Wide bandgap dielectrics are attractive materials for the fabrication of photonic devices because they allow broadband optical operation and do not suffer from free-carrier absorption. Here we show that polycrystalline diamond thin films deposited by chemical vapor deposition provide a promising platform for the realization of large scale integrated photonic circuits. We present a full suite of photonic components required for the investigation of on-chip devices, including input grating couplers, millimeter long nanophotonic waveguides and microcavities. In microring resonators we measure loaded optical quality factors up to 11,000. Corresponding propagation loss of 5 dB/mm is also confirmed by measuring transmission through long waveguides.

We report on a general method to fabricate transition metal related defects in diamond. Controlled incorporation of Mo and W in synthetic CVD diamond was achieved by adding volatile metal precursors to the diamond chemical vapor deposition (CVD) growth process. Effects of deposition temperature, grain structure and precursor exposure on the incorporation efficiency were systematically studied, and doping levels of up to 0.25at.% have been achieved. The metal atoms are uniformly distributed throughout the diamond grains without any indication of inclusion formation. These results are discussed in context of the kinetically controlled growth process of CVD diamond.

Diamond has a unique combination of physical properties for the inertial confinement fusion ablator application, such as appropriate optical properties, high atomic density, high yield strength, and high thermal conductivity. Here, we present a feasible concept for fabrication of diamond ablator shells. The fabrication of diamond capsules is a multi-step process which involves diamond chemical vapor deposition on silicon mandrels followed by polishing, microfabrication of holes, and removing of the silicon mandrel by an etch process. We also discuss the pros and cons of coarse-grained optical quality and nanocrystalline chemical vapor deposition diamond films for the ablator application.

The infrared absorption of CVD diamond at a wavelength of 10.6 mu m was measured as a function of temperature between 20 and 500 degrees C. CVD diamond of different structural quality was investigated. Optical spectroscopy and infrared Raman scattering were used for the structural characterization. Laser calorimetry was applied to measure the IR absorption at elevated temperatures. For these measurements, CVD diamond devices with integrated heater and temperature sensor were prepared. The optical absorption at a given temperature was determined by comparing the temperature rise induced by CO2 laser irradiation with the equivalent electrically induced temperature rise.Samples with a room temperature absorption coefficient of alpha=0.096 cm(-1) and alpha=0.85 cm(-1) were investigated. Despite this large difference, the absolute increase of the absorption coefficient with increasing temperature was found to be similar for the two samples. It increased by a value of about 0.5 cm(-1) between 0 and 500 degrees C. (c) 2005 Elsevier B.V. All rights reserved.

A microprobe of protons with an energy of 17 million electron volts is used to quantitatively image three-dimensional hydrogen distributions at a lateral resolution better than 1 micrometer with high sensitivity. Hydrogen images of a <110>-textured undoped polycrystalline diamond film show that most of the hydrogen is located at grain boundaries. The average amount of hydrogen atoms along the grain boundaries is (8.1 ± 1.5) × 10 14 per square centimeter, corresponding to about a third of a monolayer. The hydrogen content within the grain is below the experimental sensitivity of 1.4 × 10 16 atoms per cubic centimeter (0.08 atomic parts per million). The data prove a low hydrogen content within chemical vapor deposition–grown diamond and the importance of hydrogen at grain boundaries, for example, with respect to electronic properties of polycrystalline diamond.

We report on measurements of resistivity and magnetoresistivity, Hall effect and upper critical field on normal and superconducting heavily boron-doped diamond layer produced by microwave plasma assisted chemical vapour deposition. The magnetoresistivity shows a characteristic change as a function of the boron concentration with strong evidence for a closed Fermi surface for superconducting samples. Although experimental and theoretical results favour a conventional, weak coupling electron–phonon interpretation of the superconducting mechanism, the observed dependence of the transition temperature TC on the hole concentration cannot be consistently described by the conventional theory.

