Galina Popovici

Wide band gap electronic materials

Preface. Diamond:- Growth and Doping. Characterization and Properties. Applications. Amorphous and Diamond-Like Carbon Films:- Growth and Doping. Characterization and Properties. Applications. Other Wide Band Gap Semiconductors:- Growth and Doping. Characterization and Properties. Applications. Oral Presentations. Poster Presentations. Author Index. Key Word Index.

Prospective n-type impurities and methods of diamond doping

Abstract A major goal of diamond thin film technology research has been the reproducible production of p-n junctions, which are the basic units of many electronic devices. While p-type conductivity is relatively easily attained by boron doping, n-type conductivity has proved much harder to achieve. The experimental and theoretical results on prospective donor impurities are reviewed. In analogy with classical semiconductors, we will discuss the possibility of obtaining n-type diamond by using substitutional impurity atoms (nitrogen and phosphorus) and interstitial atoms (Li and Na). New methods of forced diffusion and ion assisted doping during growth are discussed. Methods of forced introduction of impurities into the diamond lattice have an important advantage over traditional ion implantation methods. Ion implantation introduces structural defects (vacancies, vacancy + interstitial, and their combinations) that are difficult to cure. Both methods, forced diffusion and ion assisted doping during growth, introduce no additional structural defects, except that inherent to the impurity itself.

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 .

Silver on diamond Schottky diodes formed on boron doped hot‐filament chemical vapor deposited polycrystalline diamond films

Schottky diodes were fabricated using sputter deposited silver contacts to boron doped polycrystalline diamond thin films grown by a hot‐filament chemical vapor deposition process with trimethyl borate as an in situ dopant source. High forward current density and a high forward‐to‐reverse current ratio were exhibited by these diodes. Current density‐voltage and capacitance‐voltage‐frequency characteristics of these diodes are very similar to those of Schottky diodes fabricated using a single‐crystal diamond substrate.

Effect of mechanical stress on current-voltage characteristics of thin film polycrystalline diamond Schottky diodes

Schottky diodes utilized for mechanical stress effect studies were fabricated using aluminum contacts to polycrystalline diamond thin films grown by a hot‐filament‐assisted chemical vapor deposition process. Compressive stress was found to have a large effect on the forward biased current‐voltage characteristics of the diode, whereas the effect on the reverse biased characteristics was relatively small. This stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects that dominated the diode current‐voltage characteristics in the small and large bias regions, respectively. At a large constant forward bias current, a good linear relationship between output voltage and applied force was observed for force of less than 10 N, as predicted by the piezoresistance effect. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. Compared to either silicon or germanium junction diodes and tunnel diodes, polycrystalline diam...

Growth of oriented aluminium nitride films on silicon by chemical vapour deposition

Aluminium nitride films were grown on silicon substrates using the chemical vapour deposition (CVD) method. The properties of the films were studied by scanning electron microscopy (SEM), atomic force microscope (AFM) measurements, X-ray diffraction and Raman scattering. The resulting films were strongly textured and had a preferential orientation with the c-axis normal to the surface, the Raman spectra showed two peaks at 607 and 653 cm−1 and two large bands at 750 and 900 cm−1 of smaller intensity. Both the macro- and micro-Raman spectra showed the same peaks.

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.

Boron diffusion into diamond under electric bias

Three natural type IIa diamond crystals were used for forced diffusion of boron. The diffusion was performed under bias otherwise with the same conditions. The boron diffusion coefficient in diamond was found to be 8.4 × 10 −15 and 4 × 10 −14 cm 2 /s at 1000 °C, depending on the direction of the electric field. The drift velocity of boron in diamond under 850 V at 1000 °C was found to be about 1.2 × 10 −8 cm/s.

Smooth diamond films grown by hot filament chemical vapor deposition on positively biased silicon substrates

Abstract Smooth diamond films have been grown by hot filament chemical vapor deposition under DC bias on mirror-polished Si(100) substrates. Films of a few micrometers thickness were obtained in 30 min. The films were found to have d -spacing at 2.06 and 2.11Aby X-ray diffraction. Raman spectra showed very broad peaks at 1329 (1336) and 1591 cm -1 . The films have a high density of planar defects and large internal stresses.