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DOE OSTI2015

Fabrication of diamond based sensors for use in extreme environments

Electrical and magnetic sensors can be lithographically fabricated on top of diamond substrates and encapsulated in a protective layer of chemical vapor deposited single crystalline diamond. This process when carried out on single crystal diamond anvils employed in high pressure research is termed as designer diamond anvil fabrication. These designer diamond anvils allow researchers to study electrical and magnetic properties of materials under extreme conditions without any possibility of damaging the sensing elements. We describe a novel method for the fabrication of designer diamond anvils with the use of maskless lithography and chemical vapor deposition in this paper. This method can be utilized to produce diamond based sensors which can function in extreme environments of high pressures, high and low temperatures, corrosive and high radiation conditions. Here, we demonstrate applicability of these diamonds under extreme environments by performing electrical resistance measurements during superconducting transition in rare earth doped iron-based compounds under high pressures to 12 GPa and low temperatures to 10 K.

36 MATERIALS SCIENCE↗

DOE OSTI2020

A Study of the Radiation Tolerance of CVD Diamond to 70 MeV Protons, Fast Neutrons and 200 MeV Pions

We measured the radiation tolerance of commercially available diamonds grown by the Chemical Vapor Deposition process by measuring the charge created by a 120 GeV hadron beam in a 50 μm pitch strip detector fabricated on each diamond sample before and after irradiation. We irradiated one group of samples with 70 MeV protons, a second group of samples with fast reactor neutrons (defined as energy greater than 0.1 MeV), and a third group of samples with 200 MeV pions, in steps, to (8.8±0.9) × 1015 protons/cm2, (1.43±0.14) × 1016 neutrons/cm2, and (6.5±1.4) × 1014 pions/cm2, respectively. By observing the charge induced due to the separation of electron–hole pairs created by the passage of the hadron beam through each sample, on an event-by-event basis, as a function of irradiation fluence, we conclude all datasets can be described by a first-order damage equation and independently calculate the damage constant for 70 MeV protons, fast reactor neutrons, and 200 MeV pions. We find the damage constant for diamond irradiated with 70 MeV protons to be 1.62±0.07(stat)±0.16(syst)× 10−18 cm2/(p μm), the damage constant for diamond irradiated with fast reactor neutrons to be 2.65±0.13(stat)±0.18(syst)× 10−18 cm2/(n μm), and the damage constant for diamond irradiated with 200 MeV pions to be 2.0±0.2(stat)±0.5(syst)× 10−18 cm2/(π μm). The damage constants from this measurement were analyzed together with our previously published 24 GeV proton irradiation and 800 MeV proton irradiation damage constant data to derive the first comprehensive set of relative damage constants for Chemical Vapor Deposition diamond. We find 70 MeV protons are 2.60 ± 0.29 times more damaging than 24 GeV protons, fast reactor neutrons are 4.3 ± 0.4 times more damaging than 24 GeV protons, and 200 MeV pions are 3.2 ± 0.8 more damaging than 24 GeV protons. We also observe the measured data can be described by a universal damage curve for all proton, neutron, and pion irradiations we performed of Chemical Vapor Deposition diamond. Finally, we confirm the spatial uniformity of the collected charge increases with fluence for polycrystalline Chemical Vapor Deposition diamond, and this effect can also be described by a universal curve.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Boron isotopes in blue diamond record seawater-derived fluids in the lower mantle

Boron is a quintessential crustal element but its conspicuous presence in diamond – a mantle mineral – raises questions about potential subduction pathways for boron and other volatiles. It has been a long-standing goal to characterize the isotopic composition of boron in blue, boron-bearing (Type IIb) diamonds to reveal its origin. Mineral inclusions indicate that Type IIb diamonds crystallize at transition zone to lower mantle depths, meaning that if the boron is subducted it would trace a pathway of volatile elements into the deep mantle. Here, using off-line laser ablation sampling, we present the first boron isotope compositions, along with trace element contents and carbon isotope compositions, of a suite of blue diamonds mainly sourced from the Cullinan diamond mine in South Africa. The ten analyzed blue diamonds have a wide range in δ 11 B, between -9.2 ± 2‰ and -0.5 ± 2‰, compared to the more restricted range for mid-ocean ridge basalts (-7.1 ± 0.9‰). Carbon isotope values for the blue diamonds range between -20.6 and -1.8‰, with a mode at -17‰, significantly more negative than the main mantle mode at -5‰. Combined, the boron and carbon isotope compositions require fluid input from subducted oceanic lithosphere down into deep mantle source regions of blue diamonds. This finding highlights a deep subduction pathway for volatiles to stoke the source regions of deeply-derived magmas.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Direct-bonded diamond membranes for heterogeneous quantum and electronic technologies

