Ion bombardment induced buried lateral growth: the key mechanism for the synthesis of single crystal diamond wafers

Formation of {111} oriented domains during the sputtering epitaxy growth of (001) oriented Iridium films

In the wafer-scale growth of Ir(001) on yttria-stabilized zirconia (YSZ) by magnetron sputtering epitaxy two kinds of {111} oriented domains are observed. One consists of sharp 'fjord'-shaped features in which four 90° alternated rotational variants of {111} are possible and the second one consists of islands with less defined shapes in which eight 45° alternated rotational variants can be found. Their formation occurs directly at the Ir/YSZ interface along incoherent grain boundaries, likely nucleating at local defects of the YSZ surface. In order to avoid these misoriented domains, process separation and proper etching pretreatment of the wafers both before and between the sputtering processes have been found to be the key strategy for achieving reproducibility and overall better material quality.

A Review of Diamond Materials and Applications in Power Semiconductor Devices

Diamond is known as the ultimate semiconductor material for electric devices with excellent properties such as an ultra-wide bandgap (5.47 eV), high carrier mobility (electron mobility 4000 cm2/V·s, hole mobility 3800 cm2/V·s), high critical breakdown electric field (20 MV/cm), and high thermal conductivity (22 W/cm·K), showing good prospects in high-power applications. The lack of n-type diamonds limits the development of bipolar devices; most of the research focuses on p-type Schottky barrier diodes (SBDs) and unipolar field-effect transistors (FETs) based on terminal technology. In recent years, breakthroughs have been made through the introduction of new structures, dielectric materials, heterogeneous epitaxy, etc. Currently, diamond devices have shown promising applications in high-power applications, with a BV of 10 kV, a BFOM of 874.6 MW/cm2, and a current density of 60 kA/cm2 already realized. This review summarizes the research progress of diamond materials, devices, and specific applications, with a particular focus on the development of SBDs and FETs and their use in high-power applications, aiming to provide researchers with the relevant intuitive parametric comparisons. Finally, the paper provides an outlook on the parameters and development directions of diamond power devices.

High-Temperature and High-Electron Mobility Metal-Oxide-Semiconductor Field-Effect Transistors Based on N-Type Diamond

Diamond holds the highest figure-of-merits among all the known semiconductors for next-generation electronic devices far beyond the performance of conventional semiconductor silicon. To realize diamond integrated circuits, both n- and p-channel conductivity are required for the development of diamond complementary metal-oxide-semiconductor (CMOS) devices, as those established for semiconductor silicon. However, diamond CMOS has never been achieved due to the challenge in n-type channel MOS field-effect transistors (MOSFETs). Here, electronic-grade phosphorus-doped n-type diamond epilayer with an atomically flat surface based on step-flow nucleation mode is fabricated. Consequently, n-channel diamond MOSFETs are demonstrated. The n-type diamond MOSFETs exhibit a high field-effect mobility around 150 cm2 V-1 s-1 at 573 K, which is the highest among all the n-channel MOSFETs based on wide-bandgap semiconductors. This work enables the development of energy-efficient and high-reliability CMOS integrated circuits for high-power electronics, integrated spintronics, and extreme sensors under harsh environments.

Diamond for High-Power, High-Frequency, and Terahertz Plasma Wave Electronics

High thermal conductivity and a high breakdown field make diamond a promising candidate for high-power and high-temperature semiconductor devices. Diamond also has a higher radiation hardness than silicon. Recent studies show that diamond has exceptionally large electron and hole momentum relaxation times, facilitating compact THz and sub-THz plasmonic sources and detectors working at room temperature and elevated temperatures. The plasmonic resonance quality factor in diamond TeraFETs could be larger than unity for the 240-600 GHz atmospheric window, which could make them viable for 6G communications applications. This paper reviews the potential and challenges of diamond technology, showing that diamond might augment silicon for high-power and high-frequency compact devices with special advantages for extreme environments and high-frequency applications.

