Search

Surface charge transfer doping (SCTD) is an alternative approach to achieving n-type doped diamonds since the n-type bulk doping of diamonds remains a challenge, but so far efficient diamond n-type SCTD has not been achieved. Here we provide a comprehensive study of the n-type SCTD of the diamond by using first-principles calculations based on the density functional theory. Taking the principle that ionization potentials of the dopants must be higher than those of the diamond, we screened a series of molecules that may be suitable for diamond n-type SCTD doping. Methyl viologen and benzyl viologen provide the largest amount of transfer electron among the common n-type SCTD dopants for the oxygen and fluorine terminated (100) surface diamond, with the electron areal densities of 2.60 × 10 13 cm − 2 and 9.20 × 10 12 cm − 2 , respectively. It is indicated that the transferred electron amount is positively correlated with the difference between the ionization potentials of the dopants and the electron affinity of the diamond, while the density of dopants also has a positive impact with a decreasing trend. The present work provides a useful understanding of the physical mechanism for the n-type SCTD of diamonds, and benefits the development of n-type SCTD diamond materials. [ABSTRACT FROM AUTHOR]

Herein, a technological process for the fabrication of n‐type doped V‐shaped structures on (100) single‐crystalline diamond substrates, designed to overcome the limitations of n‐type doping on (100) surfaces, is presented. This doping enhancement process can be applied to realize electronic power devices such as a junction barrier Schottky diode or junction field effect transistors with low on‐resistance. Herein, a catalytic etching process is performed by using square‐shaped nickel masks on the diamond surface and annealing in a hydrogen atmosphere, resulting in the formation of inverted pyramidal structures with flat {111} sidewalls. The resulting V‐shaped structures are subsequently overgrown with phosphorus‐doped diamond to achieve n‐type doped facets with higher doping concentrations. Cathodoluminescence studies reveal the predominant incorporation of phosphorus donors on the {111} sidewalls of V‐shaped structures. [ABSTRACT FROM AUTHOR]

We report calculated energetics (at the GGA, and at the B3LYP, HSE06 hybrid density functional levels of theory) and electronic properties (B3LYP, HSE06) of Li and N co-doped diamond containing LiN x clusters (x = 1–4). Defect energies and structural properties at the GGA and hybrid (B3LYP, HSE06) levels of theory are very similar. Our results for isolated Li and N dopants agree with previous work in that they are not suitable candidates for shallow n-type donors. Here, we investigate the effects of addition of N atoms as a co-dopant with Li, which vary with the Li:N ratio and whether Li is interstitial or substitutional. Reaction energies, geometries, bonding and densities of states (DOS) are examined. Nitrogen stabilises substitutional rather than interstitial lithium. Atom-projected DOS show that the chief contributions to the defect states are not from orbitals on the dopant atoms themselves but from states associated with neighbouring carbon atoms. Only the tetrahedral 1:4 cluster, Li C N 4 , with substitutional Li is likely to behave as a shallow donor. We propose a non-molecular synthetic route for preparation of the Li C N 4 -doped material via prior generation of the N 4 V centre at temperatures at which Li is mobile but Li C N 4 clusters are not. Image 1 [ABSTRACT FROM AUTHOR]

To find potential n-type diamonds with shallow donor energy levels and low formation energies, the thermodynamic and electronic properties of Lithium-Boron (Li B) co-doped diamonds have been investigated using density functional theory (DFT) and hybrid density functional theory (HSE06). The structure, formation energy, electronic property and the potential synthesis pathway are analyzed. The results of the single Li defect is not a suitable candidate for a shallow n-type donor, as it distorts the diamond lattice and forms clusters, in agreement with previous work. The calculated ionization energy of Li i2 -B defect (0.29 eV) and the impurities formation energy (0.196 eV) is much lower than that of Li i defect. It suggests that the introduction of B helps improve the solubility of Li in diamond. Further structural analysis has shown that the incorporation of B atoms inhibits the diffusion of Li atoms and simultaneously reduces the internal strain in the diamond, resulting in a significant reduction in the distance between the two lithium atoms from 2.061 Å to 1.629 Å. At last, a non-molecular synthesis pathway of Li i2 -B co-doped diamond is proposed via prior generation of B-doped diamond at which Li atom is mobile which indicates there is a potential window-of-opportunity to prepare Li i2 -B co-doped diamond to achieve n-type diamond. [Display omitted] [ABSTRACT FROM AUTHOR]

