Abstract
The purpose of this experiment is to observe the oblique propagation of electrons through germanium by exciting a point source of charge carriers with a focused laser pulse on one face of a germanium crystal. After the electrons are drifted through the crystal by a uniform electric field, the pattern of charge density arriving on the opposite face is mapped and used to reconstruct the trajectories of the electrons. These measurements will verify in detail the Monte Carlo analysis utilized in the Cryogenic Dark Matter Search to model the transport of charge carriers in high-purity germanium detectors, including both oblique electron propagation and inter-valley scattering.
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Notes
The impurity concentration was \(8\times 10^9\) per cm\(^{3}\).
400 Å amorphous-Si, 200 Å Al, and 400 Å W.
2 \(\upmu \)m wide lines, with a 10 \(\upmu \)m pitch.
This repetition rate was chosen to place the 10 kHz noise spike (see Fig. 5) between the 10th and 11th harmonics of the fundamental frequency.
This relatively high energy per pulse was chosen to give clearly measurable signals. The energy per pulse will be reduced in future measurements.
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Acknowledgments
This work was supported in part by the U.S. Department of Energy and by the National Science Foundation. Robert Moffatt is also thankful for financial support from The Robert and Marvel Kirby Stanford Graduate Fellowship. The authors are also especially grateful to the staff of the Varian Machine Shop at Stanford University for their assistance in machining the parts used in this experiment, and to members of Mirrorcle Technologies Inc., who provided a great deal of time and assistance in implementing the MEMS system.
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Moffatt, R.A., Cabrera, B., Kadribasic, F. et al. Spatial Imaging of Charge Transport in Germanium at Low Temperature. J Low Temp Phys 176, 943–951 (2014). https://doi.org/10.1007/s10909-013-1013-4
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DOI: https://doi.org/10.1007/s10909-013-1013-4