonal boron nitride (h-BN) as a gate dielectric of diamond FETs (Figs. 1a and 1b). SdH oscillations are detected in both longitudinal (ρ xx ) and Hall (ρ yx ) resistivities with their frequencies clearly dependent on the gate voltage. The oscillations, as well as the background magnetic field dependence of ρ xx and ρ yx , are quantitatively explained by the standard theory of SdH oscillations. This result, combined with the suggested homogeneity of the electronic system, indicates the high quality of the hole gas. The estimated quantum lifetime also provides useful insights into the carrier scattering, which 2 6000 5000 4000 3000 2000 ρ xx (Ω) 16 12 8 4 0 B (T) V GS = −6 V −10 V −9 V −8 V

Charge-carrier mobility in hydrogen-terminated diamond field-effect transistors

“…The above comparison between the experimental and calculated mobility indicates that the surface impurity scattering is the dominant mechanism that limits the mobility of our FETs. This is consistent with our recent finding that the quantum and transport lifetime, which are estimated from Shubnikov-de Hass oscillations at low temperatures, are nearly the same 17 . The surface charged impurities may be adsorbed when the diamond surface is exposed to air before it is laminated by a flake of h-BN 10 .…”

Structural and electronic properties of 2D (graphene, hBN)/H-terminated diamond (100) heterostructures

“…Recent studies suggest using a thin layer of 2D materials as the gate dielectric layer to mitigate the limitations of oxide-based acceptor layers. 14,18 These studies report improvements in device parameters such as 2DHG channel carrier densities and mobilities. Motivated by these experiments, recent theoretical modeling based on the effective mass approach predicted that a thin layer of 2D layer as an interfacial capping layer can minimize the impact of interface roughness or even facilitate the charge transfer across the H-diamond/acceptor layer interface and improve the sheet hole concentration.…”

“…This spatial separation of electrons and holes by more than 5 Å in hBN/D(100) is highly desirable for minimizing the Coulomb scattering in the channel of SD-based diamond transistors. 18 In the semi-metallic nature of the G/D(100) system, there are no gap states originating from the graphene layer in the H-diamond (100) gap. As a result, the Fermi level pinning is minimal, and the graphene layer is expected to act as a metal contact.…”

A reactive molecular dynamics study of the hydrogenation of diamond surfaces

“…This is the most sought-after phase for quantum applications. In spite of its' applicability in the quantum as well as RF applications [3,33], this phase is the least understood phase in terms of its reconstruction mechanism [7]. At room temperature, we did not observe any structural reconstruction found in (100) phase, but the surface exhibited a quasiplanar configuration.…”