This work studies the correlation between mean retardance and thickness of diamond substrates grown homoepitaxially via microwave plasma-enhanced chemical vapor deposition (MPCVD). We measure the retardance of a diamond substrate in two orientations: perpendicular and parallel to the growth direction. Our experimental results demonstrate that the correlation between mean retardance and thickness differs for these orientations. When measured perpendicular to the growth direction, the mean retardance is approximately proportional to the square root of the substrate thickness. In contrast, when measured parallel to the growth direction, we observe a generally higher mean retardance and an approximately linear correlation with thickness. This anisotropy arises not from differences in stress magnitude but from differences in the interlayer correlation of the principal stress axes, as evidenced by correlation coefficients between the azimuth angles of consecutive layers in the diamond crystal. To simulate the integrated retardance of diamond wafers, we propose a two-dimensional random walk model with momentum drift, which captures the diamond crystal tendency to preserve the azimuth angle across the samples. By optimizing the momentum factor, we show that the model can closely match experimental data. The momentum factor is found higher along the growth direction, which is consistent with the calculated correlation coefficients. Furthermore, both the model and experiments indicate that retardance-to-thickness ratios of thin samples converge toward similar base retardances in both orientations. These findings establish a quantitative framework for interpreting birefringence in diamond substrates, with implications for material selection and development in thermal management, quantum sensing, high-power electronics, and optical applications.

In this systematic study, it was demonstrated that varying the UV generated ozone exposure time of the diamond surface during fabrication enabled Schottky barrier height tuning on the order of 0.1 eV using Mo and Ti contacts to diamond, with the potential for finer adjustments. The Schottky barrier height (SBH) could be controlled from 1.61 +/- 0.03 to 1.98 +/- 0.02 eV for Mo and 1.35 +/- 0.05 to 1.77 +/- 0.05 eV for Ti at room temperature by varying the exposure time from 0 to 50 min. The fabricated Schottky barrier diodes achieved high rectification ratios on the order of 1011. Following 573 K high temperature exposure, the apparent SBH was found to decrease and become increasingly indistinguishable at room temperature among different UV ozone treatment times. However, the temperature dependence of the forward current voltage curves up to 523 K revealed the presence of barrier inhomogeneity and revealed that the average SBH and degree of inhomogeneity increased with higher UV ozone treatment times. Thus, the use of the conventional Richardson plot often used to determine the effective SBH can underestimate the value when barrier inhomogeneity is present. In the reverse bias, the suppression of leakage current due to increased Schottky barrier heights in accordance with thermionic emission and thermionic field emission theory was demonstrated at high temperatures and further supported the need for an inhomogeneity model to extract a constant average SBH in the diamond diodes.

Low-resistance Ohmic contacts are necessary for high-performance electronic devices. Ultrawide-bandgap semiconductor materials typically have high-resistance Ohmic contacts between the metal contact and the semiconductor. For single-crystal boron-doped diamond, with a bandgap of 5.5 eV, the reported specific contact resistance values vary from >10(-3) Omega cm(2) to the lowest reported value of 2 x 10(-7) Omega cm(2). To obtain this low-resistance Ohmic contact, a high temperature, >500 degrees C, annealing is usually required, which can limit fabrication procedures and compromise device designs. On p-type single-crystal diamond, the lowest reported contact resistance is 0.39 Omega mm. This article reports specific contact resistances of 8.2 x 10(-8) to 3.6 x 10(-7) Omega cm(2) and contact resistances 0.027 to 0.041 Omega mm, which are significantly better than reports in the literature and are achieved without the annealing step. The results are achieved by reactive ion etching 10 to 20 nm into the boron-doped diamond surface. After the etch, evaporated Ti/Au forms Ohmic contacts with resistances between 0.08 and 0.2 Omega mm without an anneal. An additional step of exposing the etched surface to an intense H-2 plasma at 700 degrees C before Ti/Au deposition, results in Ohmic contacts between 0.027 and 0.041 Omega mm.