Diamond has superlative material properties for a broad range of quantum and electronic technologies. However, heteroepitaxial growth of single crystal diamond remains limited, impeding integration and evolution of diamond-based technologies. Here, we directly bond single-crystal diamond membranes to a wide variety of materials including silicon, fused silica, sapphire, thermal oxide, and lithium niobate. Our bonding process combines customized membrane synthesis, transfer, and dry surface functionalization, allowing for minimal contamination while providing pathways for near unity yield and scalability. We generate bonded crystalline membranes with thickness as low as 10 nm, sub-nm interfacial regions, and nanometer-scale thickness variability over 200 by 200 μm 2 areas. We measure spin coherence times T 2 for nitrogen vacancy centers in 150 nm-thick bonded membranes of up to 623 ± 21 μs, suitable for advanced quantum applications. We demonstrate multiple methods for integrating high quality factor nanophotonic cavities with the diamond heterostructures, highlighting the platform versatility in quantum photonic applications. Furthermore, we show that our ultra-thin diamond membranes are compatible with total internal reflection fluorescence (TIRF) microscopy, which enables interfacing coherent diamond quantum sensors with living cells while rejecting unwanted background luminescence. The processes demonstrated herein provide a full toolkit to synthesize heterogeneous diamond-based hybrid systems for quantum and electronic technologies.

color center↗

DOE OSTI2014

Focused-ion-beam overlay-patterning of three-dimensional diamond structures for advanced single-photon properties

Sources of single photons are of fundamental importance in many applications as to provide quantum states for quantum communication and quantum information processing. Color centers in diamond are prominent candidates to generate and manipulate quantum states of light, even at room temperature. However, the efficiency of photon collection of the color centers in bulk diamond is greatly reduced by refraction at the diamond/air interface. To address this issue, diamond structuring has been investigated by various methods. Among them, focused-ion-beam (FIB) direct patterning has been recognized as the most favorable technique. But it has been noted that diamond tends to present significant challenges in FIB milling, e.g., the susceptibility of forming charging related artifacts and topographical features. In this work, periodically-positioned-rings and overlay patterning with stagger-superimposed-rings were proposed to alleviate some problems encountered in FIB milling of diamond, for improved surface morphology and shape control. Cross-scale network and uniform nanostructure arrays have been achieved in single crystalline diamond substrates. High quality diamond solid immersion lens and nanopillars were sculptured with a nitrogen-vacancy center buried at the desired position. Compared with the film counterpart, an enhancement of about ten folds in single photon collection efficiency was achieved with greatly improved signal to noise ratio. All these results indicate that FIB milling through over-lay patterning could be an effective approach to fabricate diamond structures, potentially for quantum information studies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Thermal conductivity changes upon neutron transmutation of {sup 10}B doped diamond

{sup 10}B doped p-type diamond samples were subjected to neutron transmutation reaction using thermal neutron flux of 0.9 × 10{sup 13} cm{sup −2} s{sup −1} and fast neutron flux of 0.09 × 10{sup 13} cm{sup −2} s{sup −1}. Another sample of epilayer grown on type IIa (110) single crystal diamond substrate was subjected to equal thermal and fast neutron flux of 10{sup 14} cm{sup −2} s{sup −1}. The defects in the diamond samples were previously characterized by different methods. In the present work, thermal conductivity of these diamond samples was determined at room temperature by transient thermoreflectance method. The thermal conductivity change in the samples as a function of neutron fluence is explained by the phonon scattering from the point defects and disordered regions. The thermal conductivity of the diamond samples decreased more rapidly initially and less rapidly for larger neutron fluence. In addition, the thermal conductivity in type IIb diamond decreased less rapidly with thermal neutron fluence compared to the decrease in type IIa diamond subjected to fast neutron fluence. It is concluded that the rate of production of defects during transmutation reaction is slower when thermal neutrons are used. The thermal conductivity of epilayer of diamond subjected to high thermal and fast neutron fluence is associated with the covalent carbon network in the composite structure consisting of disordered carbon and sp{sup 2} bonded nanocrystalline regions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Novel phase of carbon, ferromagnetism, and conversion into diamond

