Studies On Magnetoresistive Effect In Diamond Films And Related Problems

In past several years, a significant magnetoresistive (MR) effect has been found in p-type diamond films. With the unique physical and chemical properties of diamond, it means that diamond films can be made as a new type of magneto-sensor material, which can greatly extend their applications in electronic industry.The diamond films were fabricated by microwave plasma CVD and the boron-doped was created by the cold ion implantation. The diamond films were characterized by SEM and Raman spectroscopy. With the four-probe method, the magnetoresistance measure-ments have been carried out in a magnetic field ranging from 0 to 5T. It was found that the MR effects of diamond films strongly depended on the magnetic,the geometry of sample and temperature. The changes in the resistance are 0.40 for the strip sample and 0.85 for disk sample under magnetic field of 5T respectively. Under a certain magnetic field, the MR of strip sample has a significant form effect, and is proportional to the width-to-length ratio of the strip sample. Moreover, the MR is sensitively to the temperature. When temperature increased from 300K to 500K and the magnetic field was 5T, the MR of disk was decreased from 0.85 to 0.15. But up to date, the origin of the significant MR effect and the abundant properties of diamond films is still unknown. The MR effects of diamond films and the related problems have been studied systemically in this dissertation. Based on the Fuchs- Sondheimer thin film theory ( F-S theory ), a mixed scattering by lattice vibrations,ionized impurities and surfaces was considered. Taking the parallel connection resistance model, a theoretical description of the MR effect in heteroepitaxial diamond films is presented by solving the Boltzmann transport equation in the relaxation time approximation. The calculation equation of MR effect has been obtained. The theoretical calculation is consistent with experimental result.The influences of Hall effect on MR effect of diamond films have been investigated. It shows that the form effect of strip sample is caused by the changes of the Hall electric field with the width-to-length ratio of the strip sample.According to the valence bands split model and F-S thin film theory, a calculation formula of piezoresistive effect has been presented. A theoretical calculation was made to the piezoresistive effect of the diamond films. A united analytical expression for the piezoresistive and magnetoresistive effect has firstly been developed. The influences of magnetic field on the piezoresistive effect and the influences of stress on the magnetoresistive effects were theoretically analyzed.The valence bands split-off caused by internal stress was pretended, in which the valence bands split-off change with temperature. The MR and PR in diamond films have been researched when temperature changes. It has been found that the MR and PR could be influenced greatly by the change of valence bands split-off with temperature.In addition, some problems to be researched are suggested and the applications of the MR effect of diamond films are prospected...