For single crystal diamond (SCD) to gain practical use in technical applications including solid state electronics, thin (<1 μm), doped epitaxial SCD layers with very low (<1 nm) surface roughness are required. Conventional SCD chemical mechanical polishing (CMP) processes are insufficient to meet the requirements of such applications because the material removal rate (MRR) is often characterized inappropriately, and the material removal uniformity is seldom considered. In this study, chemical vapor deposition (CVD) growth of two lightly boron doped (p-) epilayers was performed on 3misoriented (100) high pressure high temperature substrates of 4.5 x 4.5 mm2 area. A subsequent 8-hour oxidative CMP process utilizing potassium permanganate and a novel self-leveling holder design decreased the average surface roughness from 3.83 nm and 1.57 nm to 0.20 nm and 0.16 nm for the two samples, respectively. MRRs were determined by evaluating five circular wear monitor structures in each sample by atomic force microscopy before and after the CMP process. The average MRRs were found to be 38.6 nm/hr and 37.3 nm/hr for the two samples. The purpose of this study is to demonstrate a CMP process suitable for polishing thin SCD epilayers to meet the needs of solid-state electronics applications.

The potential of diamond for electronic materials can be realized by creating well-controlled p- or n-type doping profiles. p-type doping is achieved by ion implantation of boron followed by high temperature annealing to relax the lattice, reduce the defects and create active dopant sites by allowing diffusion of defects in the diamond crystal. It has been found that even after this diffusion the percentage of active dopant sites after high temperature annealing are only a small fraction of the total doping. We perform first principles density functional theory calculations and estimate the migration barrier energy (MBE) for diffusion of carbon vacancies, hydrogen, boron and their complexes in diamond including the boron‑carbon vacancy complex which was recently observed and predicted as a color center for qubit realization. These defects are commonly found after ion implantation of boron in diamond. Here, we use nudged elastic band (NEB) technique to estimate the MBE for these defects and use it to predict the corresponding annealing temperature. Our calculations correctly predict the MBE for carbon vacancy as compared to the available references in literature and extend the calculation to other defects predicted in ion implanted diamond. Our objective of evaluating the MBE is to predict the diffusion processes occurring during post-implantation annealing of diamond.

The efficacy of oxygen (O) surface terminations on diamond is an important factor for the performance and stability for diamond-based quantum sensors and electronics. Given the wide breadth of O-termination techniques, it can be difficult to discern which method would yield the highest and most consistent O coverage. Furthermore, the interpretation of surface characterization techniques is complicated by surface morphology and purity, which if not accounted for will yield inconsistent determination of the oxygen coverage. We present a comprehensive approach to consistently prepare and analyze oxygen termination of surfaces on (100) single-crystalline diamond. We report on x-ray photoelectron spectroscopy (XPS) characterization of diamond surfaces treated with six oxidation methods that include various wet chemical oxidation techniques, photochemical oxidation with UV illumination, and steam oxidation using atomic layer deposition (ALD). Our analysis entails a rigorous XPS peak-fitting procedure for measuring the functionalization of O-terminated diamond. The findings herein have provided molecular-level insights on oxidized surfaces in (100) diamond, including the demonstration of clear correlation between the measured oxygen atomic percentage and the presence of molecular contaminants containing nitrogen, silicon, and sulfur. We also provide a comparison of the sp ^2 carbon content with the O1s atomic percentage and discern a correlation with the diamond samples treated with dry oxidation which eventually tapers off at a max O1s atomic percentage value of 7.09 ± 0.40%. Given these results, we conclude that the dry oxidation methods yield some of the highest oxygen amounts, with the ALD water vapor technique proving to be the cleanest technique out of all the oxidation methods explored in this work.

