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Published May 1, 2010 | Published
Journal Article Open

Phonon emission in germanium and silicon by electrons and holes in applied electric field at low temperature

Wang, G.

Abstract

The cryogenic dark matter search employs Ge and Si detectors to search for weakly interacting massive particle dark matter via its elastic-scattering interactions with nuclei while discriminating against interactions of background particles. These detectors distinguish nuclear recoils from electron recoils by simultaneously measuring phonon and ionization production in semiconducting substrates at sub-kelvin temperatures. They also reconstruct event position by quadrant-segmented measurement of the phonon signal. The ionization drift field does work on the electrons and holes. The charge carriers radiate this energy as acoustic phonons. At the typical applied field of 300 V/m in Ge (400 V/m in Si), we self-consistently model the behavior of the electrons and holes using independent drifted Maxwellian distributions, each characterized by an average drift velocity and an effective temperature, and including acoustic phonon emission. We calculate the phonon power angular and frequency distributions. We find that the bias polarity affects these distributions and, therefore, the phonon collection efficiency in Ge.

Additional Information

© 2010 American Institute of Physics. Received 16 September 2009; accepted 7 February 2010; published online 6 May 2010. The author thanks Blas Cabrera, Sunil Golwala, and Daniel Akerib for stimulating discussion and for support for this analysis. The work was done while author was at Case Western Reserve University, California Institute of Technology, and Argonne National Laboratory. The work was supported by the National Science Foundation under Grant Nos. AST-9978911 and PHY-9722414, by the Department of Energy under Contract Nos. DE-AC03-76SF00098, DE-FG03- 90ER40569, DE-FG03-91ER40618, and DE-FG02- 94ER40823, by FNAL, operated by the Universities Research Association, Inc., under Contract No. DE-AC02- 76CH03000 with the Department of Energy, and by the California Institute of Technology. The work at Argonne National Laboratory was supported by Office of Science and Office of Basic Energy Sciences of the U.S. Department of Energy, under Contract No. DE-AC02-06CH11357.

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