Nitrogen Impurity Concentration Research Articles

Fabrication and characterization of diamond (100) p+-i-n+ diodes with heavily nitrogen-doped films

N-type diamond-based diodes are currently faced with challenges associated with high contact resistance at the interface of the metal and n-type semiconductor. To address this issue, we attempt to reduce the contact resistance by utilizing a heavily nitrogen-doped film with a nitrogen impurity concentration of 8.0 × 1020/cm3. In the fabricated p+-i-n+ device, we observed a rectification ratio of six orders of magnitude at ±10 V and a built-in voltage of 3.5 V. These findings mark a significant milestone as they represent the first-ever report of room-temperature operation in a device that utilizes a heavily nitrogen-doped film as the n+-layer. This breakthrough has effectively overcome the high contact resistance in n-type diamond semiconductors. The implications of our findings are substantial, as they expand the potential of nitrogen in diamond power devices.

Enhanced Hall mobility in graphene-on-electronic-grade diamond

The outstanding electronic properties of graphene make this material a candidate for many applications, for instance, ultra-fast transistors. However, self-heating and especially the detrimental influence of available supporting substrates have impeded progress in this field. In this study, we fabricate graphene-diamond heterostructures by transferring graphene to an ultra-pure single-crystalline diamond substrate. Hall-effect measurements were conducted at 80 to 300 K on graphene Hall bars to investigate the charge transport properties in these devices. Enhanced hole mobility of 2750 cm2 V−1 s−1 could be observed at room-temperature when using diamond with reduced nitrogen (Ns0) impurity concentration. In addition, by electrostatically varying the carrier concentration, an upper limit for mobility is determined in the devices. The results are promising for enabling carbon–carbon (C-C) devices for room-temperature applications.

Effect of catalyst composition on growth and crack defects of large diamond single crystal under high temperature and pressure

Under the condition of 5.6 GPa and 1250–1450 ℃, the diamond single crystals are synthesized in a cubic anvil high-pressure and high-temperature apparatus. High-purity FeNiCo solvents or NiMnCo solvents are chosen as the catalysts. High-purity (99.99%) graphite powders selected as a carbon source. High-quality abrasive grade diamond single crystals with relatively developed (100) or (111) crystal planes are used as crystal seeds. The effects of catalyst composition on crack defects in diamond single crystals are studied carefully. Firstly, using FeNiCo and NiMnCo catalysts respectively, we carry out the diamond single crystal growth experiments. It is found that under the same crystal growth condition, the probability of crystal crack defects in diamond single crystals grown with FeNiCo catalyst is significantly higher than that of crystals grown with NiMnCo catalyst. We believe that this is related to the high viscosity, poor fluidity of FeNiCo catalyst melt, and the large specific surface area of the crystal during growth, which leads to its high requirements for the stability of growth conditions. Secondly, the relationship between the growth time and the limit weight gain speed of the diamond single crystal synthesized, respectively, by FeNiCo catalyst and NiMnCo catalyst are investigated. The results are shown below. 1) The limiting growth rate of diamond single crystal increases with the growth time going by. 2) In the same growth time, the limit growth rate of diamond crystal grown with NiMnCo catalyst is higher than that of diamond crystal grown with NiMnCo catalyst. Thirdly, by scanning electron microscopy (SEM), we calibrate the surface morphology of the synthesized diamond single crystal. The test results show that the diamond single crystal has a high surface flatness. Even for the crystals with crack defects in the interior, the surface flatness is still good. However, Fourier transform infrared (FTIR) measurements show that the nitrogen impurity content of diamond crystal grown by FeNiCo catalyst with crack defect is about 3.66×10<sup>–4</sup>. The content of nitrogen impurity in the crystal grown by NiMnCo catalyst without crack defect is about 4.88×10<sup>–4</sup>. The results show that there is no direct correlation between nitrogen impurity content and crack defects in diamond crystal.

Electrical and Structural Properties of Semi-Polar-ZnO/a-Al2O3 and Polar-ZnO/c-Al2O3 Films: A Comparative Study.