Thick diamond films are needed for high power device applications. One approach is to grow via the step-flow growth mode on miscut substrates. In this paper we correlate variations of surface morphology and optical properties of a 250 μm-thick undoped diamond layer, grown at a rate of 10.4 μm/h, on a (001) diamond substrate with a miscut angle of 10 degrees towards a <010> direction. The epilayer surface comprises regions with island growth on (001) planes, and regions parallel to the miscut substrate surface exhibiting step-bunching and faceting and resulting in various degrees of surface roughness. The optical properties exhibit a combination of sharp and broad luminescence peaks, which are found to be specific to growth morphology and to the nitrogen content in the near-surface region.

Diamond is one of the most promising semiconductor materials for high power applications because of its exceptional electronic and thermal properties. Diamond bipolar devices are promising for ultra-high voltage applications (>10kV), but diamond PN junctions have limitations due to (1) a high turn-on voltage (∼5V) giving a significant on-state voltage drop and (2) n-type diamond having higher resistivity and poor ohmic contacts. To address this problem, the implementation of an alternative n-type UWBG semiconductors with shallow donor dopants should be considered. $\beta$ -Gallium Oxide ( $\beta$ -Ga 2 O 3 ) is a semiconductor that has gained significant attention due to its attractive properties like its wide bandgap (4.85eV), good n-type doping, and high breakdown field in the range of 8 MV/cm. Diamond's outstanding thermal properties can serve as a heat dissipater at high power operations, which can compensate for the poor thermal conductivity of $\beta$ -Ga 2 O 3 . This study formed p-type diamond and n-type Ga 2 O 3 heterojunction diodes and measured their electrical characteristics. TCAD simulations of the pn junction were performed to further understand the current conduction.

Journal Article Exploring the Effect of Diffraction Conditions on Off-Axis Phonon EELS Get access Yifan Wang, Yifan Wang School for Engineering of Matter, Transport & Energy, Arizona State University, Tempe, AZ, United States Corresponding author: ywan1240@asu.edu Search for other works by this author on: Oxford Academic Google Scholar Shize Yang, Shize Yang Eyring Materials Center, Arizona State University, Tempe, AZ, United States Search for other works by this author on: Oxford Academic Google Scholar Alec Fischer, Alec Fischer Department of Physics, Arizona State University, Tempe, AZ, United States Search for other works by this author on: Oxford Academic Google Scholar Timothy Grotjohn, Timothy Grotjohn Department of Electrical & Computer Engineering, Michigan State University, East Lansing, MI, United StatesFraunhofer USA Center Midwest, Michigan State University, East Lansing, MI, United States Search for other works by this author on: Oxford Academic Google Scholar Fernando Ponce, Fernando Ponce Department of Physics, Arizona State University, Tempe, AZ, United States Search for other works by this author on: Oxford Academic Google Scholar Peter A Crozier Peter A Crozier School for Engineering of Matter, Transport & Energy, Arizona State University, Tempe, AZ, United States Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 653–655, https://doi.org/10.1093/micmic/ozad067.320 Published: 22 July 2023

Single‐crystalline inorganic semiconductor nanomembranes (NMs) have attracted great attention over the last decade, which poses great advantages to complex device integration. Applications in heterogeneous electronics and flexible electronics have been demonstrated with various semiconductor nanomembranes. Single‐crystalline aluminum nitride (AlN), as an ultrawide‐bandgap semiconductor with great potential in applications such as high‐power electronics has not been demonstrated in its NM forms. This very first report demonstrates the creation, transfer‐printing, and characteristics of the high‐quality single‐crystalline AlN NMs. This work successfully transfers the AlN NMs onto various foreign substrates. The crystalline quality of the NMs has been characterized by a broad range of techniques before and after the transfer‐printing and no degradation in crystal quality has been observed. Interestingly, a partial relaxation of the tensile stress has been observed when comparing the original as‐grown AlN epi and the transferred AlN NMs. In addition, the transferred AlN NMs exhibits the presence of piezoelectricity at the nanoscale, as confirmed by piezoelectric force microscopy. This work also comments on the advantages and the challenges of the approach. Potentially, the novel approach opens a viable path for the development of the AlN‐based heterogeneous integration and future novel electronics and optoelectronics.