We report the discovery of a new phase of carbon (referred to as Q-carbon) and address fundamental issues related to direct conversion of carbon into diamond at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon is formed as result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs. T) of carbon and show that by rapid quenching kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled carbon at atmospheric pressure in air. It is shown that nanosecond laser heating of diamond-like amorphous carbon on sapphire, glass, and polymer substrates can be confined to melt carbon in a super undercooled state. By quenching the carbon from the super undercooled state, we have created a new state of carbon (Q-carbon) from which nanodiamond, microdiamond, microneedles, and single-crystal thin films are formed depending upon the nucleation and growth times allowed for diamond formation. The Q-carbon quenched from liquid is a new state of solid carbon with a higher mass density than amorphous carbon and a mixture of mostly fourfold sp{sup 3} (75%–85%) with the rest being threefold sp{sup 2} bonded carbon (with distinct entropy). It is expected to have new and improved mechanical hardness, electrical conductivity, chemical, and physical properties, including room-temperature ferromagnetism (RTFM) and enhanced field emission. Here we present interesting results on RTFM, enhanced electrical conductivity and surface potential of Q-carbon to emphasize its unique properties. The Q-carbon exhibits robust bulk ferromagnetism with estimated Curie temperature of about 500 K and saturation magnetization value of 20 emu g{sup −1}. From the Q-carbon, diamond phase is nucleated and a variety of micro- and nanostructures and large-area single-crystal diamond sheets are grown by allowing growth times as needed. Subsequent laser pulses can be used to grow nanodiamond into microdiamond and nucleate other nanostructures of diamond on the top of existing microdiamond and create novel nanostructured materials. The microstructural details provide insights into the mechanism of formation of nanodiamond, microdiamond, nanoneedles, microneedles, and single-crystal thin films. This process allows carbon-to-diamond conversion and formation of useful nanostructures and microstructures at ambient temperatures in air at atmospheric pressure on practical and heat-sensitive substrates in a controlled way without need for any catalysts and hydrogen to stabilize sp{sup 3} bonding for diamond formation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Photoconductive Switch with High Sub-Bandgap Responsivity in Nitrogen-Doped Diamond

To evaluate nitrogen-doped diamond as a candidate for Photoconductive Semiconductor Switches (PCSS) triggered in the sub-bandgap visible range, we have fabricated and tested diamond PCSS from a set of diamond grades of varying nitrogen concentration. The nitrogen-doped diamond PCSS have higher responsivity than other diamond optoelectronic devices in the visible range. We present a novel demonstration of sub-bandgap triggered diamond PCSS, which when scaled to higher voltage, can compete with and even surpass performance of existing ultraviolet-triggered diamond PCSS. This work suggests that nitrogen-doped diamond is a promising candidate for high-power, fast optoelectronic devices.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Low-temperature synthesis of diamond films by photoemission-assisted plasma-enhanced chemical vapor deposition