Overcoming Copper Substrate Thermodynamic Limitations in Anode-Free Lithium Pouch Cells via In Situ Seed Implantation

Anode-free lithium metal batteries (AFLMBs) exhibit enhanced energy density and cost-effective manufacturing, albeit constrained by short lifespans due to inhomogeneous lithium nucleation and growth on the inherently lithiophobic Cu current collector. Although numerous attempts at Cu surface modifications aim to mitigate this thermodynamic limitation, they often result in substantial irreversible capacity loss and/or lack the stability required for practical applications. Here, we present an in situ seed implantation (ISI) strategy to address the aforementioned challenge. A 36 s ISI treatment created an ultrathin lithium metal layer, composed of uniform lithium nuclei with ∼100 nm in diameter, equating to 0.05 mAh cm-2, on the Cu substrate. This approach facilitates dense lithium deposition during cycles, effectively doubling the lifespan of an Ah-level 437 Wh kg-1 AFLMB. Our ISI strategy offers a straightforward and efficient solution that maintains battery energy density and manufacturing cost effectiveness, and its application extends beyond lithium metal.

A Study of the Radiation Tolerance and Timing Properties of 3D Diamond Detectors

We present a study on the radiation tolerance and timing properties of 3D diamond detectors fabricated by laser engineering on synthetic Chemical Vapor Deposited (CVD) plates. We evaluated the radiation hardness of the sensors using Charge Collection Efficiency (CCE) measurements after neutron fluences up to 1016 n/cm2 (1 MeV equivalent.) The radiation tolerance is significantly higher when moving from standard planar architecture to 3D architecture and increases with the increasing density of the columnar electrodes. Also, the maximum applicable bias voltage before electric breakdown increases significantly after high fluence irradiation, possibly due to the passivation of defects. The experimental analysis allowed us to predict the performance of the devices at higher fluence levels, well in the range of 1016 n/cm2. We summarize the recent results on the time resolution measurements of our test sensors after optimization of the laser fabrication process and outline future activity in developing pixel tracking systems for high luminosity particle physics experiments.

Electrical Characteristics of Diamond MOSFET with 2DHG on a Heteroepitaxial Diamond Substrate

In this work, hydrogen-terminated diamond (H-diamond) metal-oxide-semiconductor field-effect-transistors (MOSFETs) on a heteroepitaxial diamond substrate with an Al₂O₃ dielectric and a passivation layer were characterized. The full-width at half maximum value of the diamond (004) X-ray rocking curve was 205.9 arcsec. The maximum output current density and transconductance of the MOSFET were 172 mA/mm and 10.4 mS/mm, respectively. The effect of a low-temperature annealing process on electrical properties was also investigated. After the annealing process in N₂ atmosphere, the threshold voltage (V_th) and flat-band voltage (V_FB) shifts to negative direction due to loss of negative charges. After annealing at 423 K for 3 min, the maximum value of hole field effective mobility (μ_eff) increases by 27% at V_th − V_GS = 2 V. The results, which are not inferior to those based on homoepitaxial diamond, promote the application of heteroepitaxial diamond in the field of electronic devices.

Thickness Impact on the Morphology, Strain Relaxation and Defects of Diamond Heteroepitaxially Grown on Ir/Al2O3 Substrates

This paper investigates the formation and propagation of defects in the heteroepitaxial growth of single-crystal diamond with a thick film achieving 500 µm on Ir (001)/Al₂O₃ substrate. The growth of diamond follows the Volmer-Weber mode, i.e., initially shows the islands and subsequently coalesces to closed films. The films' strain imposed by the substrate gradually relaxed as the film thickness increased. It was found that defects are mainly located at the diamond/Ir interface and are then mainly propagated along the [001] direction from the nucleation region. Etching pits along the [001] direction formed by H₂/O₂ plasma treatment were used to show defect distribution at the diamond/Ir/Al₂O₃ interface and in the diamond bulk, which revealed the reduction of etching pit density in diamond thick-film surface. These results show the evident impact of the thickness on the heteroepitaxially grown diamond films, which is of importance for various device applications.