For diamond with exceptional physical and chemical properties, it is a challenging task to develop an effective n -type dopant with satisfactory electronic properties. In this work, using the first-principles calculation, we report the n -type doping of diamond surface (areal electron density of 2.508 × 1013–4.090 × 1013 cm−2 and carrier mobility of 189–1186 cm2 V−1 s−1 at 298 K) by surface transfer doping using potassium (K). Electrons are transferred from the K atoms to the diamond surface, then electrons accumulation appears on the diamond surface. In addition, the areal electron density and electron affinity values increase with increasing K concentration. This work provides a new strategy for producing n -type diamond-based devices. [Display omitted] • Efficient surface n -type conductivity is obtained on diamond surface doped with K. • High areal electron density and carrier mobility at room temperature are achieved. • As the increase of K atoms, areal electron density and electron affinity increase. [ABSTRACT FROM AUTHOR]

The transfer length method (TLM) was used to investigate Ohmic contact properties using the tri-layer stack Ti/Pt/Au on a nitrogen-doped n-type conducting nanocarbon (nanoC) layer grown on a diamond (100) substrate. Room temperature electrical measurements were taken, and samples were annealed to observe changes in electrical conductivity. Low specific contact resistivity values between the electrode and nanoC layer of 8 × 10−5 Ωcm2 were achieved, which is almost two orders of magnitude lower than previously reported values. The results were attributed to the increased nitrogen incorporation, and the presence of electrically active defects which leads to an increase in conduction in the nanocarbon film. [Display omitted] • New nanocarbon growth with high nitrogen incorporation • XRD and Raman showed mixture of amorphous and crystalline phases. • Ti/Pt/Au contacts had Ohmic properties. • The lowest contact resistivity was measured at ∼8E-5 Ωcm 2 . [ABSTRACT FROM AUTHOR]

The Lithium-doped and Lithium-Boron (Li-B) co-doped diamonds were investigated by density functional theory to find out potential shallow donor impurities in diamond. In Li doped diamond, only interstitial Li doped diamond shows an effective n-type property with a low ionization energy of 0.04 eV. However, an extremely low solubility was found in diamond. In order to overcome this obstacle, co-doping with boron exhibits a unique advantage. A comprehensive research of different Li-B co-doping structures was conducted. With the help of B atom, the solubility of Li is greatly improved. Moreover, through first-principles calculations, we found for the first time that Li i2 -B co-doped diamond has both low formation energy (−6.17 eV) and low ionization energy (0.29 eV). The 2p states of B and 2s states of Li dominate the conduction band minimum (CBM). Li atoms have many adsorption sites on intrinsic and B doped (001) surface of diamond, among which the bridge site of the dimer chain is the most suitable adsorption site for Li. It suggests that through the addition of B, Li i2 -B co-doping can be an up-and coming candidate of effective shallow donor impurity in diamond. [Display omitted] [ABSTRACT FROM AUTHOR]

High concentrations of lithium (~5×1019 cm−3) and nitrogen (~3×1020 cm−3) have been simultaneously incorporated into single-crystal and microcrystalline diamond films using Li3N and gaseous ammonia as the sources of Li and N, respectively. Using sequential deposition methods, well-defined localised layers of Li:N-doped diamond with a depth spread of less than ±200nm have been created within the diamond. The variation in Li:N content and amount of diffusion within the various types of diamond suggests a model whereby these atoms can migrate readily through the grain-boundary network, but do not migrate much within the grains themselves where the diffusion rate is much slower. However, the high electrical resistivity of the doped films, despite the high Li and N concentrations, suggests that much of the Li and N are trapped as electrically inactive species. [ABSTRACT FROM AUTHOR]

Abstract: The shallow n-type doping of boron doped diamond with an excess of deuterium has attracted considerable attention. However, despite numerous studies, the nature of this donor is the subject of continued debate. We show that possesses a substantial number of metastable states, which are likely to play a role in the properties of the defect, and that it is possible in principle for these higher energy metastable structures to be reached. The levels induced by these metastable defects are shown to be shallower than the original deep levels, but still deeper than the experimentally observed donor levels. We also report spin density distributions of centres, which may be compared with experiment, towards establishing the nature of the new donor. [Copyright &y& Elsevier]

Abstract: The microwave plasma-assisted deposition of reproducible and homogeneously n-type phosphorus-doped polycrystalline (microcrystalline) diamond films on silicon substrates is described. The phosphorus incorporation is obtained by adding gaseous phosphine (PH3) to the gas mixture during growth. The low CH4/H2 ratio (0.15%) and the use of the same growth parameters as for homoepitaxial {111} films, led to a good crystalline quality of the continuous polycrystalline diamond layers, confirmed by SEM images and Raman spectroscopy measurements. Secondary-ion mass spectrometry (SIMS) analysis measured a phosphorus concentration [P] of at least 7×1017 cm−3. Cathodoluminescence spectroscopy in our P-doped polycrystalline films shows a phosphorus bound exciton (BETO P) peak between 5.142 and 5.181 eV. Cathodoluminescence and Raman-effect spectroscopy confirmed the improvement of the crystalline quality of our films as well as a decrease in the intensity of the internal strain when the grain size was decreased. Cathodoluminescence imaging and SIMS depth profile of phosphorus demonstrated a very good homogeneity of phosphorus incorporation in the films. [Copyright &y& Elsevier]

