Synthesis and Characterization of Boron-Doped Single Crystal Diamond
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Synthesis and Characterization of Boron-Doped Single Crystal Diamond Sunil K. Karna1, D. V. Martyshkin1, Yogesh K. Vohra1 and Samuel T. Weir2 1 Department of Physics, University of Alabama at Birmingham, Birmingham, AL 35294, USA 2 L-041, Lawrence Livermore National Lab., Livermore, CA 94550, USA ABSTRACT The boron-doped single crystal diamond films were grown homoepitaxially on synthetic (100) oriented Type Ib diamond substrates using a Microwave Plasma Chemical Vapor Deposition (MPCVD) technique. Raman spectrum showed a few additional bands at the lower wavenumber regions along with the zone center optical phonon mode for diamond. The change in the peak profile of the zone center optical phonon mode and its downshift were observed with the increasing boron content in the film. A modification in surface morphology of the film with increasing boron content had been observed by atomic force microscopy. Four point probe electrical measurement indicated that different conduction mechanisms are operating in various temperature regions for these semiconducting films. INTRODUCTION Diamond is an excellent research material for its outstanding inherent properties. It can change the functionality and lifespan of many future electronic devices by proper level of impurity doping. There have been reports on various levels of doping during the diamond growth process using the microwave plasma assisted chemical vapor deposition (MPCVD).1-5 However, the growth of device grade diamond is an area of continued research interest. Hence, our study was based on the optimization of growth conditions of semiconducting high quality boron-doped single crystal diamond using MPCVD. In order to understand the effect of boron in the diamond lattice, Raman spectroscopy and electrical conductivity of the films were analyzed in detail. EXPERIMENT Boron doped single crystal diamond films were synthesized homoepitaxially on (100) oriented Type Ib diamond substrates. The diamond seeds of dimensions 3.5×3.5×1.5 mm3 were used as substrates in a 2.45 GHz bell jar MPCVD system. The deposition time was set for 8 hours. The reactant gas B2H6 with 6 to 8% of CH4 in H2 mixture was used for the deposition. The (B/C)gas ratio for film BD1 was kept at 2300 ppm and that for films BD2 and BD3 was maintained at 6200 ppm. The details of deposition parameters and growth rate of samples (BD1, BD2, and BD3) are summarized in Table 1. The diamond film grown without boron doping is referred to as HD in Table 1. To avoid hydrogenation effect in CVD diamond, electrical measurement was taken during cool down procedure in a four point probe vacuum chamber. Raman spectra were recorded using a 514.5 nm laser excitation wavelength at room temperature. X-ray rocking curve measurements were taken by rotating sample with 0.02o angular step with detector set at a fixed 2theta value corresponding to (400) Bragg diffraction peak from the diamond crystal. Non-contact mode atomic force microscopy (AFM) was used to measure surface morphology of films in this study. Doping level and ele
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