Tunable and Transferable Diamond Membranes for Integrated Quantum Technologies

Color centers in diamond are widely explored as qubits in quantum technologies. However, challenges remain in the effective and efficient integration of these diamond-hosted qubits in device heterostructures. Here, nanoscale-thick uniform diamond membranes are synthesized via "smart-cut" and isotopically (¹²C) purified overgrowth. These membranes have tunable thicknesses (demonstrated 50 to 250 nm), are deterministically transferable, have bilaterally atomically flat surfaces (R_q ≤ 0.3 nm), and bulk-diamond-like crystallinity. Color centers are synthesized via both implantation and in situ overgrowth incorporation. Within 110-nm-thick membranes, individual germanium-vacancy (GeV^-) centers exhibit stable photoluminescence at 5.4 K and average optical transition line widths as low as 125 MHz. The room temperature spin coherence of individual nitrogen-vacancy (NV^-) centers shows Ramsey spin dephasing times (T₂^*) and Hahn echo times (T₂) as long as 150 and 400 μs, respectively. This platform enables the straightforward integration of diamond membranes that host coherent color centers into quantum technologies.

Diamond for Electronics: Materials, Processing and Devices

Progress in power electronic devices is currently accepted through the use of wide bandgap materials (WBG). Among them, diamond is the material with the most promising characteristics in terms of breakdown voltage, on-resistance, thermal conductance, or carrier mobility. However, it is also the one with the greatest difficulties in carrying out the device technology as a result of its very high mechanical hardness and smaller size of substrates. As a result, diamond is still not considered a reference material for power electronic devices despite its superior Baliga’s figure of merit with respect to other WBG materials. This review paper will give a brief overview of some scientific and technological aspects related to the current state of the main diamond technology aspects. It will report the recent key issues related to crystal growth, characterization techniques, and, in particular, the importance of surface states aspects, fabrication processes, and device fabrication. Finally, the advantages and disadvantages of diamond devices with respect to other WBG materials are also discussed.

Surface Morphology and Microstructure Evolution of Single Crystal Diamond during Different Homoepitaxial Growth Stages

Homoepitaxial growth of step-flow single crystal diamond was performed by microwave plasma chemical vapor deposition system on high-pressure high-temperature diamond substrate. A coarse surface morphology with isolated particles was firstly deposited on diamond substrate as an interlayer under hillock growth model. Then, the growth model was changed to step-flow growth model for growing step-flow single crystal diamond layer on this hillock interlayer. Furthermore, the surface morphology evolution, cross-section and surface microstructure, and crystal quality of grown diamond were evaluated by scanning electron microscopy, high-resolution transmission electron microcopy, and Raman and photoluminescence spectroscopy. It was found that the surface morphology varied with deposition time under step-flow growth parameters. The cross-section topography exhibited obvious inhomogeneity in crystal structure. Additionally, the diamond growth mechanism from the microscopic point of view was revealed to illustrate the morphological and structural evolution.

Low-pressure diamond: from the unbelievable to technical products

The idea to grow diamond from the gas phase was born in the 1950s but it took about 30 years until first diamond layers directly grown from the gas phase on substrates were shown in Japan by Matsumoto and co-workers. During the first years of research the function of atomic hydrogen, various growth methods and process parameters were investigated. Research was primarily focused on applications for wear-resistant tools. For this topic the interactions of substrates like hardmetals and ceramics, with diamond deposition gas atmosphere, were investigated. Beside its superior hardness, diamond exhibits the highest heat conductivity, high transparency, high chemical inertness and suitable semiconducting properties. The various requirements for the areas of application of diamond required a division of diamond research into corresponding sub-areas. The hot-filament method is used mainly for wear applications, because it is highly suited to coat complex geometries, but the diamond contains some impurities. Another method is the microwave plasma system which allows the growth of pure diamond used for optical windows and applications requiring high thermal conductivity. Other research areas investigated include doped diamond for microelectronic or electrochemical applications (e.g. waste water treatment); ballas (polycrystalline, spherical diamond), NCD (nanocrystalline diamond) and UNCD (ultra-nanocrystalline diamond) for wear applications.

