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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.

The exceptional electronic properties of cadmium telluride (CdTe) allow the material to be used in a wide range of high energy radiation detection applications. Understanding the mechanisms of local carrier scattering is of fundamental importance to understand the charge transport in the material. Here, we investigate the effect of photoexcitation on electron transport properties in chlorine doped single crystalline cadmium telluride (SC-CdTe:Cl). For this purpose time of flight measurements were performed on SC-CdTe:Cl in order to study the electron drift mobility in the low injection regime. Measurements were made at the temperature intervals of 80 to 300 K, for an applied electric field between 270 and 1600 V/cm and for wavelengths of 532, 355 and 213 nm. We have found that the electron drift mobility was affected by the excitation energy for temperatures below 200 K. In addition, the measurements revealed that it is possible to determine impurity and shallow trap concentration by this method. The method proves to be extremely sensitive in measuring very low impurity levels and in identifying dominant scattering mechanisms. 

A method based on the scaling properties of the Boltzmann transport equation is proposed to identify the dominant scattering mechanisms that affect charge transport in a semiconductor. This method uses drift velocity data of mobile charges at different lattice temperatures and applied electric fields and takes into account the effect of carrier heating. By performing time‐of‐flight measurements on single‐crystalline diamond, hole and electron drift velocities are measured under low‐injection conditions within the temperature range 10–300 K. Evaluation of the data using the proposed method identifies acoustic phonon scattering as the dominant scattering mechanism across the measured temperature range. The exception is electrons at 100–200 K where conduction‐band valley repopulation has a prominent effect. At temperatures below ≈80 K, where valley polarization is observed for electrons, transport dominated by acoustic phonon scattering is observed in different valleys separately. The scaling model is additionally tested on data from highly resistive gallium arsenide samples to demonstrate the versatility of the method. In this case, impurity scattering can be ruled out as the dominant scattering mechanism in the samples for the temperature range 80–120 K.

The mobility-lifetime (μτ) product is an important parameter that determines the performance of electronic and photonic devices. To overcome the previously reported difficulties in measuring the μτ product at cryogenic temperatures, we implement a time-resolved cyclotron resonance method to determine the carrier lifetime τ. After clarifying the difference between the AC and DC mobilities measured by cyclotron resonance and time-of-flight methods, respectively, we demonstrate an inverse temperature dependence of the μτ product. The highest recorded μτ product of 0.2 cm²/V, which is approximately 100 times the room-temperature value, was obtained at 2 K for chemical-vapor-deposition diamond of the highest currently available purity.

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.

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.

Although theoretical investigations indicate that the successful combination of graphene and diamond would give interesting properties, only a limited number of reports dealing with the subject have been published. Here, we present a rapid thermal process (RTP) which involves nickel (Ni) as metal catalyst for a direct growth of graphene on diamond at a temperature of 1073 K for 60 s. This process operates with a combination of a lower temperature and for a shorter duration than what has previously been reported. Thin Ni films of different thicknesses were deposited on top of (100) single-crystalline diamond. After RTP, the coverage of monolayer graphene was found to be around 20% shown by the intensity ratio between the 2D- and G-peak using Raman spectroscopy on 50 nm thick Ni films. In addition, x-ray photoelectron spectroscopy and atomic force microscopy analysis were conducted. For electrical characterization, Hall-effect measurements were performed at temperatures between 80 and 360 K.

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.