Effect Of Diamond Films Research Articles

Effect of diamond films as bufferlayer on formation of cubic boron nitride films by chemical vapor deposition

Boron nitride films are produced by the reaction of diborane (B 2H 6) and ammonia (NH 3) in a mixture of hydrogen and argon using microwave plasma-assisted chemical vapor deposition. Some parameters as NH 3/B 2H 6 ratios, hydrogen addition, substrate-bias voltage and working pressure are modulated to obtain high c-BN content in the film. The influence of diamond films with various grain sizes as bufferlayer on the formation of c-BN is investigated. As-grown BN/diamond films are characterized by Fourier transform infrared spectra, X-ray diffraction patterns and scanning electron microscopy. The results indicate that the nature of diamond film affects the amount of c-BN in the BN layer. Nanocrystalline diamond film can promote the c-BN formation, resulting in the c-BN content up to 85%. Thick c-BN/diamond multilayer up to 5.5 μm in total thickness and with nearly pure c-BN content is synthesized.

THEORETICAL STUDIES ON PIEZORESISTIVE EFFECT OF P-TYPE DIAMOND FILMS

In this paper, based on the Fuchs and Sondheimer theory and valence band split-off model, a theoretical description of the piezoresistive effect in P-type heteroepitaxial diamond films was presented by solving the Boltzmann transport equation in the relaxation time approximation, in which a mixed scattering by lattice vibration, ionized impurities and surface was considered. A calculating expression of the piezoresistive effect has been developed in a parallel connection resistance model for the light-hole band, the heavy-hole band and the split-off band. The calculating results were in good agreement with the experimental data, indicating that the prezoresistive effect in diamond films was mainly ascribed to the hole band split-off under a uniaxial stress.

Magnetoresistive effect in p-type semiconducting diamond films

Magnetoresistive effects were studied in p-type heteroepitaxial diamond films with a strip or Corbino disk structure in a magnetic field ranging from 0 to 5 T. The films were grown by microwave plasma chemical vapor deposition and boron doped by cold ion implantation and rapid thermal annealing. The experimental results show that the magnetoresistance (MGR) of p-type heteroepitaxial diamond films strongly depends on the geometric form of the samples and the magnetic field. Diamond films are assumed to be an isotropic isothermal solid in which conduction is by holes from light, heavy and split-off bands. Based on the Fuchs and Sondheimer thin-film theory, considering spherical energy surfaces and mixed scattering by lattice vibrations and ionized impurities and surface, a theoretical description of the magnetoresistive effect in diamond films is presented by solving the Boltzmann transport equation in the relaxation time approximation. A relationship between the MGR and the thickness of films, magnetic field, and mobility is shown.

The theoretical studies of piezoresistive effect in diamond films

Based on the Fuchs and Sondheimer thin film theory (F-S film theory) and a revised valence band split-off model, considering a mixed scattering by lattice vibrations, ionized impurities and surfaces, a theoretical description of the piezoresistive effect (PR effect) in p-type heteroepitaxial diamond films was presented by solving the Boltzmann transport equation in the relaxation time approximation and using the parallel connection resistance model. A calculating expression of the PR effect was given. The main characteristics that were identical with the experiment were obtained by theoretical calculation. Giving out a model to show that the energy level interval between the split-off band and the heavy-hole band was changed by strain, a reasonable explanation was presented for the error between experimental results and theoretical values of saturated PR effect under big strain.