We report the results of the investigation of bulk and surface acoustic phonons in the undoped and boron-doped single-crystal diamond films using the Brillouin-Mandelstam light scattering spectroscopy. The evolution of the optical phonons in the same set of samples was monitored with Raman spectroscopy. It was found that the frequency and the group velocity of acoustic phonons decrease nonmonotonically with the increasing boron doping concentration, revealing pronounced phonon softening. The change in the velocity of the shear-horizontal and the high-frequency pseudo-longitudinal acoustic phonons in the degenerately doped diamond, as compared to that in the undoped diamond, was as large as ∼15% and ∼12%, respectively. As a result of boron doping, the velocity of the bulk longitudinal and transverse acoustic phonons decreased correspondingly. The frequency of the optical phonons was unaffected at low boron concentration but experienced a strong decrease at the high doping level. The density-functional-theory calculations of the phonon band structure for the pristine and highly doped samples confirm the phonon softening as a result of boron doping in diamond. The obtained results have important implications for thermal transport in heavily doped diamond, which is a promising material for ultra-wide-band-gap electronics.

This work focuses on the unique potential of high-power, high-frequency frequency multipliers using diamond Schottky Barrier Diodes (SBDs). We demonstrate the design, fabrication, and small-signal RF characterization of doublers on single-crystalline diamond (SCD). This is the first attempt to realize a frequency multiplier fully integrated on diamond. The SBDs utilized are developed on a p − /p + boron-doped SCD wafer. The fabricated structures are compact, occupying an area smaller than 10 mm 2 each. Small-signal RF measurements are performed from 50 MHz up to 67 GHz. The results of this initial attempt are very promising for future high-power MMIC multiplier structures for microwave and mm-wave frequencies.

Diamond is a highly attractive ultrawide bandgap semiconductor for next-generation high-power switching devices and RF devices for its superior physical and electrical properties. However, the lack of effective n-type dopants in diamond has limited the material to only unipolar p-type device applications. Heterostructure bipolar devices that use better n-type semiconductors together with p-type diamond is an approach to get high performance devices. In this work, p–n–p AlGaAs/GaAs/diamond heterojunction bipolar transistors (HBTs) are proposed and fabricated using a grafting technique. The double-heterojunction is formed by transferring an AlGaAs(p-type)/GaAs(n-type) membrane onto single-crystalline p-type doped diamond with an electron affinity of 0.32 eV. The epitaxial AlGaAs/GaAs emitter-base p–n junction shows an ideality factor of 1.09 with an Ion/Ioff of 1.53 × 107 at ± 1.5 V. The grafted GaAs/diamond n–p junction shows an ideality factor of 3.67 with an Ion/Ioff of 3.74 × 1010 at ± 5.2 V. Due to the valence-band energy barrier of 0.3 eV between the GaAs base and the diamond collector, the measured current gain for the HBT is slightly below unity. Simulations show that by reducing the electron affinity value of the p-type diamond, the base-collector energy barrier height can be correspondingly reduced, and high current gain can be expected.

This paper demonstrates the design, fabrication, and RF testing of a monolithic lowpass filter (LPF) on single-crystalline diamond (SCD). This is the first time an RF filter has been fabricated on SCD. The LPF consists of grounded coplanar waveguide (GCPW) and microstrip (MS) transmission lines, via-less GCPW-to-MS transitions, and a bottom ground plane, all printed on a 5 mm × 5 mm × 0.15 mm SCD wafer with Aerosol Jet Printing technology using silver ink. The LPF is a stepped-impedance filter designed to have a cutoff frequency of 40 GHz and was measured from 10 MHz up to 67 GHz. Our results indicate that SCD is a good platform for the realization of high-frequency RF structures on a single substrate using additive manufacturing techniques.

