We report the first observation of narrow-band 1.3 MeV γ radiation from a crystalline diamond microundulator. A diamond superlattice was grown with a periodically varying boron doping profile. Four sinusoidally deformed (110) periods resulted with a period length of 5.0 µm and an amplitude of 0.098 nm. A channeling experiment was performed with the 855 MeV electron beam of the Mainz Microtron MAMI accelerator facility. A clear peak was detected with a large sodium iodide scintillation detector close to the expected photon energy of 1.28 MeV. Key characteristics of the peak, including photon energy, width, and intensity, were reproduced fairly well by Monte Carlo simulation calculations. Based on the latter, optimized boron doping profiles were designed for a hypothetical 3 GeV electron beam, enabling preparation of a highly directional γ-ray beam with a photon energy of 14.5 MeV. The predicted spectral bandwidth is 13%, however, with a high-energy continuum tail. The on-target photon flux at a beam current of 100 µA would be about 10^{12}s^{−1}.

Diamond, with its exceptional electrical and thermal characteristics, is a promising wide bandgap material for high-performance electronics in extreme environments. However, the efficiency of diamond-based metal oxide semiconductor devices is often hindered by interface states between the diamond and the oxide layer, which can degrade mobility, threshold voltage, and gate control. Al2O3 is commonly used as the insulating layer due to its compatibility with diamond, but its interface with diamond can introduce undesirable states that affect device performance. This work focuses on the OH-terminated (111) diamond/Al2O3 interface, which has shown potential for normally-off metal oxide semiconductor field effect transistor with limited interface state density. The paper details the fabrication of OH-terminated (111) diamond/Al2O3 metal oxide semiconductor capacitors, describes an original method combining transfer length measurements with capacitance-voltage and frequency analysis, and discusses the extraction of interface trap density (Diit) and their energy distribution. The energy distribution of Diit was estimated using the conductance method, indicating that Diit was in the range of (0.7-0.9) x 1012 cm-2eV-1 within 0.34-0.49 eV from EV of diamond. Lastly the electron affinity was estimated to be e%(111)-OH = 0.36 eV, the first experimental value for the electron affinity of OH terminated (111) oriented diamond. The results are compared with existing literature to provide insights into the optimization of diamond-based metal oxide semiconductor devices.

Power electronics, a pivotal field orchestrating electrical energy flow in the modern world, deals with efficient conversion, control, and management of electrical power across diverse applications. While its scope encompasses circuits for energy conversion, its challenges include transporting electrical energy over extended distances. Focusing on electrical‐to‐electrical conversions, the goal is minimal loss for delivering maximum power. The article explores the intricacies of power electronics, presenting key equations, and concepts. The current global power electronics market witnesses growth, driven by demand for energy‐efficient technologies, renewables integration, and the rise of electric vehicles. Future trends indicate continued growth, driven by renewable energy systems, and electric vehicles. Wide bandgap semiconductors, play a crucial role, with ultra‐wide bandgap semiconductors like diamond emerging as potential disruptors. A comparative analysis of semiconductor properties reveals diamond's unique attributes. Despite its challenges, diamond shows promise for power electronic applications, with ongoing research on components like Schottky diodes. Thermal considerations, substrate limitations, and dislocation challenges are discussed, emphasizing the need for advancements to harness the full potential of diamond in power electronics. Finally, some inputs about the importance of overcoming these challenges for the successful integration of diamond in power electronic systems are given.

Due to its capacity to achieve nanometre-scale machining and lithography, a focused ion beam (FIB) is an extended tool for semiconductor device fabrication and development, in particular, for diamond-based devices. However, some technological steps are still not fully optimized for its use. Indeed, ion implantation seems to affect the crystalline structure and electrical properties of diamond. For this study, a boron-doped ([B] similar to 10(17) atomscm(-3)) diamond layer grown by chemical vapour deposition was irradiated using Ga+ by FIB, with 1 nA current and 5, 20, and 30 keV of acceleration voltage. The Ga+ implanted diamond layer has been analysed through cathodoluminescence (CL) and scanning transmission electron microscopy (STEM)-related techniques. The beam penetration depth has been simulated by Monte Carlo calculations of both Ga+ (FIB) and e(-) (CL) beams at different energies. The comparative CL analysis of the layer as-grown and after implantation revealed peaks related to defects, such as A band, H3 centre, and defects present in the green band region. The STEM studies for the 30 keV implanted sample showed that the diamond lattice is affected by the damage, evidencing amorphisation in the layer with a sp(2)/sp(3) ratio of 1.37, estimated by electron energy loss spectroscopy. Therefore, this study highlights the effects of the Ga+ implantation on the optical and structural characteristics of diamond, using different methods.