Photoemission-assisted plasma-enhanced chemical vapor deposition (PA-PECVD), a process in which photoelectrons emitted from a substrate irradiated with ultraviolet light are utilized as a trigger for DC discharge, was investigated in this study; specifically, the DC discharge characteristics of PA-PECVD were examined for an Si substrate deposited in advance through hot-filament chemical vapor deposition with a nitrogen-doped diamond layer of thickness ∼1 μm. Using a commercially available Xe excimer lamp (hν = 7.2 eV) to illuminate the diamond surface with and without hydrogen termination, the photocurrents were found to be 3.17 × 10{sup 12} and 2.11 × 10{sup 11} electrons/cm{sup 2}/s, respectively. The 15-fold increase in photocurrent was ascribed to negative electron affinity (NEA) caused by hydrogen termination on the diamond surfaces. The DC discharge characteristics revealed that a transition bias voltage from a Townsend-to-glow discharge was considerably decreased because of NEA (from 490 to 373 V for H{sub 2} gas and from 330 to 200 V for Ar gas), enabling a reduction in electric power consumption needed to synthesize diamond films through PA-PECVD. In fact, the authors have succeeded in growing high-quality diamond films of area 2.0 cm{sup 2} at 540 °C with a discharge power of only 1.8 W, plasma voltage of 156.4 V, and discharge current of 11.7 mA under the glow discharge of CH{sub 4}/H{sub 2}/Ar mixed gases. In addition to having only negligible amounts of graphite and amorphous carbon, the diamond films exhibit a relatively high diamond growth rate of 0.5 μm/h at temperatures as low as 540 °C, which is attributed to Ar{sup +} ions impinging on the diamond surface, and causing the removal of hydrogen atoms from the surface through sputtering. This process leads to enhanced CH{sub x} radical adsorption, because the sample was applied with a negative potential to accelerate photoelectrons in PA-PECVD.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Structure Formation of Hexagonal Diamond: Ab Initio Calculations

The formation of structure of hexagonal diamond from graphite and cubic diamond is simulated with the density functional theory. Orthorhombic AB graphite transforms into hexagonal diamond under uniaxial compression at pressures above 61 GPa. The pressure should be higher than 57 GPa to form hexagonal diamond from AA graphite. Another possible way to obtain hexagonal diamond is uniaxial compression of cubic diamond under pressures from 300 to 380 GPa. The theoretical calculations were used to interpret the diffraction data obtained after X-ray diffraction and electron microscopic analysis of natural and synthetic diamond-like materials. We found that there are no crystals with ideal cubic and hexagonal structures in diamond-like carbon materials, and their structure is characterized by random packing of molecular layers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Superior wear resistance of diamond and DLC coatings

As the hardest known material, diamond and its coatings continue to generate significant attention for stringent applications involving extreme tribological conditions. Likewise, diamond-like carbon (DLC, especially the tetragonal amorphous carbon, ta-C) coatings have also maintained a high level interest for numerous industrial applications where efficiency, performance, and reliability are of great importance. Additionally, the strong covalent bonding or sp 3 -hybridizaiton in diamond and ta-C coatings assures high mechanical hardness, stiffness, chemical and thermal stability that make them well-suited for harsh tribological conditions involving high-speeds, loads, and temperatures. In particular, unique chemical and mechanical nature of diamond and ta-C surfaces plays an important role in their unusual friction and wear behaviors. As with all other tribomaterials, both diamond and ta-C coatings strongly interact with the chemical species in their surroundings during sliding and hence produce a chemically passive top surface layer which ultimately determines the extent of friction and wear. Thick micro-crystalline diamond films are most preferred for tooling applications, while thinner nano/ultranano-crysalline diamond films are well-suited for mechanical devices ranging from nano- (such as NEMS) to micro- (MEMS and AFM tips) as well as macro-scale devices including mechanical pump seals. The ta-C coatings have lately become indispensable for a variety of automotive applications and are used in very large volumes in tappets, piston pins, rings, and a variety of gears and bearings, especially in the Asian market. This paper is intended to provide a comprehensive overview of the recent developments in tribology of super-hard diamond and DLC (ta-C) films with a special emphasis on their friction and wear mechanisms that are key to their extraordinary tribological performance under harsh tribological conditions. Finally, based on the results of recent studies, the paper will also attempt to highlight what lies ahead for these films in tribology and other demanding industrial applications.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Strength and deformation of shocked diamond single crystals: Orientation dependence