This paper demonstrates the fabrication process and RF testing of a monolithic Wilkinson power divider (WPD) on single-crystalline diamond (SCD). The Grounded Coplanar Waveguide (GCPW) and microstrip (MS) transmission lines (TLs), the via-less GCPW-to-MS transitions, and the ground plane in the WPD configuration are printed on a 5×5 mm2 SCD wafer with the Aerosol Jet Printing (AJP) technique using silver ink. The resistor is fabricated via a combination of thin-film process and standard photolithography using nickel chromium (NiCr). Our results show good RF performance from 22 up to 40 GHz, indicating that SCD is a good platform for the integration of high-power and high-frequency electronics on a single substrate using additive manufacturing techniques.

This work focuses on the unique high-frequency power-handling capabilities of diamond Schottky Barrier Diodes (SBDs). We demonstrate the design, fabrication, and large-signal RF characterization, via active Load/Source-Pull (L/S-P), of a SBD on single-crystalline diamond (SCD). This is the first time a fully-integrated RF SBD has been fabricated and characterized via high-power impedance matching. The SBD was developed on a p(-)/p(+) boron-doped SCD wafer. Active L/S-P was performed at 10 GHz for an input power (P-in) of 34 dBm, attaining an output power (P-out) of 333 dBm, yielding a loss of 0.7 dB under matching conditions and an RF power density of similar to 375 W/mm(2). These RF power levels are higher than those available in the literature for SBDs and show that diode large-signal characterization via active L-P can potentially play a significant role in the design of multipliers, rectifiers, and detectors that aim to deliver high P-out without thermal degradation.

A commercial viable solid-state direct current circuit breaker with fast switching performance for the use in the 1-100kV range requires a low loss on-resistance close to commercial available mechanical breakers [1]. Diamond provides excellent semiconductor properties for those breaker applications with a material characteristics superior in high electric field breakdown strength, higher thermal conductivity, and high charge carrier mobility as compared to silicon, silicon carbide, and gallium nitride [2-4]. These properties will enable diamond electronic devices that will be more energy efficient while keeping the active area of devices to lower values, which offers a potential cost advantage in case of a better availability of large-area substrates [5,6]. Diamond diodes [7-9], diamond field effect transistors [10], and gate turn-off thyristor devices [11-13] are proposed to be the core unit in a medium voltage direct current (MVDC) solid-state circuit breaker [14,15]. A reduced energy loss in solid-state breakers by using diamond will enable a competitive placement of diamond breakers on the MVDC market with a decisive advantage of a much faster response to electrical circuit faults and more robust DC electrical energy delivery systems with >1MW capacity. The diamond-based diode and FET development focuses on devices in the 1-5kV range and the diamond thyristors cover a 15-20kV range. Higher voltages would ultimately be achieved with series circuit arrangements of the diamond devices. Diamond offers also excellent properties for applications in the biomedical sector [16]. The manufacturing of tailored biopharmaceuticals, stem cells, or human tissue is being attempted through the utilization of single-use perfusion bioreactors due to its minimal spacial and financial costs, and its ability to execute critical parallel processing methods [17,18]. However, continuous monitoring of analytes in multifaceted protein mixtures and achieving full automation of production are challenges inhibiting commercialization of tailored products to a reasonable price. Constant and instantaneous monitoring of a bioreactor both ensures flexibility with the opportunity for quick adjustments and eliminates contamination risks from manual sampling. Also, it is essential that the bioactive layer of an integrated biosensor monitoring system sustains the lifetime of the processing cycle, as well as display a shelf life compatible with standard inventory consumption. Achieving and maintaining the specific conditions necessary to produce complex bio-products requires a robust real-time monitoring with redundancy and automated control of a variety of nutrients, intermediate metabolites, and cell products within the bioreactor. Diamond biosensors exhibit low biofouling rates and show promising results in the in-situ monitoring of the bioprocess conditions for the full operation time of single-use bioreactors [19]. Operational human IL-8 antibodies have been successfully adhered to the diamond sensor surface [20]. A high antibody concentration and activity as a measure of biosensor sensitivity is obtained using a modified ELISA procedure. The results indicate a reasonable robust diamond biosensor performance suitable for in-situ applications in the complex environment of bioreactors [21]. Song, C. Peng, A.Q. Huang (2017) IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS 5(1), 278. Kalish (2007) Journal of Physics D: Applied Physics 40(20), 6467. Hiraiwa, H. Kawarada (2013) Journal of Applied Physics 114(3), 034506. Tsao et.al. (2018) Advanced Electronic Materials 4(1), 1600501. Friel et.al. (2019) Diamond and Related Materials 18, 808. Tallaire, J. Achard, F. Silva, O. Brinza, A. Gicquel (2013) Comptes Rendus Physique 14, 169. Alvearez, M. Boutchich, J. P. Kleider, T. Teraji, Y. Koide (2014) J. Phys. D: Appl. Phys. 47, 355102. Ozawa et.al. (2018) Diamond and Related Materials 85, 49. Zimmermann et.al. (2005) Diamond & Related Materials 14(3-7), 416. Huang, B. Zhang (2000) Solid-State Electronics 44, 325. Paques et.al. (2011) IEEE Electron Device Letters 32, 1421. HERLET, K. RAITHEL (1966) Solid-State Electronics 9, 1089. ADLER (1978) IEEE TRANSACTIONS ON ELECTRON DEVICES ED-25(1), 16. Shenai (2018) IEEE TRANSACTIONS ON ELECTRON DEVICES 65(10), 4216. Gu, P. Wheeler, A. Castellazzi, A.J. Watson, F. Effah (2017) Energies 10, 495. Hébert, S. Ruffinatto, P. Bergonzo (2015) Carbon for Sensing Devices, 978-3-319-08648-4, 227. Shukla, U. Gottschalk (2013) Trends in Biotechnology 31(3), 147. Bijonowski, W.M. Miller, J.A. Wertheim (2013) Current Opinion in Chemical Engineering 2(1), 32. Bixler, B. Bhushan (2012) Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, 2381. Navas et.al. (2018) Applied Surface Science 433, 408. Mross, T. Zimmermann, N. Winkin, M. Kraft, H. Vogt (2016) Sensors and Actuators B: Chemical 236, 937.