Diamond Schottky barrier diodes show promise for high voltage, power, and temperature applications due to the outstanding properties of diamond. However, there is still a lack of precise calculation for the Schottky barrier height requirements needed to display their ideal performances. In this work, we exploit semi-empirical models for resistivity and breakdown in p-type diamond, as well as numerical calculations for Schottky contact leakage currents, to outline the challenges and requirements of diamond Schottky diodes. We calculate the required barrier height and temperature stability for a Schottky contact to unleash the full potential of diamond and compare these requirements to the available experimental data. Additionally, we present the optimal performance of diamond Schottky barrier diodes and discuss their future prospects. Our results show that optimal performances of diamond Schottky barrier diodes are technologically accessible for the ultra-high voltage range (<5 kV) and moderately high temperature (550 K) and particularly efficient but more challenging at the high voltage range (1 kV). Lastly, we demonstrate that diamond Schottky barrier diodes are the most performing alternative at high temperature among wide band-gap semiconductors.

The emergence of wide band-gap (WBG) materials promises improved performance in semiconductor devices, but also presents significant technical challenges. Developing this immature technology and adapting marketready silicon-based technology to new materials requires a thorough understanding of the relationship between material properties and the final electrical performance of the component. In this work, we propose a model that relates generic material properties and device-specific parameters (such as doping level or thickness) to the final breakdown voltage and performance of unipolar vertical diodes. Our approach enables optimized device design and evaluation by connecting the electrical performance target with the optimal drift layer characteristics. This model can be applied universally to any material with known impact ionization coefficients, carrier mobility, and thermal activation energy. We focus on diamond as a paradigm for WBG materials, illustrating specific characteristics such as incomplete carrier ionization or elevated doping-dependent critical electric fields. Our model predicts that diamond-based vertical devices with 70 mu m layers and doping levels of 1.1015 cm-3 can sustain 20 kV.

In power electronics, the temperature of the device and its control are of major importance. Most of today's materials are particularly sensitive to this increase in temperature and performance is known to deteriorate. Moreover, if heat dissipation is poorly controlled, the component can enter into a self-heating regime which leads to its destruction. Diamond, however, has quite different performance levels because an increase to its tem-perature allows its resistivity to be reduced by the thermal activation of the carriers. It is therefore particularly important to control this temperature rise for an optimal use of diamond in a power device. The importance of self-heating in the use of these components will be shown through real-time coupled measurement of current, voltage, and temperature of a Schottky diode. An explanation of the characteristics will be given with a coupling of the thermal and electrical equations. Thus, although delicate to master, clever use of this electrothermal coupling makes it possible to envisage optimal or even original uses of these diamond devices.

Diamond lateral growth is a powerful technique for the design and fabrication of diamond-based power electronic devices. Growth orientation affects the diamond deposition in terms of growth rate, surface roughness, and impurity incorporation. It has been shown that the finally grown surface of a patterned substrate can be predesigned based on the growth conditions. Thus, simultaneous growth along different surface orientations yields regions with different properties. In line with this, the incorporation of boron in a microwave plasma enhanced chemical vapor deposition laterally deposited epilayer over a mesa patterned {100}-oriented diamond substrate was studied by cathodoluminescence. It was observed that laterally oriented facets were highly boron doped in contrast to the {100}-oriented surfaces, which did not show any bound exciton emission, related to the doping. This study shows that, by designing the initial pattern and tuning the conditions, it is possible to drive a selective incorporation of boron into the grown layer.

Schottky contacts have been used to fabricate normally- OFF lateral reverse-blocking MESFETs on p-type (boron-doped) O-terminated monocrystalline diamond. The devices utilized an ohmic source contact but both gate and drain contacts were Schottky in nature. Boron-doped p-channel diamond MESFETs reported to date display the less attractive normally- ON characteristics. Here, the normally- OFF transistor delivered a current level of ~1.5 $\mu $ Amm −1 at a negative ${V}_{\text {GS}}$ of 0.8 V and a transconductance ( ${g}_{m}$ ) of $16~\mu $ Smm −1 , measured at room temperature (RT); at a temperature of 425 K, these values rose to $\sim 70~\mu $ Amm −1 for ${I}_{\text {DS}}$ and a ${g}_{m}$ value of $260~\mu $ Smm −1 . In both cases, a negligible gate leakage current was measured with no breakdown apparent at the maximum field investigated here ( $3.7\times 10^{{5}}$ V/m −1 ). The Schottky gate demonstrates a well-behaved control of the channel even at higher temperatures. The high-temperature operation, normally- OFF behavior, and diamond’s inherent radiation hardness make this transistor promising for harsh environment applications.

gamma-Alumina is a promising candidate for fabricating the gate of the diamond metal oxide semiconductor field effect transistor based on oxygen termination due to its high bandgap of 6.7 eV and high static dielectric constant of 9. Besides these properties, having a sufficient barrier for holes is mandatory to avoid carriers leakage through the gate. However, the band offset of the diamond/alumina heterojunction can be affected by the alumina crystallinity and interface bonds, which depend on multiple factors such as deposition and annealing temperature or diamond surface treatment prior to deposition. In this work, the heterojunction of atomic layer deposited alumina and (1 0 0) p-diamond is studied using X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy studies reveal that the deposited alumina layer is 35 nm thick and present the gamma phase. The valence band offset between diamond and gamma-alumina is evaluated on a single sample with a new methodology based on an ion etching XPS depth profile. The obtained value for the valence band offset of diamond and gamma-alumina is 3.4 eV.