In this work, the properties of ZnO films of 100 nm thickness, grown using atomic layer deposition (ALD) on a-(100) and c-(001) oriented Al2O3 substrate are reported. The films were grown in the same growth conditions and parameters at six different growth temperatures (Tg) ranging from 100 °C to 300 °C. All as-grown and annealed films were found to be polycrystalline, highly (001) oriented for the c-Al2O3 and highly (101) oriented for the a-Al2O3 substrate. The manifestation of semi-polar-(101) and polar (001)-oriented ZnO films on the same substrate provided the opportunity for a comparative study in terms of the influence of polarization on the electrical and structural properties of ZnO films. It was found that the concentration of hydrogen, carbon, and nitrogen impurities in polar (001)-oriented films was considerably higher than in semi-polar (101)-oriented ZnO films. The study showed that when transparent conductive oxide applications were considered, the ZnO layers could be deposited at a temperature of about 160 °C, because, at this growth temperature, the high electrical conductivity was accompanied by surface smoothness in the nanometer scale. On the contrary, semi-polar (101)-oriented films might offer a perspective for obtaining p-type ZnO films, because the concentration of carbon and hydrogen impurities is considerably lower than in polar films.

Interaction mechanism of Ge, Ti, and N in diamond prepared by high pressure and high temperature conditions

In this paper, Ge-doped large single crystal diamond was synthesized under high pressure and high temperature (HPHT) conditions in NiMnCo-C and NiMnCo-Ti-C systems. The effects of Ge additives on the diamond morphology, nitrogen impurity content, and internal inclusions were investigated, and the interaction mechanism among germanium (Ge), nitrogen (N), and titanium (Ti) during the diamond growth process was discussed. The results show that the number of inclusions in diamond increase with increases in Ge addition in both systems. The N content of diamond grown in NiMnCo-C systems decreases with increases in Ge addition. However, Ge can more easily be doped into the diamond in a NiMnCo-Ti-C growth system. The experimental results show that the N can inhibit the amount of Ge entering the diamond lattice under HPHT conditions. When Ti was introduced into the system, it effectively removed N by combining with it, such that more Ge atoms could enter the diamond lattice.

Characteristics of diamond crystals from FeNiCo-C system with Ge doping under high pressure and high temperature

Various optical color centers in natural and synthetic diamond have attractive great attention of researched; to further investigate the effects of additive on diamond properties is of practical significance. In this work, diamond crystallization was investigated by temperature gradient growth method with Ge additive at a set pressure of 6.5 GPa and synthesis temperature ranging from 1290 to 1310 °C. Scanning electron microscope (SEM), and spectral characterization including Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL) spectra were used to investigate the surface growth mechanism of diamond. It was noticed that the visible inclusions gradually reduced in the as-grown diamond, accompanying with the increase of Ge additive in the synthesis cavity. The (111) surface of the synthesized diamond followed the layer growth pattern from the SEM results. According to the measured FTIR results, the nitrogen impurity concentration values of the synthesized diamond crystals decreased from 500 to 90 ppm, confirming that Ge showed its own ability to remove nitrogen impurity in the growth stage of diamond. Additionally, the nickel-related and nitrogen-related optical color centers of the obtained diamond were characterized by PL spectra. Characteristic peaks due to nickel-related optical color centers located at 515 or 535 nm, and Characteristic peaks attributing to nitrogen-related optical color centers located at 575 or 637 nm. We believe that the research is of great significance for the application of diamond in optical and quantum information science fields.

Study of MIS structures based on CdHgTe and HfO2 applied by PEALD

We investigate the HfO2/Hg0.78Cd0.22Te interface fabricated by plasma-enhanced atomic layer deposition (PEALD) at 120 °C During the deposition of HfO2, no donor-like defects are introduced into mercury cadmium telluride. X-ray photoelectron spectroscopy and ellipsometry were used to establish the optimal process regime at 120 °C and to demonstrate how HfO2 layer composition and growth rate per cycle depend on post-plasma purge time; the optimum is achieved at 6 s. Increasing the post-plasma purge time decreases the carbon and nitrogen impurity concentration in the HfO2 layer. Measurements of the admittance of metal-insulator-semiconductor (MIS) structures over the surface of a sample show that the electro-physical properties are uniform. We discuss the method of measuring the admittance of MIS structures that allows us to minimize the contribution of slow states with trapped charge on shape and shift of the C–V curve. The results demonstrate that the densities of fixed charge, slow states, and fast interfacial traps at the HfO2/MCT interface are greater than that for Al2O3/MCT (also formed by PEALD). The interface trap density is estimated from a normalized parallel conductance map, and the HfO2 film adheres well.