The effect of nitrogen and boron doping on the thermal and optical properties of high purity CVD-diamond grown by microwave plasma (MW-CVD) and DC arc-jet chemical vapor deposition (DCAJ-CVD) is investigated. Boron and nitrogen doping was carried out by adding to the process gas trimethylborate and nitrogen, respectively. Secondary ion mass spectrometry (SIMS) was used to quantify the incorporated boron concentration. To decide whether or not nitrogen is substitutionally incorporated electron paramagnetic resonance (EPR) measurements were applied. The influence of the impurities on the thermal properties was investigated by measuring the temperature dependence of the thermal conductivity between 77 and approximately 450 K. Using the Klemens–Callaway-Theory, information about phonon scattering at point and extended defects was obtained. In the case of nitrogen addition to the MW-CVD process, no enhanced point defect scattering but instead an increase of scattering at extended defects or grain boundaries was observed. The nitrogen doped DCAJ-CVD sample showed the typical yellow color and EPR signal of diamond containing substitutional nitrogen. The point defect concentration determined by the Klemens–Callaway-Theory was six times higher as compared to the MW-CVD samples. CVD-diamond samples doped with 2.5×1019 cm−3 boron showed a bright blue color and absorption features indicating substitutionally incorporated boron. An enhanced phonon scattering due to point defects was not observed.

The RF device potential of surface-channel polycrystalline diamond metal-insulator-semiconductor field-effect transistors (MISFETs) is demonstrated for the first time, Utilizing a self-aligned gate field-effect transistor (FET) fabrication process, effective transconductance of 70 mS/mm is realized at 0.7 mum gate length. This FET also shows high f(T) and f(max) of 2.7 and 3.8 GHz, respectively. However, the breakdown voltage and f(max)/f(T) ratio are lower than those for the homoepitaxial layer because of the parasitic capacitance at the grain boundaries in the drain region. Because of the fluctuation of channel mobility, the fluctuation of g(m) and f(T) is observed. In order to realize high-power operation at high frequency, the fabrication of the FET on a single grain to reduce the parasitic capacitance is required.

The development and improvement of efficient microwave plasma reactors for diamond CVD is still an important topic and a prerequisite for the reliable production of high quality diamond films and wafers. We report on a novel reactor concept, the circumferential antenna plasma (CAP) reactor, which was developed on the basis of numerical FEM simulations. The electromagnetic field enters the plasma chamber through a ring-shaped circumferential window. The microwave power is guided to the window by radially expanding a coaxial waveguide. The design and simulation results of the CAP-reactor as well as a first prototype system powered by 6 kW microwave of 2.45 GHz will be described. The electric field distribution has been measured with a miniature microwave field probe and was found in perfect agreement with the FEM simulations. The CAP-reactor has been optimized to obtain a homogeneous flat plasma distribution above the substrate holder. Under these conditions CVD-diamond films and wafers have been deposited. Preliminary results will be presented.

The incorporation of hydrogen in thick polycrystalline chemical vapour deposition diamond plates has been studied by elastic recoil detection with a 2.8 MeV He+ microbeam. Hydrogen-rich inclusions of lateral dimensions 50–100 μm have been found and analysed quantitatively by depth resolved hydrogen area maps and line scans. The laterally averaged hydrogen content and its depth profile were also characterized by the 1H(15N, αγ)12C reaction. The observed hydrogen-rich inclusions correlate with features visible in optical microscopy but not with the optically visible crystallite topography.

Using ion channeling measurements in conjunction with the resonant 1H(15N,αγ)12C nuclear reaction or with proton Rutherford backscattering spectrometry we studied the incorporation of hydrogen from the plasma into homoepitaxial (100) and (111) CVD diamond films. The measured hydrogen concentration and the structural defect density of the diamond lattice derived from proton channeling yields were observed to be correlated. Hydrogen lattice location studies for different incident ion channeling directions showed no dominant fraction of H occupying either one of the two theoretically predicted sites. These results suggest that in CVD films with quite high dislocation densities and relative H concentrations above 10−3, hydrogen is predominantly incorporated at structural defect sites uncorrelated with the lattice symmetry.

