Hot Carrier Velocities in Doped and in Ultra-pure Germanium Crystals at Millikelvin Temperatures

Olivieri, E.; Broniatowski, A.

doi:10.1007/s10909-012-0535-5

Cited by 3 publications

(3 citation statements)

References 9 publications

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“…For an order of magnitude estimate, we consider the case of holes, whose drift velocity at mK temperatures under an electric field of 0.5 V/cm is about 2x10 6 cm/s. 1 (Similar values obtain for electrons.) Assuming a magnetic field of 5 gauss (∼ ten times the terrestrial field) at right angle to the electric field, the ratio of the magnetic to the electric force is ~ 0.2, (*) corresponding author.…”

Section: Introductionsupporting

confidence: 62%

Effects of a Weak Magnetic Field on Carrier Transport in a Cryogenic Germanium Detector for Dark Matter Search

2012

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A magnetic field of a few gauss produces sizeable effects on carrier transport and charge collection in a germanium dark matter detector operated at millikelvin temperatures. The magnitude of the effects is explained by the large values of the velocities imparted to the carriers, even under the low electric field conditions typical for charge collection in these devices (a few 10 6 cm/s at ~ 1 V/cm). Using a suitable experimental setup, effects of the magnetic field on electron and hole transport were investigated separately. A dependence of these effects on the orientation of the field relative to the detector axis is demonstrated, arising in part from magnetic flux conservation through the superconducting (Al) annular electrodes on these devices.

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Section: Introductionsupporting

confidence: 62%

Effects of a Weak Magnetic Field on Carrier Transport in a Cryogenic Germanium Detector for Dark Matter Search

2012

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“…This model will be valid on the condition that phonon scattering be isotropic, and that the intervalley scattering time be long compared to the intravalley scattering time, so that the energy distribution of the electrons in each valley is determined only by intravalley scattering. 2 A closed expression then obtains for the drift velocity v i of an electron in the ith valley as a function of the field E. A single set of experimental data is needed in order to determine this dependence explicitly, namely the electron velocity-versus-field relationship along the <100> symmetry axis [10,11]. 1 The mean value of the field in this distribution is ∼10(q/4πε 0 ε r )N 2/3 scatt , which gives 1 V/cm for N scatt ∼ 4 × 10 10 cm −3 .…”

Section: Impurity Scattering and Electron Anisotropymentioning

confidence: 99%

“…As an approximation, we neglect the hole anisotropy altogether, and apply to all field orientations the same velocity-versus-field relationship, as determined in the <100> direction of the field [11].…”

Section: Impurity Scattering and Electron Anisotropymentioning

confidence: 99%

Carrier Anisotropy and Impurity Scattering in Ge at mK Temperatures: Modeling and Comparison to Experiment

Broniatowski

2012

J Low Temp Phys

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Improving upon the present background rejection capabilities of the cryogenic germanium detectors for direct dark matter search involves an in-depth comprehension of the charge collection process in these devices. Experimental data point to the combined effects of lattice and impurity scattering on the anisotropy of electron transport in Ge at mK temperatures. A Monte Carlo simulation code has been implemented to incorporate these features in a consistent model for charge collection. In a novel approach to carrier scattering by charged impurities in Ge at cryogenic temperatures, the scattering field of the impurities is treated statistically as a random contribution to the collection field, described by the Holtsmark distribution function with a single adjustable parameter, the mean density of the charged centers. Simulation of charge collection along these lines in devices different by their impurity content shows excellent agreement to experiment. Especially noteworthy is the fact that the strength of impurity scattering is reversed from the known concentration of dopant impurities in the crystals, as the crystal with the higher dopant concentration shows lower scattering at low field than the one with the lower concentration. This raises as an issue for further improvement of these devices, the question of the nature of the scattering centers in high-purity Ge crystals at cryogenic temperatures, associated presumably with deep level impurities or crystal defects. Fig. 1 (Color online) (a) Simulated carrier trajectories for a 60 keV energy deposit from a collimated 241 Am γ source facing the bottom surface of the detector crystal. See Ref. [1] for a full description of the device and of the geometry of the charge collection field especially. Detector bias V p = 2 V; T = 20 mK. Holes are in red and electrons in blue, black, green and magenta depending on their valley of belonging. (b) Same as (a), with the polarity of the electrode biases reversed so that holes instead of electrons are drifted across the full thickness of the detector crystal

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Hot Carrier Trapping in High-Purity and Doped Germanium Crystals at Millikelvin Temperatures

et al. 2014

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A new set of experimental data is presented for the mean drift lengths and the drift velocities of hot electrons and holes as a function of the electric field in ultra-pure and in lightly doped (n- and p-type) germanium single crystals at mK temperatures. Measurements are made in the field range between 0.1 and 15 V/cm, typical for the operation of cryogenic germanium detectors for dark matter search. The analysis of the experimental data strongly suggests that the dominant trapping centers are the dopant species in the neutral state

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Hot Carrier Velocities in Doped and in Ultra-pure Germanium Crystals at Millikelvin Temperatures

Cited by 3 publications

References 9 publications

Effects of a Weak Magnetic Field on Carrier Transport in a Cryogenic Germanium Detector for Dark Matter Search

Effects of a Weak Magnetic Field on Carrier Transport in a Cryogenic Germanium Detector for Dark Matter Search

Carrier Anisotropy and Impurity Scattering in Ge at mK Temperatures: Modeling and Comparison to Experiment

Hot Carrier Trapping in High-Purity and Doped Germanium Crystals at Millikelvin Temperatures

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