Abstract: Although diamond has been successfully n-type doped with phosphorus, the search for shallower n-type dopants in diamond has continued. Interstitial Li and Na have been predicted to be shallow donors, however, experimental results have been contradictory. Aluminum, if incorporated, may be expected to form an acceptor in the same way as boron, and it too was modeled here. We report ab initio Density Functional Theory modeling of Li, Na and Al in diamond and show that although interstitial lithium and sodium are shallow donors, interstitial Li will readily diffuse and that it is favorable for migrating Li to be trapped at vacancies. The resulting substitutional Li is not only passivated but also compensates remaining interstitial donors, explaining the high resistivity or electrical inactivity observed in Li doped diamond. Na is shown to be most stable as a substitutional acceptor, in agreement with Na diffusing as a negative ion in diamond. Substitutional aluminum is found to induce a deep acceptor level in the band gap, much deeper than the boron acceptor level, inducing greater distortion of the host lattice. [Copyright &y& Elsevier]

We present the results of density functional calculations of donor and acceptor characteristics of defects in diamond. We compare different computational approaches and relate the calculations to experimental data where available. We find that the best method appears to be comparing levels of the defects with some known reference state. Furthermore, a number of pnictogen and chalcogen–hydrogen defects have shallow donor qualities, and we comment on the electrical levels of boron–hydrogen complexes potentially present in p-type CVD diamond. [Copyright &y& Elsevier]

The cold-implantation rapid annealing (CIRA) routine was used to treat diamonds with B+-, C+-, N+- and O+-ions, respectively. Implantations were done at liquid nitrogen temperature and the subsequent rapid thermal anneals (RTAs) were done to only 400 °C. The ion doses were chosen to ensure that the radiation damage introduced would be the same irrespective of the ion implanted. The resultant electrical resistance behaviour was measured for isothermal anneals at 400 °C, followed by isochronal anneals at higher temperatures. The results can be explained consistently by postulating that acceptors, situated at ≈0.37 eV, had been activated in the B+-ion treated diamonds, and that donor states, situated at ≈0.32 and 0.28 eV, had been generated in the O+- and N+-treated diamonds, respectively. Hysteresis effects measured during heating and cooling of the diamonds are ascribed to the presence of ND1-defects (negative vacancies), but it is concluded that, contrary to previous assumptions, the formation of these defects may not be the primary mechanism by which shallow donors are compensated. [Copyright &y& Elsevier]

We present ab initio energetics of sulfur (S)–hydrogen (H) complex defects in diamond. If the defects are in partial equilibrium with the dopants adsorbed on the restored (100) surface, some S–H complexes may be incorporated with less energy costs than that required for single vacancy (V) formation. However, they do not exhibit shallow donor characters. Thus, it is not quite obvious whether the S atoms doped in diamond can work as real donors. [Copyright &y& Elsevier]

The lithium-doped (Li-doped) diamond and lithium‑nitrogen (Li N) co-doped diamond at different structures were investigated by the first-principles density functional theory to explore the possibility to achieve effective and shallow donors in diamond. Although the ionization energy of interstitial Li-doped diamond is low, its high formation energy shows that Li could be insoluble in diamond. However, the formation energy of Li N co-doped diamond decreases with increasing the number of N atoms around the Li atom. We found, for the first time, the formation energies of Li N 4 and Li N 3 co-doped diamond are negative, indicating that the doping efficiency of Li in diamond could be improved by introducing N atoms. Furthermore, we demonstrated that the ionization energy of Li N 4 is quite low for n-type doping. The N-2s states and Li-s states are responsible for the conduction band edge of Li N 4 co-doped diamond. As a result, the Li N 4 could be expected as an alternative shallow donor impurity in diamond. Unlabelled Image • We found the formation energy of Li-N co-doped diamond could decrease with increasing the number of N atoms around the Li atom. Especially, we found, for the first time the formation energies of Li-N4 co-doped diamond are negative, indicating that the doping efficiency of Li in diamond could be improved by introducing N atoms. • We demonstrated the ionization energy of Li-N4 is quite low for n-type doping. The results suggest that Li-N4 co-doping diamond have great potential to achieve n-type conductivity in experimental. • We found, for the first time, there exists a barrier energy of 1.96eV during the formation process of Li-N4 structure, which may explain why Li-N4 structure is difficult to achieve in the experiment. [ABSTRACT FROM AUTHOR]