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The integration of single-layer graphene with diamond substrates offers a promising platform for highperformance electronic devices by utilizing the exceptional properties of both materials. This study describes a fabrication process and transport measurements of single-layer graphene devices on diamond substrates featuring two surface terminations: hydrogen (H-terminated, thermal process) and oxygen (O-terminated, plasma treatment). The carrier transport properties were investigated using Hall effect measurements over a broad temperature range (80-400 K) under high-vacuum conditions (1 x 10^-4 mbar). Our findings reveal that thermal annealing significantly improves the graphene-diamond interface quality, causing a notable increase in carrier mobility for devices on both H- and O-terminated from 1439 to 1644 cm²/Vs and from 1238 to 1340 cm²/Vs, respectively. We also found that the effect of remote interfacial phonon scattering on high-temperature mobility is affected by the termination type. These findings highlight the importance of substrate surface engineering and offer a pathway for optimizing graphene-diamond heterostructures for advanced electronic applications.

Understanding the electrically active defects and impurities in semiconductors, especially in intrinsic or unintentionally doped wide bandgap materials, still remains a challenge. Here, time-of-flight (ToF) measurement using a solid state light source (355 and 213 nm) was performed on intrinsic silicon carbide and single-crystalline diamond. The charge transient spectroscopy (QTS) and the inverse Laplace (IL) QTS methods were applied to analyze the ToF results. Using these methods, we were able to trace the existing impurities in both materials. However, ILQTS proved to be more sensitive, with higher resolution for detection of existing multiple defects. The results suggest that this system can successfully be employed to investigate electrically active impurities at different energy states in highly resistive and undoped materials.

The high current-carrying capacity of graphene is essential for its use as an interconnect in electronic and spintronic circuits. At the same time, knowing the breakdown limits and mechanism under high fields can enable new device design strategies. In this work, we push the current carrying capacity of the scalable form of chemical vapor deposited (CVD) graphene employing a high-thermal conducting single crystalline diamond substrate. Our experiments on CVD graphene reveal extremely high current densities > 10⁹ A/cm² in graphene on the diamond with both ohmic (low-resistive) and tunneling tunnel (high-resistive) contacts. Measurements on ferromagnetic (TiO_x/Co) and metallic (Ti/Au) contacts demonstrate current densities of ∼1.16×10⁹ A/cm² and ∼1.7×10⁹ A/cm², respectively. The tunnel (high-resistive) contacts exhibit a shunting of graphene under high currents via the bottom graphitized diamond, resulting in dielectric breakdown and via alternative conducting paths. Electrical measurements show a distinct threshold for conducting paths of graphitized diamond, in tune accordance with Middleton-Wingreen's theory. Our results of high current densities achieved in CVD graphene, with distinct dependence on ohmic and tunneling, contact resistance, and the observed breakdown mechanism, provide new insights for enabling high-current all carbon circuits.

Graphene on diamond has emerged as a promising platform for various electronic applications. This brief review article explores the recent advancements and the potential of graphene on diamond for electronic applications with a focus on single-crystal (SC) chemically vapor-deposited and high-pressure and high-temperature diamond. Device fabrication techniques, properties, and performance of single-layer graphene on diamond in various electronic devices are discussed. This hybrid system's challenges and prospects are also analyzed. A particular emphasis is placed on the unique benefits of diamond as a substrate for graphene and its growth, including its high thermal conductivity, mechanical strength, high optical phonon energy, and the importance of achieving high-quality single-layer graphene on SC diamond.

The outstanding electronic properties of graphene make this material a candidate for many applications, for instance, ultra-fast transistors. However, self-heating and especially the detrimental influence of available supporting substrates have impeded progress in this field. In this study, we fabricate graphene-diamond heterostructures by transferring graphene to an ultra-pure single-crystalline diamond substrate. Hall-effect measurements were conducted at 80 to 300 K on graphene Hall bars to investigate the charge transport properties in these devices. Enhanced hole mobility of 2750 cm(2) V-1 s(-1) could be observed at room-temperature when using diamond with reduced nitrogen (N-s(0)) impurity concentration. In addition, by electrostatically varying the carrier concentration, an upper limit for mobility is determined in the devices. The results are promising for enabling carbon-carbon (C-C) devices for room-temperature applications.