It should be noted that CVD (chemical vapour deposition) diamond synthesis has reached the stage of industrial production and several companies are selling different diamond products. This work is intended to convey to the reader that CVD diamond is an industrially manufactured product that can be used in many ways. With correspondingly low costs for this diamond, new innovative applications appear possible.

Nucleation of diamond films on heterogeneous substrates: a review

Diamond thin films are known to have properties similar to bulk diamond and have applications in both industry and fundamental studies in academia. The high surface energy of diamond makes it extremely difficult to grow diamond films on foreign substrates. Hence, to grow diamond films on non-diamond substrates, a nucleation step is needed. In this review various techniques used for diamond nucleation/seeding will be discussed. At present electrostatic seeding by diamond nanoparticles is the most commonly used seeding technique for nanocrystalline growth. In this technique the substrate is dipped in a nanodiamond solution to form a mono layer of diamond seeds. These seeds when exposed to appropriate conditions grow to form diamond layers. This technique is suitable for most substrates. For heteroepitaxial growth, bias enhanced nucleation is the primary technique. In this technique the substrate is biased to form diamond nuclei in the initial stages of growth. This technique can be used for any conducting flat surface. For growth on ceramics, polishing by diamond grit or electrostatic seeding can be used. Polishing the ceramics with diamond powder leaves small diamond particles embedded in the substrate. These small particles then act as seeds for subsequent diamond growth. Apart from these techniques, chemical nucleation, interlayer driven nucleation and mixed techniques have been discussed. The advantages and disadvantages of individual techniques have also been discussed.

Growth of diamond film on heterogeneous substrates assisted by nucleation/seeding.

Competition between diamond nucleation and growth under bias voltage by microwave plasma chemical vapor deposition

A competition between diamond nucleation and growth is proposed in which the surface and bulk nucleation coexist and compete.

Recent Advances in Single Crystal Diamond Device Fabrication for Photonics, Sensing and Nanomechanics

In the last two decades, the use of diamond as a material for applications in nanophotonics, optomechanics, quantum information, and sensors tremendously increased due to its outstanding mechanical properties, wide optical transparency, and biocompatibility. This has been possible owing to advances in methods for growth of high-quality single crystal diamond (SCD), nanofabrication methods and controlled incorporation of optically active point defects (e.g., nitrogen vacancy centers) in SCD. This paper reviews the recent advances in SCD nano-structuring methods for realization of micro- and nano-structures. Novel fabrication methods are discussed and the different nano-structures realized for a wide range of applications are summarized. Moreover, the methods for color center incorporation in SCD and surface treatment methods to enhance their properties are described. Challenges in the upscaling of SCD nano-structure fabrication, their commercial applications and future prospects are discussed.

Effect of Substrate Holder Design on Stress and Uniformity of Large-Area Polycrystalline Diamond Films Grown by Microwave Plasma-Assisted CVD

In this work, the substrate holders of three principal geometries (flat, pocket, and pedestal) were designed based on E-field simulations. They were fabricated and then tested in microwave plasma-assisted chemical vapor deposition process with the purpose of the homogeneous growth of 100-μm-thick, low-stress polycrystalline diamond film over 2-inch Si substrates with a thickness of 0.35 mm. The effectiveness of each holder design was estimated by the criteria of the PCD film quality, its homogeneity, stress, and the curvature of the resulting “diamond-on-Si” plates. The structure and phase composition of the synthesized samples were studied with scanning electron microscopy and Raman spectroscopy, the curvature was measured using white light interferometry, and the thermal conductivity was measured using the laser flash technique. The proposed pedestal design of the substrate holder could reduce the stress of the thick PCD film down to 1.1–1.4 GPa, which resulted in an extremely low value of displacement for the resulting “diamond-on-Si” plate of Δh = 50 μm. The obtained results may be used for the improvement of already existing, and the design of the novel-type, MPCVD reactors aimed at the growth of large-area thick homogeneous PCD layers and plates for electronic applications.