Concerning diamond-based electronic devices, the H-terminated diamond surface is one of the most used terminations as it can be obtained directly by using H2 plasma, which also is a key step for diamond growth by chemical vapour deposition (CVD). The resultant surfaces present a p-type surface conductive layer with interest in power electronic applications. However, the mechanism for this behavior is still under discussion. Upward band bending due to surface transfer doping is the most accepted model, but has not been experimentally probed as of yet. Recently, a downward band bending very near the surface due to shallow acceptors has been proposed to coexist with surface transfer doping, explaining most of the observed phenomena. In this work, a new approach to the measurement of band bending by angle-resolved X-ray photoelectron spectroscopy (ARXPS) is proposed. Based on this new interpretation, a downward band bending of 0.67 eV extended over 0.5 nm was evidenced on a (100) H-terminated diamond surface.

Advanced characterizations with combined analytical tools were carried out at the different stages of diamond heteroepitaxy on Ir/STO/Si (001) substrates. HRTEM and STEM-EELS revealed the presence of epitaxial nanometric diamond crystals after bias enhanced nucleation. UV Raman allowed estimating the diamond film quality and its strain at the early stages of heteroepitaxial growth. The crystalline structure and the strain within thick heteroepitaxial films were determined by XRD and CL investigations. A CL study of the cross-section provided the mapping of the dislocation network along the growth direction. Measurements performed on lateral Schottky diodes fabricated on a thick diamond film showed an excellent reproducibility on the substrate with a Schottky barrier height in good agreement with those obtained on homoepitaxial layers.

This paper proposes a system-level comparison between diamond and silicon carbide (SiC) power devices. It highlights the benefits of diamond semiconductors for power electronics applications. Actual diamond power devices were fabricated and characterised (DC, AC small-signal, large-signal power switching in a buck converter). Models of the diamond devices are discussed based on the experimental data, and the expected performances of the future diamond semiconductors in power converters are presented. These performances are compared to the commercialised SiC Schottky diodes for a given application. Our analysis shows that diamond devices can be used to increase the performance of power converters, especially at high temperatures. We demonstrate that for a junction temperature of 450 K, diamond semiconductors can divide the semiconductor losses and heatsink volume by three, in comparison with SiC devices. We also demonstrate that the switching frequency with diamond devices can be five times higher than with SiC devices, with lower total semiconductor losses and smaller heatsink in diamond-based power converters. This system-level analysis clearly shows the future improvements in the efficiency and power densities of power converters thanks to diamond power devices. The need for management of the specific junction temperature, which is required in order to exploit all of the properties of diamonds, is demonstrated and discussed.

Advanced characterizations with combined analytical tools were carried out at the different stages of diamond heteroepitaxy on Ir/STO/Si (001) substrates. HRTEM and STEM-EELS revealed the presence of epitaxial nanometric diamond crystals after bias enhanced nucleation. UV Raman allowed estimating the diamond film quality and its strain at the early stages of heteroepitaxial growth. The crystalline structure and the strain within thick heteroepitaxial films were determined by XRD and CL investigations. A CL study of the cross-section provided the mapping of the dislocation network along the growth direction. Measurements performed on lateral Schottky diodes fabricated on a thick diamond film showed an excellent reproducibility on the substrate with a Schottky barrier height in good agreement with those obtained on homoepitaxial layers.

A diamond MOSFET has been fabricated and characterized up to 250 degrees C. The fabrication process has been improved in order to significantly reduce the specific on resistance, down to 50 m Omega.cm(2), and the gate leakage current at high temperature. The maximum electrical field in diamond, at the breakdown value of 175V, is estimated to be higher than 5.4 MV/cm, with a boron doping of 2x10(17) cm(-3).

A diamond MOSFET has been fabricated and characterized up to 250°C. The fabrication process has been improved in order to significantly reduce the specific on resistance, down to 50 mΩ.cm 2 , and the gate leakage current at high temperature. The maximum electrical field in diamond, at the breakdown value of 175V, is estimated to be higher than 5.4 MV/cm, with a boron doping of 2×10 17 cm -3 .