S. Khasawinah

DIFFUSION OF BORON, LITHIUM, OXYGEN, HYDROGEN, AND NITROGEN IN TYPE IIA NATURAL DIAMOND

Diffusion of boron, lithium, nitrogen, oxygen, and hydrogen into type IIa natural diamond was studied. The diffusion was performed in two steps. First, diffusion of Li and oxygen was performed in nitrogen atmosphere at 860 °C for one hour. The sample was then placed in a hot filament chemical vapor deposition (CVD) growth reactor and diffusion was performed for two hours in hydrogen atmosphere from a boron solid source placed on the surface of the sample. The condition of diffusion were those used routinely during CVD growth. After diffusion, the concentration of Li was of the order of 2×1016 cm−3 at the depth of 0.5 micrometer, and oxygen, nitrogen, and boron were found to be in the range (1–4)×1020 cm−3 at the same depth. The diffusion of hydrogen under conditions specific to CVD growth has also been studied for the first time and was found to be quite strong.

FORCED DIFFUSION OF IMPURITIES IN NATURAL DIAMOND AND POLYCRYSTALLINE DIAMOND FILMS

A method is proposed for the determination of the state of an impurity (donor, acceptor, or deep level) in semiconductor lattice. To demonstrate the method boron was diffused into type Ia natural diamond under a dc electric field. The concentration and diffusion profiles of boron were affected by the applied field. Boron diffuses as a negative ion since it is an acceptor shallow enough to be partially ionized at the temperature of diffusion. The drift velocity of boron ions at the temperature of diffusion was also estimated. The diffusion of lithium and oxygen from a Li2CO3 source in chemical vapor deposited diamond films was performed under bias at 1000 °C in an argon atmosphere. After diffusion, the concentrations of Li, O, and H in the diamond films were found to be around (3–4)×1019 cm−3. No dependence of these concentrations on the applied bias was observed. It was found that the diffusion of Li goes primarily through grain boundaries, which may explain why it does not depend on the applied voltage. ...

Properties of diffused diamond films with n-type conductivity

Abstract High quality, freestanding “white” CVD diamond films, 230 μm thick, polished on both sides and with resistivity 10 14 Ω cm were used for diffusion of impurities to obtain n-type conductivity. Diffusion of lithium, oxygen and chlorine was performed under a bias. Auger analysis was used to determine the impurity concentrations. After diffusion, the concentrations of Li, O and Cl in the diamond films were found to be about (3–4) × 10 19 cm −3 . Raman scattering, cathodoluminescence, microwave photoconductivity, electron spin resonance, optical absorption, Hall effect and electrical conductivity measurements were employed for the film characterization. The measurements showed that the initial high structural quality of the film was not deteriorated after diffusion. The hall effect measurements showed n-type conductivity. The sheet resistance of the diffused layer was 10 5 Ω/□. The carrier mobility was estimated to be about 50 cm 2 V −1 s −1 .

Study of color centers in hot-filament CVD diamond films by cathodoluminescence and photoluminescence and their correlations with film quality

Abstract The color centers on the front and back of five free-standing diamond films grown by hot-filament CVD were characterized by cathodoluminescence and photoluminescence. The film quality was assessed by measuring the full width at half-maximum (FWHM) of the characteristic Raman diamond peak at 1332 cm−1. A correlation between the color center luminescence and the film quality was derived. The cathodoluminescence study clearly showed that the intensities of band A and the 600 nm emission band increased with increasing quality. Conversely, the intensity of the 1.68 eV photoluminescence decreased as the film quality improved. The lower intensity of the 1.68 eV luminescence in higher quality films, observed in the samples grown in a silicon-free reactor, is different from the usual 1.681 eV luminescence from silicon-related centers, which shows a greater intensity in higher quality films.

Neutron irradiation and annealing of 10 B doped chemical vapor deposited diamond films

10B doped diamond films grown by hot filament chemical vapor deposition were neutron irradiated at moderately high fluence levels. The as-irradiated and annealed samples. along with an unirradiated sample, were analyzed using Raman spectroscopy and x-ray diffraction. It was found that a non-diamond amorphous phase was formed on irradiation. This phase transformed back to diamond on annealing. No graphite formation was observed. A comparison with nanodiamond powder was made. A similarity between irradiated diamond films and nanocrystalline diamond powder is discussed.

