C.-P. Klages

Epitaxial diamond thin films on (001) silicon substrates

Epitaxial (001) diamond film were grown on mirror‐polished single‐crystalline (001) silicon substrates by microwave plasma chemical vapor deposition from a methane/hydrogen gas mixture. The films were characterized by means of scanning electron microscopy, Raman spectroscopy, and x‐ray analysis. The results show that the diamond crystallites are oriented to the silicon substrate with both the (001) planes and the [110] directions parallel to the silicon substrate.

Heteroepitaxial diamond growth on (100) silicon

Abstract Highly oriented diamond films have been deposited on mirror-polished single-crystal (100) silicon by microwave plasma chemical vapour deposition. The crystallites are grown with their (001) planes parallel to silicon (001) and their [110] directions parallel to silicon [110], as shown by scanning electron microscopy and X-ray diffraction analysis.

Diamond film orientation by ion bombardment during deposition

The influence of ion bombardment during microwave plasma chemical vapor deposition (CVD) on diamond film orientation has been investigated. Two interesting findings were obtained: (1) The [001] axes of the grown diamond grains are always along the ion flow direction, perpendicular to the substrate and independent of the crystal orientation of the substrates and (2) for the crystallites which are homoepitaxially grown on the (001) diamond faces parallel to the substrate slight misorientations were found. These new findings confirm the role of ion impact in diamond CVD and can help us to understand the basic mechanism responsible for the crystal orientation in heteroepitaxial diamond films prepared using bias‐enhanced nucleation.

Atomic‐force‐microscopic study of heteroepitaxial diamond nucleation on (100) silicon

To understand the mechanism of heteroepitaxial diamond growth, the early stage of diamond nucleation, generated in a microwave plasma on negatively biased single crystalline (100) silicon substrates, was observed by atomic force microscopy. The results show that nonfacetted nuclei are initially formed whose size increases with deposition time. Reflection high energy electron diffraction reveals that the nuclei are of crystalline structure in spite of their very small height of about 5 nm. A critical radius of the nuclei rc seems to exist under conditions applied in this study. The initial nuclei have a preferential (100) orientation. By a proper control of the nucleation and growth process, however, one can allow the epitaxially generated nuclei to reach rc and to grow larger.

Coalescence and overgrowth of diamond grains for improved heteroepitaxy on silicon (001)

Heteroepitaxial [001]-oriented diamond films with considerably increased lateral grain size and strongly improved orientational perfection could be prepared by microwave plasma-assisted chemical vapor deposition using a [001]-textured growth process on Si (001) substrates followed by a [110] step-flow growth process. The diamond films were characterized by atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. The results indicate that the diamond crystals increase their lateral dimensions at the (001) film surface either by coalescence of grains combined with a termination of the propagation of grain boundaries or by changing the grain boundary plane orientations from preferentially vertical to preferentially parallel directions with respect to the (001) growth faces. In the second case, the grains with relatively large angle deviation from the ideal epitaxial orientation are overgrown by those with relatively small angle deviation. As a result, the degree of orienta...

Investigation of the high‐field conductivity and dielectric strength of nitrogen containing polycrystalline diamond films

The influence of nitrogen doping on the electrical properties of polycrystalline diamond films has been studied. The films were prepared in a microwave plasma chemical vapor deposition process using a H2/CH4/N2 gas mixture. The CH4 concentration was held constant at 0.5% and the nitrogen to carbon atomic ratio was varied between 0.01 and 0.2. The phase purities, surface morphologies, and the nitrogen contents of the films were analyzed by Raman spectroscopy, scanning electron microscopy, and secondary‐ion mass spectroscopy, respectively. From current‐voltage characteristics at field strengths up to 106 V cm−1 and in the temperature range between 300 and 800 K the conductivity was determined. The dielectric strength was obtained from the breakdown voltage measured using a voltage ramping rate between 50 and 100 V s−1. A minimum in high field and high‐temperature conductivity and a maximum in dielectric strength was found for the samples prepared with a nitrogen to carbon atomic ratio of 0.02. Compared with...

Deposition and characterization of diamond epitaxial thin films on silicon substrates

Heteroepitaxial diamond growth has been attempted on mirror-polished monocrystalline (001), (111), and (110) silicon substrates by microwave plasma CVD. The surface morphology and the crystallographic properties of the films were characterized by means of Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray diffraction, and X-ray and Raman pole-figure analysis. The results demonstrate epitaxial growth of diamond on both (001) and (111) oriented silicon substrates. Preliminary results give strong evidence for substrate-induced orientation of the diamond crystallites also on (110) oriented silicon substrate. The heteroepitaxy can be assigned to the oriented covalent bonding across the interface between diamond and silicon.

Approach of selective nucleation and epitaxy of diamond films on Si(100)

Heteroepitaxial diamond films were selectively nucleated and grown on mirror‐polished single crystalline (100) silicon by microwave plasma assisted chemical vapor deposition (MWCVD). The silicon substrates were coated by 0.5 μm thick SiO2 films patterned by a standard photolithography process. The selective nucleation was performed under a negative substrate bias condition. Results show that fine patterns of (100) oriented diamond films can be obtained with high deposition selectivity and fine‐line definition. In spite of the relatively large crystal size a structure edge roughness of <0.3 μm was achieved.

Photoconductivity of undoped, nitrogen- and boron-doped CVD- and synthetic diamond☆

Abstract Nitrogen-doped CVD- and synthetic type IIa and Ib diamonds were investigated by the constant photocurrent method (CPM). Nominally undoped CVD-films containing nitrogen show broad absorption bands with threshold energies at 1, 2.3, 3 and 4.2 eV. The typical nitrogen donor absorption band with a threshold at 1.7 eV is partially masked by the 1 eV band in CVD-films. The absorption bands are too broad to be described by simple theories based on photoionization of single unbroadened impurity levels. Boron-doped CVD- and type IIb synthetic diamond was studied by photoconductivity and photothermal ionization in the near infra-red. The large electron-phonon coupling in diamond gives rise to oscillatory photoconductivity minima due to fast capture of holes by the excited states of boron acceptors. In CVD-films with boron concentrations around 1019 cm−3, the oscillation pattern inverts at low temperatures and sharp minima were found in the spectrum.

Piezoresistivity of polycrystalline p-type diamond films of various doping levels at different temperatures

The piezoresistivity of polycrystalline p-type diamond films has been studied. The films were grown by microwave plasma assisted chemical vapor deposition and in situ doped with different concentrations of boron. A four-point electrical measurement was performed to evaluate the film resistivity change upon straining in a four-point bending beam setup. Films were glued directly onto a stainless steel beam and the silicon substrates were selectively removed. A gauge factor (relative change of the resistivity divided by the elastic strain) of about 690 under 100 microstrains was obtained at room temperature for a film doped with 32 ppm boron. With increasing temperature and dopant concentration the gauge factor increases. The experimental results obtained are discussed.