Using the state of valley-polarization of electrons in solids is a promising new paradigm for information storage and processing. The central challenge in utilizing valley-polarization for this purpose is to develop methods for manipulating and reading out the final valley state. Here, we demonstrate optical detection of valley-polarized electrons in diamond. It is achieved by capturing images of electroluminescence from nitrogen-vacancy centers at the surface of a diamond sample that are excited by electrons drifting and diffusing through the sample. Monte Carlo simulations are performed to interpret the resulting experimental diffusion patterns. Our results give insight into the drift-diffusion of valley-polarized electrons in diamond and yield a way of analyzing the valley-polarization of ensembles of electrons.

The interaction between acoustic phonons and electrons in diamond has been investigated by comparing state-of-the-art time-of-flight drift velocity measurements with Monte Carlo simulations. We use a multivariable anisotropic description of acoustic deformation potential scattering. The phonon-electron interaction is the limiting factor for the carrier mobility in ultrapure single crystal diamond. Hence, having a correct description is necessary for both device simulations and for predicting the maximum device performance. The experiments were performed at low temperature and using ultrapure diamond to minimize the influence of other scattering sources. The electronic valley polarization in diamond at low temperatures enables determination of both uniaxial and dilatation deformation potentials in the same experiment. The uniaxial and dilatation deformation potentials are found to be 18.5±0.2 and −5.7±0.3 eV, respectively.

Transistors operating at high frequencies are the basic building blocks of millimeter-wave communication and sensor systems. The high charge-carrier mobility and saturation velocity in graphene can open way for ultra-fast field-effect transistors with a performance even better than what can be achieved with III-V-based semiconductors. However, the progress of high-speed graphene transistors has been hampered by fabrication issues, influence of adjacent materials, and self-heating effects. Here, we report on the improved performance of graphene field-effect transistors (GFETs) obtained by using a diamond substrate. An extrinsic maximum frequency of oscillation fmax of up to 54 GHz was obtained for a gate length of 500 nm. Furthermore, the high thermal conductivity of diamond provides an efficient heat-sink, and the relatively high optical phonon energy of diamond contributes to an increased charge-carrier saturation velocity in the graphene channel. Moreover, we show that GFETs on diamond exhibit excellent scaling behavior for different gate lengths. These results promise that the GFET-on-diamond technology has the potential of reaching sub-terahertz frequency performance.

Extending the limit of charge-carrier mobility in semiconductors has been a long-standing pursuit in material science and its applications. Herein, we investigate the electron mobility via cyclotron resonance in undoped diamond under continuous-wave photoexcitation, whereby the density of charge carriers can be reduced to 10⁸cm⁻³ or 1/10 of the previous detection limit [K. Konishi et al., Appl. Phys. Lett. 117, 212102 (2020)]. For low-density electrons, which obviate the effects of carrier-carrier scattering as a broadening mechanism, we observe an extraordinarily narrow cyclotron resonance spectrum. After correcting for the microwave power broadening, the highest intrinsic mobility value of 100×10⁶ cm²V⁻¹s⁻¹ is obtained at 3 K, which is a 16-fold increase of the mobility compared with the previous record in diamond. Our result is beneficial for the design and application of diamond radiation detectors implemented for their practical use at cryogenic temperatures.

The valley degree of freedom in many-valley semiconductors provides a new paradigm for storing and processing information in valleytronic and quantum-computing applications. Achieving practical devices requires all-electric control of long-lived valley-polarized states, without the use of strong external magnetic fields. Because of the extreme strength of the carbon–carbon bond, diamond possesses exceptionally stable valley states that provide a useful platform for valleytronic devices. Using ultrapure single-crystalline diamond, we demonstrate electrostatic control of valley currents in a dual-gate field-effect transistor, where the electrons are generated with a short ultraviolet pulse. The charge current and the valley current measured at the receiving electrodes are controlled separately by varying the gate voltages. We propose a model to interpret experimental data, based on drift-diffusion equations coupled through rate terms, with the rates computed by microscopic Monte Carlo simulations. As an application, we demonstrate valley-current charge-state modulation of nitrogen-vacancy centers.