Understanding and quantifying the strength or elastic limit of diamond single crystals is of considerable scientific and technological importance, and has been a subject of long standing theoretical and experimental interest. To examine the effect of crystalline anisotropy on strength and deformation of shocked diamond single crystals, plate impact experiments were conducted to measure wave profiles at various elastic impact stresses up to ~120 GPa along [110] and [111] crystal orientations. Using laser interferometry, particle velocity histories and shock velocities in the diamond samples were measured and were compared with similar measurements published previously for shock compression along the [100] direction. Wave profiles for all three orientations showed large elastic wave amplitudes followed by time-dependent inelastic deformation. From the measured wave profiles, the elastic limits were determined under well characterized uniaxial strain loading conditions. The measured elastic wave amplitudes for the [110] and [111] orientations were lower for higher elastic impact stress (stress attained for an elastic diamond response), consistent with the result reported previously for [100] diamond. The maximum resolved shear stress (MRSS) on the {111}<110> slip systems was determined for each orientation, revealing significant orientation dependence. The MRSS values for the [100] and [110] orientations (~33 GPa) are 25-30% of theoretical estimates; the MRSS value for the [111] orientation is significantly lower (~23 GPa). Our results demonstrate that the MRSS depends strongly on the stress component normal to the {111} planes or the resolved normal stress (RNS), suggesting that the RNS plays a key role in inhibiting the onset of inelastic deformation. Lower elastic wave amplitudes at higher peak stress and the effect of the RNS are inconsistent with typical dislocation slip mechanisms of inelastic deformation, suggesting instead an inelastic response characteristic of shocked brittle solids. The present results show that the elastic limit (or material strength) of diamond single crystals cannot be described using traditional isotropic approaches, and typical plasticity models cannot be used to describe the inelastic deformation of diamond. Analysis of the measured wave profiles beyond the elastic limit, including characterization of the peak state, requires numerical simulations that incorporate a time-dependent, anisotropic, inelastic deformation response. Development of such a material description for diamond is an important need.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Shock compression of diamond single crystals to 120 GPa: Refractive index and nonlinear photoelasticity

The optical response of transparent solids at extreme conditions is important for both fundamental science and many applications. Strong transparent solids are of particular interest for use as optical windows in dynamic compression experiments. Due to diamond’s exceptional strength and optical properties, laser-driven shock experiments and plate impact experiments were carried out to examine the diamond optical response for shock wave compression along two different crystal orientations. Using laser interferometry at 532 nm and 1550 nm wavelengths, optical transparency was observed and refractive indices were determined for [100] diamond at stresses up to 119 GPa and for [111] diamond at stresses up to 87 GPa. From these results, the nonlinear photoelastic response for [100] and [111] diamond was determined, revealing significant dependence on both crystal orientation and laser wavelength. To enable [100] diamond as an interferometry window in dynamic compression experiments, the requisite window corrections were determined for 532 nm and 1550 nm wavelengths. Because of diamond’s excellent x-ray transparency, the present findings will be particularly useful for incorporating [100] diamonds as windows in dynamic compression experiments involving x-ray diffraction or other x-ray diagnostics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1995

Diamond thin film temperature and heat-flux sensors

Diamond film temperature and heat-flux sensors are developed using a technology compatible with silicon integrated circuit processing. The technology involves diamond nucleation, patterning, doping, and metallization. Multi-sensor test chips were designed and fabricated to study the thermistor behavior. The minimum feature size (device width) for 1st and 2nd generation chips are 160 and 5 micron, respectively. The p-type diamond thermistors on the 1st generation test chip show temperature and response time ranges of 80-1270 K and 0.29-25 microseconds, respectively. An array of diamond thermistors, acting as heat flux sensors, was successfully fabricated on an oxidized Si rod with a diameter of 1 cm. Some problems were encountered in the patterning of the Pt/Ti ohmic contacts on the rod, due mainly to the surface roughness of the diamond film. The use of thermistors with a minimum width of 5 micron (to improve the spatial resolution of measurement) resulted in lithographic problems related to surface roughness of diamond films. We improved the mean surface roughness from 124 nm to 30 nm by using an ultra high nucleation density of 10(exp 11)/sq cm. To deposit thermistors with such small dimensions on a curved surface, a new 3-D diamond patterning technique is currently under development. This involves writing a diamond seed pattern directly on the curved surface by a computer-controlled nozzle.