Despite the deep dopant level, diamond field effect transistors (FET) are expected to outperform SiC FET on critical aspects such as breakdown voltage, on-resistance, and power loss at elevated temperatures. Among diamond FET devices, hydrogen-terminated diamond FETs based on surface transfer doping has attracted most of the interest due to its high current capability. However, maintaining the stability of the hydrogen termination and the induced 2D hole gas has been challenging. Most hydrogen-terminated diamond FETs are not recommended to operate at temperatures higher than 400 °C even with the surface passivation [1]. In this study, we successfully fabricated a lateral, p-type conducting layer, diamond metal-semiconductor FET and demonstrated its performance at elevated temperatures up to 430 °C despite the fact that the transistors during the measurements were exposed to air with no passivation.

In low-pressure capacitively coupled discharges, a heating mode transition from a pressure-heating dominated state to an Ohmic-heating dominated state is known by applying a small transverse magnetic field. Here we demonstrate via particle-in-cell simulations and a moment analysis of the Boltzmann equation that the enhancement of Ohmic heating is induced by the Hall current in the E x B direction. As the magnetic field increases, the Ohmic heating in the E x B direction dominates the total electron power absorption. The Ohmic heating induced by the Hall current can be well approximated from the Ohmic heating of unmagnetized capacitively coupled discharges.

We demonstrated GaAs/diamond (GaAs-C-sp3)np diodes via lattice-mismatched semiconductor grafting: forming heterostructures with an ultrathin oxide (UO) layer at the interface. High-performance rectifying characteristics were measured from the GaAs/C-sp3 diodes with sharp reverse breakdown voltage (V-b) of -44.5 V. Capacitance-voltage (CV) measurements were carried out and the measurement results were used to construct the band diagram of the pn junction. Furthermore, an AlGaAs/GaAs/C-sp3 pnp structure was fabricated and both junctions were characterized for their I-V characteristics. The results show the prospect of realization of pnp AlGaAs/GaAs/C-sp3 HBTs in the future.