Properties of Li doped diamond films, obtained by transmutation of 10B into 7Li

Abstract 10 B doped diamond films grown by hot filament chemical vapor deposition were neutron irradiated for 4 weeks. The as-irradiated, and annealed samples, along with unirradiated samples, were analyzed using Raman, cathodoluminescence, and electrical conductivity measurements. The feasibility of the restoration of the quality of the irradiated films upon annealing was shown. The cathodoluminescence and electrical resistivity measurements showed that donor centers are formed during annealing in the irradiated samples. These donor levels may be Li atoms that move into interstitial sites of the lattice and become donors. The other possibility is the formation of donor levels owing to the interaction of Li atoms with some lattice defects induced by neuron irradiation. Prime novelty: transmutation doping of diamond using reaction 10 B (n, α) 7 Li.

Wide Band-Gap Photovoltaics

Wide bandgap materials will have many applications as coatings and as electronic devices. This paper describes an electronic application for wide bandgap materials in energy production. A specific portable power technology which converts the energy emitted from nuclear reactions to electrical energy using wide bandgap photovoltaic cells without intermediate thermalization is described in this paper. The potential efficiency for the photovoltaic process is 35%, nuclear energy to electrical energy. And, if combined with high-temperature thermionic conversion the nuclear to electrical energy conversion efficiency is 41% while the overall size of the system remains small. The key to the process is to first convert the high-grade ion energy to photon energy, which can then be directly converted to electrical energy. This process is also usable as an advanced topping cycle for large scale energy production in conjunction with fusion power, as well as fission power. In addition to improved efficiency, the process also promises advantages in smaller volumes, smaller mass, and lower cost of the energy conversion hardware.

Thermal desorption study of bonded hydrogen in diamond films

Abstract The amount of bonded hydrogen in polycrystalline diamond films grown by hot filament CVD at various deposition temperatures was measured by the thermal desorption method. The amount of hydrogen evolved from as-grown diamond films had the tendency to increase with deposition temperature. After vacuum annealing at 1470 K the samples were exposed to air at room temperature. It was shown that the presence of bonded hydrogen in these films was related to water adsorption on the diamond surface. The surface morphology of the films was studied by scanning electron microscopy. It was found that the higher the deposition temperature and the greater the sample thickness, the larger are the crystals with {111} faces.

Diffusion of Impurities Under Bias in CVD Diamond Films

The diffusion of oxygen, lithium, chlorine, and fluorine in CVD diamond films was performed under bias at 700 and 1000 °C. SIMS and Auger analyses were used to determine the impurity concentration. After diffusion, the concentrations of Li and O in the diamond films were found to be of the order of (3–4)×10 19 cm -3 . The fluorine concentration was of order of (l-2)×10 17 cm -3 . The conductivity was p-type. The change in the resistivity due to diffusion was nearly nine orders of magnitude for the sample diffused under electric field, and six orders of magnitude for the samples diffused without field. No dependence of the impurity concentration on the applied bias was observed except for fluorine. The fluorine concentration dependence on the electric field indicates that fluorine may have formed a shallow level in the diamond band gap. The fact that large concentrations of impurities can be diffused into diamond films at relatively low temperatures indicates the presence in the films of many lattice defects (including grain boundaries).

Raman and FTIR Study of Neutron Irradiated CVD Diamond

Undoped and 10 B doped diamond films were neutron irradiated at a moderately high fluence level (thermal neutron fluence of 1.3 × 10 20 n/cm 2 and a fast neutron (E> 0.1 MeV) fluence of 1.6 × 10 20 n/cm 2 ). The unirradiated, irradiated, irradiated and annealed samples were studied using Fourier Transform Infrared (FTIR) and Raman spectroscopies. A dependence of radiation induced stress on the initial boron concentration was observed. The radiation induced stress was lower for the undoped samples. Correlations between FTIR and Raman data were found. The radiation damage was removed after annealing, as measured by Raman and FTIR spectroscopy.