Thick, Adherent Diamond Films on AlN with Low Thermal Barrier Resistance

The growth of >100-μm-thick diamond layers adherent on aluminum nitride with low thermal boundary resistance between diamond and AlN is presented in this work. The thermal barrier resistance was found to be in the range of 16 m²·K/GW, which is a large improvement on the current state-of-the-art. While thick films failed to adhere on untreated AlN films, AlN films treated with hydrogen/nitrogen plasma retained the thick diamond layers. Clear differences in ζ-potential measurement confirm surface modification due to hydrogen/nitrogen plasma treatment. An increase in non-diamond carbon in the initial layers of diamond grown on pretreated AlN is seen by Raman spectroscopy. The presence of non-diamond carbon has minimal effect on the thermal barrier resistance. The surfaces studied with X-ray photoelectron spectroscopy revealed a clear distinction between pretreated and untreated samples. The surface aluminum goes from a nitrogen-rich environment to an oxygen-rich environment after pretreatment. A clean interface between diamond and AlN is seen by cross-sectional transmission electron microscopy.

Asymmetric Phosphorus Incorporation in Homoepitaxial P-Doped (111) Diamond Revealed by Photoelectron Holography

Diamond has two crystallographically inequivalent sites in the unit cell. In doped diamond, dopant occupation in the two sites is expected to be equal. Nevertheless, preferential dopant occupation during growth under nonequilibrium conditions is of fundamental importance, for example, to enhance the properties of nitrogen-vacancy (N-V) centers; therefore, this is a promising candidate for a qubit. However, the lack of suitable experimental techniques has made it difficult to study the crystal- and chemical-site-resolved local structures of dopants. Here, we confirm the identity of two chemical sites with asymmetric dopant incorporation in the diamond structure, via the photoelectron holography (PEH) of heavily phosphorus (P)-doped diamond prepared by chemical vapor deposition. One is substitutionally incorporated P with preferential site occupations and the other can be attributed to a PV split vacancy complex with preferential orientation. The present study shows that PEH is a valuable technique to study the local structures around dopants with a resolution of crystallographically inequivalent but energetically equivalent sites/orientations. Such information provides strategies to improve the properties of dopant related-complexes in which alignment is crucial for sensing of magnetic field or quantum spin register using N-V centers in diamond.

Fabrication of capacitive pressure sensor using single crystal diamond cantilever beam

Fabrication of single crystal diamond capacitive pressure sensor is presented. Firstly, the single crystal diamond cantilever beam was formed on HPHT diamond substrate by using selective high-energy ion implantation, metal patterning, ICP etching and electrochemical etching techniques. Secondly, on this diamond cantilever beam, the desired electrode patterns were processed with photolithography and metal evaporation methods. Furthermore, the displacements of cantilever beam under different pressure conditions were investigated by atomic force microscopy. The capacitance-voltage curves of single crystal diamond cantilever beam and substrate under different force loading conditions were measured by using Agilent B1505A parameter analyzer. The results show that sensitivity increases with the enlargement of electrode area of cantilever beam, and decreases with the rise of measurement frequency.

Polycrystalline Diamond Thin-Film Waveguides for Mid-Infrared Evanescent Field Sensors

Photonic design and optimization of thin-film polycrystalline diamond waveguides are shown, serving as advanced evanescent field transducers in the mid-infrared fingerprint regime (2000-909 cm^-1; 5-11 μm). Design constraints inherent to optical/system considerations and the material were implemented in a finite element method (FEM)-based simulation method that allowed three-dimensional modeling of the overall structure. Thus, lateral mode confinement, attenuation in the direction of radiation propagation, and physical resilience were evaluated. In a final step, the designed structures were fabricated, and their utility in combination with a broadly tunable external cavity quantum cascade laser for chemical sensing of a liquid phase analyte was demonstrated.