The surface order of a heteroepitaxial diamond (001) film grown on an inclined β-SiC(001) has been evaluated with a micro-electron beam in ultra-high-vacuum. It was determined that the range of order of surface dimer-rows of the heteroepitaxial diamond film is ∼15 Å.

A computer program has been developed for the design and optimization of microwave plasma reactors used for the chemical vapour deposition (CVD) of diamond. The computer code consists of program modules for the calculation of electromagnetic field and plasma density distributions. The reliability of the simulation has been tested by modelling the reactor performance of the widely used cylindrical TM01 reactors, which show plasma instabilities at increased microwave power levels. An additional module is used for automatic optimization of the reactor performance. Based on the simulation program, a novel microwave plasma reactor employing an ellipsoidal cavity has been developed. This reactor has been realized and tested experimentally for microwave frequencies of 2.45 GHz and 915 MHz. The performance confirms the simulation results perfectly. Due to the plasma stability, these novel reactors are suitable for the growth of thick diamond layers with demonstrated areas up to 15 cm in diameter.

The effect of an inclined substrate on heteroepitaxial diamond has been investigated on 4° off β-SiC(001) tilted around the [1̄10] axis. Homogeneous macro steps with (001) terraces are observed in the [1̄10] direction forming a vicinal angle of 3°–4° from the (001) surface reflecting the substrate inclination. The selective growth is effective even if the dominant orientation is inclined by several degrees from the surface normal. The tilt deviation is less than 1° in the heteroepitaxial film. p-channel field effect transistors have been fabricated on these heteroepitaxial films. The device performance is as good as that on homoepitaxial films.

To investigate the in plane thermal diffusivity of chemical vapor deposited diamond layers, two new techniques were developed based on electrically induced converging and linear thermal waves. With these methods, free-standing, laser-cut diamond samples, 100 μm or larger in thickness can be analyzed. Laser cutting leaves a graphitic surface layer along the cutting edge. Therefore, a short high voltage pulse, applied at the graphitic rim resistor, is used to generate a thermal transient. The propagation of the wave is measured optically either in the center of the circular disk or at one side of a bar shaped sample. Both techniques require only very little sample preparation. They are shown to be simple, accurate, and independent of sample thickness and induced energy. In order to analyze the experimental data we present both an analytical model and a numerical simulation.

Numerical simulations were performed to predict the performance of microwave plasma reactors with various reactor geometries. The simulations include the calculation of the electric field distribution using the finite integration theory and the determination of the plasma density distribution based on a breakdown field algorithm. One reactor geometry with a cavity having the shape of a rotational ellipsoid turned out to be very promising. The electric field within this cavity exhibits two pronounced maxima at the two focal points of the ellipsoid. By coupling microwave energy into one maximum via an antenna, large electric field strengths can be generated in the counter maximum. This effect has been used to excite intense discharges that are very stable, spatially extended, homogeneous, and free from wall contact. These discharges were employed for the chemical vapor deposition of large area diamond wafers.

The low pressure deposition of polycrystalline diamond and the preparation of diamond windows at the Fraunhofer-IAF is reported. Using microwave plasma CVD, large area (2-6' diameter) diamond wafers with thicknesses of up to 2 mm have been grown. The deposition is carried out in a novel microwave plasma system which uses an ellipsoid cavity to generate very intense, spatially extended plasmas. Several of these plasma reactors with 6 to 60 kW microwave power are presnetly used at the IAF. The diamond wafers are ground and polished and laser- cut to the desired dimensions. To assess the optical and thermal properties, the residual absorption in the 10 micrometer range is determined by CO2 laser calorimetry, and temperature dependent and spatially resolved measurements of the thermal conductivity are performed. In addition, thermal expansion and refractive index measurements as a function of temperature are reported. Using high-purity process gases and optimized CVD conditions, diamond windows with a residual absorption at 10.6 micrometer below 0.1 cm-1 and a thermal conductivity over 20 W/cmK have been realized. In addition, low dielectric losses of tan(delta) equals 0.6 X 10-4 at 140 GHz have been measured.