Hydrogen-terminated diamond MOSFETs on (0 0 1) single crystal diamond with state of the art high RF power density

Diamond field-effect transistor (FET) has great application potential for high frequency and high power electronic devices. In this work, diamond FETs were fabricated on (0 0 1) single crystal diamond with homoepitaxial layer. The nitrogen impurity content in the homoepitaxial layer is greatly decreased as measured by the Raman and photoluminescence spectra. The diamond field effect transistor with 100 nm Al2O3 as gate dielectric shows ohomic contact resistance of 35 Ω . mm, maximum drain saturation current density of 500 mA/mm, and maximum transconductance of 20.1 mS/mm. Due to the high quality of Al2O3 gate dielectric and single crystal diamond substrate, the drain work voltage of −58 V is achieved for the diamond FETs. A continuous wave output power density of 4.2 W/mm at 2 GHz is obtained. The output power densities at 4 and 10 GHz are also improved and achieve 3.1 and 1.7 W/mm, respectively. This work shows the application potential of single crystal diamond for high frequency and high power electronic devices.

Proximal nitrogen reduces the fluorescence quantum yield of nitrogen-vacancy centres in diamond

The nitrogen-vacancy colour centre in diamond is emerging as one of the most important solid-state quantum systems. It has applications to fields including high-precision sensing, quantum computing, single photon communication, metrology, nanoscale magnetic imaging and biosensing. For all of these applications, a high quantum yield of emitted photons is desirable. However, diamond samples engineered to have high densities of nitrogen-vacancy centres show levels of brightness varying significantly within single batches, or even within the same sample. Here we show that nearby nitrogen impurities quench emission of nitrogen-vacancy centres via non-radiative transitions, resulting in a reduced fluorescence quantum yield. We monitored the emission properties of nitrogen-vacancy centre ensembles from synthetic diamond samples with different concentrations of nitrogen impurities. All samples were irradiated with high energy electrons to create high densities of nitrogen-vacancy centres relative to the concentration of nitrogen impurities. While at low nitrogen densities of 1.81 ppm we measured a lifetime of 13.9 ns, we observed a strong reduction in lifetime with increasing nitrogen density. We measure a lifetime as low as 4.4 ns at a nitrogen density of 380 ppm. The change in lifetime matches a reduction in relative fluorescence quantum yield from 77.4% to 32% with an increase in nitrogen density from 88 ppm to 380 ppm, respectively. These results will inform the conditions required to optimise the properties of diamond crystals devices based on the fluorescence of nitrogen-vacancy centres. Furthermore, this work provides insights into the origin of inhomogeneities observed in high-density nitrogen-vacancy ensembles within diamonds and nanodiamonds.

PLACER DIAMONDS OF THE EASTERN AZOV REGION

The crystal morphology, photoluminescence behavior, nitrogen impurity concentrations and Raman spectra of diamonds from Quaternary alluvial deposits of the Eastern Azov region were studied. Macrodiamond from the Mius-Krynka river basin shown ideal rhombic dodecahedron habitus, and their geometric parameters are similar to those of rounded diamonds found in kimberlites and lamproites. The mantle temperature regime for the formation of Azovian diamonds was determined using infrared spectroscopy, the content and state of nitrogen impurities, and other defects in the crystals. Diamonds can be divided into different spectral types namely IaA, IaAB and IIa. They have low nitrogen contents from 19 to 491 ppm, with an average nitrogen content of 148 ppm and they have a relatively high degree of nitrogen aggregation (average value of % B = 33). Thermometric data for the Eastern Azov diamonds are in the range of 1097-1175 ºC for 2 billion years and 1120-1165 ºС for 3 billion years of crystals to stay in the mantle. N3, S1 and 575 nm centers are revealed in the photoluminescence spectroscopic measurements. The Raman shift for diamonds is in the range of 1331.0-1332.1 cm–1. The diamonds are probably associated with mantle eclogites, and they have been brought to Earth’s surface by kimberlites.

Mixed type Ib-IIa diamond from a Fe–Mg2Si3O8·5H2O–C system under high pressure and high temperature

The composition of the crystalline medium has an essential effect on the formation and properties of diamonds. Large single-crystal diamonds grown in a Fe–Mg2Si3O8·5H2O–C system by the temperature gradient method (TGM) at 5.8–6.3 GPa and 1400–1480 °C were investigated. It was found that as the Mg2Si3O8·5H2O content increased from 0 to 4 wt%, the synthesis pressure and temperature both increased, and more nitrogen-vacancy (NV) defect centers appeared in the diamond crystal. The nitrogen impurity concentration in type Ib diamonds synthesized in the pure FeC system was about 90 ppm, and the distribution of nitrogen impurities was uniform from core to rim. Furthermore, with a Mg2Si3O8·5H2O content of approximately 4.0 wt%, type Ib-IIa diamond was successfully synthesized. The infrared spectra (IR) results showed that the nitrogen content of the type Ib-IIa diamond was higher in the central zone of the crystal (79 ppm), decreased in the intermediate zone (42 ppm), and decreased further at the periphery (< 1 ppm). Thus, the type Ib-IIa diamond had significant heterogeneity in the distribution of nitrogen.

