Single Crystal Boron-Doped Diamond Synthesis
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1203-J17-17
Single Crystal Boron-Doped Diamond Synthesis T. A. Grotjohn1, S. Nicley1, D. Tran1, D. K. Reinhard1, M. Becker2 and J. Asmussen1,2 1 2
Michigan State University, Electrical and Computer Eng., East Lansing, MI 48824, U.S.A. Fraunhofer USA Center for Coatings and Laser Applications, East Lansing, MI 48824, U.S.A.
ABSTRACT The electrical characteristics of high quality single crystal boron-doped diamond are studied. Samples are synthesized in a high power-density microwave plasma-assisted chemical vapor deposition (CVD) reactor at pressures of 130-160 Torr. The boron-doped diamond films are grown using diborane in the feedgas at concentrations of 1 to 50 ppm. The boron acceptor concentration is investigated using infrared absorption and a four point probe is used to study the conductivity. The temperature dependent conductivity is analyzed to determine the boron dopant activation energy. INTRODUCTION Diamond’s exceptional properties, such as a wide bandgap, high breakdown voltage, and high electron and hole mobilities, make it a potentially useful semiconductor for hightemperature and high-power devices. The realization of useful devices requires the deposition of high quality, controlled conductivity films. Our previous work [1,2] on the deposition of highquality boron-doped single crystal diamond measured the growth rates of boron-doped films as a function of the concentration of diborane and methane in the feedgas, with the aim of increasing the growth rate and the quality of the films. This earlier work demonstrated the deposition of thick boron doped layers up to 2 mm thick at rates up to 11.5 μm/hr. The deposition pressure used in this previous work was 135-160 Torr, which is higher than many other studies of boron doped diamond, as described in [1,2]. This work expands upon our previous effort by performing more electrical characterization of plasma-assisted CVD deposited diamond. EXPERIMENT Boron doped diamond was deposited on 3.5 mm x 3.5 mm HPHT diamond seeds using a microwave plasma-assisted CVD reactor [3]. The reactor operates at 2.45 GHz with a molybdenum substrate holder that is water cooled. The deposition conditions included pressures of 130-160 Torr, 1-50 ppm diborane concentration in the methane/hydrogen feedgas, 4-7.5% methane, and substrate temperatures of 800-1100 C. The seed substrates were acid cleaned and hydrogen plasma etched before deposition. Infrared Absorption The deposited diamond films were characterized using FTIR measurements to quantify the boron-related infrared (IR) absorption. IR absorption spectroscopy has proven to be a simple, nondestructive method of probing the electronic structure of semiconducting diamonds [4-7].
Collins and Williams [4] were the first to use the area under the absorption band at 347 meV (corresponding to transitions from the ground state to the excited states of the bound hole) to determine the concentration of boron in diamond. Using Hall Effect data taken on natural type IIb diamond, a calibration curve was developed. Interpretation of t
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