Electrical Properties of Natural IIa Diamonds Using Photo- and Particle Excitation
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ELECTRICAL PROPERTIES OF NATURAL IIA DIAMONDS USING PHOTO- AND PARTICLE EXCITATION L. S. PAN*, S. HAN*, D. R. KANIA*, K. K. GAN**, S. ZHAO**, H. KAGAN**, R. KASS**, R. MALCHOW**, F. MORROW**, W. F. PALMER**, C. WHITE**, S. K. KIM***, F. SANNES***, S. SCHNETZER***, R. STONE***, G. B. THOMSON***, Y. SUGIMOTOt, A. FRytt, S. KANDA, S. OLSENttt, M. FRANKLIN3, J. W. AGER III44, AND P. PIANETrAfl 4 * L-476, Lawrence Livermore National Laboratory, Livermore, CA 94550 ** Department of Physics, The Ohio State University, Columbus, OH 43210 *** Department of Physics and Astronomy, Rutgers University, Piscataway,
NJ 08854 t KEK Laboratory, Tsukuba-shi, Ibaraki-ken, Japan 305 tt Physics Division, SSC Laboratory, Dallas, TX 75237 tt$ Department of Physics, University of Rochester, Rochester, NY 14627 3 Department of Physics, Harvard University, Boston, MA 02138 44 Center for Advanced Materials, Lawrence Berkeley Laboratory, Berkeley, CA 94720 #*4 Stanford Synchrotron Radiation Laboratory, SLAC, Stanford, CA 94309
ABSTRACT
Two complementary techniques are used to study the electrical transport properties related to the use of diamonds as materials for ionizing radiation detectors. Transient photoconductivity using soft x-rays is used to probe the first few microns of the material, while ionizing particle-excited conductivity is used to probe the entire bulk of the material (1 millimeter). Both techniques measure the mean drift distance of free carriers, or the collection distance d. In addition, transient photoconductivity is able to extract the lifetimes and mobilities of the excited carriers. The collection distance measured by the two methods are in agreement, suggesting the material is homogeneous. At an applied field of 10 kV/cm, d is 25 to 30 microns, and, up to a field of 25 kV/cm, d has not saturated. The lifetime varies between 100 and 600 ps, and the mobility varies between 1000 and 4000 cm 2/V-s, the range due to natural variations from sample to sample. The primary defects limiting the lifetime are believed to be nitrogen impurities and dislocations. INTRODUCTION AND EXPERIMENTAL SETUP Single-crystal natural Ha diamonds have been used for years as detector material for ionizing radiation. Among the attractive properties of diamond are its high electron and hole mobilities, high dielectric breakdown strength, and high resistance to radiation damage. With the development of synthetic diamonds deposited by chemical vapor deposition, the properties of diamond can potentially be controlled and large areas may become available. However, to date, these synthetic films are generally polycrystalline. Thus, to understand the transport properties without the complication of grain boundaries, the study of single-crystal natural samples is fundamental. In this paper, we discuss two techniques used to measure transport properties associated with the use of diamond for radiation detection. The dark resistivity of diamond is extremely high, due to its low intrinsic carrier concentration. In order to measure electrical transport, f
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