Wide bandgap tunability of N-alloyed ZnGa2O4 thin films

ZnGa2O4 films with different nitrogen impurity concentrations were deposited using radio frequency magnetron sputtering in an ammonia (NH3)/Ar gas mixture and were post-annealed at different temperatures, ranging from 600 °C to 900 °C, in NH3 atmosphere. The influence of ammonia partial pressure ratio and nitridation temperature on the microstructure, surface morphology, nitrogen doping profile, and optical properties has been investigated. The optical band gap of ZnGa2O4, under in-situ nitrogen-doping, decreases from 4.6 to 4.1 eV but the primitive ZnGa2O4 crystalline structure does not change. On nitridation, the optical band gap gradually decreases from 4.6 to 2.1 eV and the ZnGa2O4 changes into a zinc gallium oxynitride quaternary alloy structure. Secondary ion mass spectrometry analysis revealed that nitrogen atoms were uniformly distributed in the film. The narrowing, by more than 40%, of the optical band gap is attributed to the hybridization of Zn3d and N2p orbits promote p-d repulsion in the top of the valence band, and the formation of hexagonal wurtzite phase.

A review on forms and concentrations of nitrogen impurities in diamond

A review on forms and concentrations of nitrogen impurities in diamond

DIAMONDS OF UKRAINE: RESULTS AND GOALS

Diamonds from Ukraine were studied in terms of their separation into their geological and genetic types, distribution and occurrence, the ages of their host rocks, and their nature in Proterozoic and Neogene age sediments. The diamonds are variable in morphology, internal structure, concentration and degree of aggregation of nitrogen centers, carbon isotopes and mineral inclusions. Placer diamonds, primarily from Neogene sands, are anomalous in many respects. They are mostly extremely small, polyhedral, and morphologically diverse showing octahedral, rhombic dodecahedral and cubic forms and they have various colors. In addition to the large heterogeneity in nitrogen concentrations, many diamonds are characterized by a low degree of aggregation of nitrogen centers, which indicates short mantle residence times. Depending on the nitrogen impurity content, the degree of aggregation of nitrogen centers and the possible temperatures of crystallization, several types of diamonds are distinguished in the studied sedimentary placers. According to new isotope-geochemical data, placer diamonds are characterized by a wide range of carbon isotopic composition. This may indicate isotopic inhomogeneity of diamond carbon, different modes of formation and chemical variability in their source regions. Impact diamonds from meteorite craters and Neogene sedimentary deposits of Ukraine are paramorphoses from graphite with similar morphological, isotopic and structural characteristics. The goals of future research of Ukrainian diamonds are discussed.

Effects of Nitrogen Impurity Concentration on Nitrogen-Vacancy Center Formation in 4H-SiC

Spin defects of which states can be manipulated in Silicon Carbide (SiC) have drawn considerable attention because of their applications to quantum technologies. The single negatively-charged pairs of VSi and nitrogen atom (N) on an adjacent C site (NCVSi- center) in SiC is suitable for them. This paper reports the formation of NCVSi- centers on 4H-SiC epilayers with different nitrogen concentrations using light/heavy ion irradiation and subsequent thermal annealing. The formation of NCVSi- centers is characterized by the near infrared photoluminescence (PL) spectroscopy. It is shown that the PL intensity from NCVSi- centers depends on the N concentration and the ion irradiation conditions. The PL intensity increases monotonically with increasing the N concentration when the N concentration is above 2.6×1016 cm-3, whereas no linear correlation between them does not appear below that N concentration. Although the PL intensity increases with increasing defects induced by ion irradiation, the PL quenching due to neighboring residual defects appear at above the areal vacancy concentration of 1017 vac/cm2 and the broad Raman scattering spectra originated from vibration modes of amorphized regions hinder the PL from NCVSi- centers at above 1018 vac/cm2. The formation mechanism and the charge state stability of NCVSi- centers are discussed based on the obtained results.