Aslam, M.↗

NASA NTRS1994

Application of Chlorine-Assisted Chemical Vapor Deposition of Diamond at Low Temperatures

Low temperature deposition of diamond has been achieved by a chlorine-assisted diamond chemical vapor deposition (CA-CVD) process. This method begins with the thermal dissociation of molecular chlorine into atomic chlorine in a resistively heated graphite furnace at temperatures between 1300 and 1500 deg. C. The atomic chlorine, upon mixing, subsequently reacts with molecular hydrogen and hydrocarbons. The rapid exchange reactions between the atomic chlorine, molecular hydrogen, and hydrocarbons give rise to the atomic hydrogen and carbon precursors required for diamond deposition. Homoepitaxial diamond growth on diamond substrates has been studied over the substrate temperature range of 100-950 C. It was found that the diamond growth rates are approximately 0.2 microns/hr in the temperature range between 102 and 300 C and that the growth rates do not decrease significantly with a decrease in substrate temperature. This is unique because the traditional diamond deposition using H2/CH4 systems usually disappears at substrate temperatures below approx. 500 deg. C. This opens up a possible route to the deposition of diamond on low-melting point materials such as aluminum and its alloys.

Pan, Chenyu↗

DOE OSTI2018

Mechanical design of thin-film diamond crystal mounting apparatus with optimized thermal contact and crystal strain for coherence preservation x-ray optics

A method and mechanical design for a thin-film diamond crystal mounting apparatus for coherence preservation x-ray optics with optimized thermal contact and minimized crystal strain are provided. The novel thin-film diamond crystal mounting apparatus mounts a thin-film diamond crystal supported by a thick chemical vapor deposition (CVD) diamond film spacer with a thickness slightly thicker than the thin-film diamond crystal, and two groups of thin film thermal conductors, such as thin CVD diamond film thermal conductor groups separated by the thick CVD diamond spacer. The two groups of thin CVD film thermal conductors provide thermal conducting interface media with the thin-film diamond crystal. A piezoelectric actuator is integrated into a flexural clamping mechanism generating clamping force from zero to an optimal level.

42 ENGINEERING↗

DOE OSTI2023

X-ray quantification of oxygen groups on diamond surfaces for quantum applications

Abstract Identifying the surface chemistry of diamond materials is increasingly important for device applications, especially quantum sensors. Oxygen-related termination species are widely used because they are naturally abundant, chemically stable, and compatible with stable nitrogen vacancy centres near the diamond surface. Diamond surfaces host a mixture of oxygen-related species, and the precise chemistry and relative coverage of different species can lead to dramatically different electronic properties, with direct consequences for near-surface quantum sensors. However, it is challenging to unambiguously identify the different groups or quantify the relative surface coverage. Here we show that a combination of x-ray absorption and photoelectron spectroscopies can be used to quantitatively identify the coverage of carbonyl functional groups on the { 100 } diamond surface. Using this method we reveal an unexpectedly high fraction of carbonyl groups ( > 9%) on a wide range of sample surfaces. Furthermore, through a combination of ab initio calculations and spectroscopic studies of engineered surfaces, we reveal unexpected complexities in the x-ray spectroscopy of oxygen terminated diamond surfaces. Of particular note, we find the binding energies of carbonyl-related groups on diamond differs significantly from other organic systems, likely resulting in previous misestimation of carbonyl fractions on diamond surfaces.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Extreme Enhancement-Mode Operation Accumulation Channel Hydrogen-Terminated Diamond FETs with V th < -6 V and High on-Current

In this work, a new Field Effect Transistor device concept based on hydrogen-terminated diamond (H-diamond) is demonstrated that operates in an Accumulation Channel rather than a Transfer Doping regime. The FET devices demonstrate both extreme enhancement-mode operation and high on-current with improved channel charge mobility compared to Transfer-Doped equivalents. Electron-beam evaporated Al 2 O 3 is used on H-diamond to suppress the Transfer Doping mechanism and produce an extremely high ungated channel resistance. A high-quality H-diamond surface with an unpinned Fermi level is crucially achieved, allowing for the formation of a high-density hole accumulation layer by gating the entire device channel which is encapsulated in dual-stacks of Al 2 O 3 . Completed devices with gate/channel length of 1 µm demonstrate record threshold voltage < -6 V with on-current > 80 mA mm -1 . Carrier density and mobility figures extracted by CV analysis indicate a high 2D charge density of ≈ 2 × 10 12 cm -2 and increased hole mobility of 110 cm 2 V -1 s -1 in comparison with more traditional Transfer-Doped H-diamond FETs. These results demonstrate the most negative threshold voltage yet reported for H-diamond FETs and highlight a powerful new strategy to greatly improve carrier mobility and enable enhanced high power and high frequency diamond transistor performance.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