Impurity Removal and Microstructural Analysis of Inconel 718 Refined by Hydrogen Plasma Arc Melting

The high-temperature melting and the removal of gaseous and metallic impurities from Inconel 718 by hydrogen plasma arc melting (HPAM) were investigated. Solid-type Inconel 718 scraps were used as raw material. The concentrations of oxygen, nitrogen, and metallic impurities in the scraps were simultaneously decreased by HPAM. The refined ingot satisfied the recommended criteria for commercial Inconel 718. Following the melting of Inconel 718 by HPAM, the microstructure of the as-cast depended on different parts of the ingots, due to the different cooling rate of each part.

Effect of sulfur on diamond growth and morphology in metal–carbon systems

Sulfur additives inhibit diamond crystallization in the Fe–Ni–C system at 6 GPa and 1400 °C and affect the diamond crystal morphology and nitrogen impurity content.

Impurity levels in cerium oxide microspheres prepared by internal gelation sol–gel methods

Impurity levels were measured in cerium oxide microspheres fabricated by modified internal gelation sol–gel methods. A combination of glow discharge mass spectrometry, electron impact mass spectrometry, combustion gas analysis, and instrumental gas analysis were used to assess a wide range of potential elemental impurities. Low concentrations of carbon, nitrogen, and hydrogen impurities in microspheres showed a dependence on how microspheres were washed. Silicon impurities are believed to derive from silicone oil used during sol–gel processing. Spheres washed by the preferred approach had impurity levels below 100 ppm for all elements tested. For applications such as nuclear fuels, sol–gel methods could meet purity specifications as long as metal nitrate feed solutions of sufficient purity are used and microspheres are washed appropriately. In this study, cerium was used as a surrogate for plutonium-238, which is used in radioisotope power systems as a heat source, to determine whether carbon or other impurities were concentrated during internal gelation processing and remained after heat treatments. Analyses indicated low concentrations of impurities in cerium oxide microspheres after sintering steps that were well below documented limits for plutonium-238 oxide fuels. Modified washing methods, combined with a pressurized water treatment, resulted in sintered cerium oxide sol–gel microspheres with low impurity levels.

Influence of nitrogen impurities on the characteristics of a patterned helium dielectric barrier discharge at atmospheric pressure

In this paper, a two-dimensional axisymmetric fluid model was established to investigate the influence of nitrogen impurity content on the discharge pattern and the relevant discharge characteristics in an atmosphere pressure helium dielectric barrier discharge (DBD). The results indicated that when the nitrogen content was increased from 1 to 100 ppm, the discharge pattern evolved from a concentric-ring pattern into a uniform pattern, and then returned to the concentric-ring pattern. In this process, the discharge mode at the current peak moment transformed from glow mode into Townsend mode, and then returned to glow mode. Further analyses revealed that with the increase of impurity level, the rate of Penning ionization at the pre-ionization stage increased at first and decreased afterwards, resulting in a similar evolution pattern of seed electron level. This evolution trend was believed to be resulted from the competition between the N2 partial pressure and the consumption rate of metastable species. Moreover, the discharge uniformity was found positively correlated with the spatial uniformity of seed electron density as well as the seed electron level. The reason for this correlation was explained by the reduction of radial electric field strength and the promotion of seed electron uniformity as pre-ionization level increases. The results obtained in this work may help better understand the pattern formation mechanism of atmospheric helium DBD under the variation of N2 impurity level, thereby providing a possible means of regulating the discharge performance in practical application scenarios.

Manifestation of diamond sectoriality during dissolution and graphitization

We studied the morphology of dissolution and graphitization forms of sectorial natural and synthetic diamonds. Experiments on diamond dissolution (graphitization) were performed in model systems of different composition in a wide range of temperatures and pressures. It was found that, after dissolution, the raised (positive) and etched (negative) regions of the relief are formed along the outcrops of the growth sectors on the round surface of the diamond crystals. The relief patterns associated with the sectorial structure of crystals do not affect in the geometry of dissolution forms, which is mainly determined by external factors such as solvent composition, redox conditions, and process temperature. Based on the relative height of the relief elements at the outcrops of different growth sectors, it is concluded that the rate of dissolution of the growth sectors of synthetic diamonds decreases in the sequence {1 0 0}, {1 1 1}, {3 1 1}, {1 1 0}. In graphitization, the highest graphitization rate is observed in the growth sectors of {1 0 0} faces as well. As a result, deep grooves are formed on the growth sectors {1 0 0} faces. We assume that the dissolution features of various growth sectors are determined by the dependence of the rate of diamond dissolution (graphitization) on the concentration of nitrogen impurities in the growth sectors of various simple forms.