Abstract
The microwave induced breakdown characteristic inn-type germanium at 4.2 °K has been observed and compared with the d.c. induced breakdown characteristic obtained from the same sample. The effective microwave breakdown field intensity is nearly equal to the field intensity observed in d.c. induced breakdown. However, in the breakdown region with conductivities greater than 0.1 ohm−1 cm−1 a relaxation effect was found and interpreted qualitatively as momentun relaxation. In the initial breakdown the relaxation time τ m is small,ω 2τ 2 m being ≪1 whereω/2π=9·109s−1 is the microwave frequency. The relaxation time is determined by predominant neutral impurity scattering with at last 5·1014 impurities per cm3. This scattering mechanism becomes ineffective when the impurities are ionized by hot carriers. Ionized impurity scattering or acoustic phonon scattering will then be predominant with increased and energy dependent values of τ m . The increased phase shift between carriers and field causes a decreased energy transfer from the field to the carriers, an accordingly smaller ionization rate, and finally results in a nearly constant a.c. conductivity.
The observed anisotropy of the breakdown field intensity is in qualitative agreement with the assumption that only carriers in “hot” valleys of the conduction band initiate the breakdown by impact ionization. The unsufficient quantitative agreement may be due to an inhomogeneity of doping which is suggested by comparing the values of the ohmic low temperature conductivity of the samples.
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Die Arbeit wurde auf Einladung von Herrn Professor G.Lautz am Institut für Kernphysik/Abteilung Festkörperphysik der Universität Kiel durchgeführt. Herrn ProfessorLautz und seinen Mitarbeitern danke ich sehr herzlich für ihre Unterstützung bei der Durchführung der Arbeit. Insbesondere gebührt Herrn Dipl.-Phys. E.Fay Dank für die sehr erfreuliche Mitarbeit bei den Tieftemperatur-Experimenten und die leihweise Überlassung seines Kryostaten. Herrn ProfessorLautz und Herrn Professor H. G.Reik danke ich für zahlreiche Diskussionen, Herrn Professor O.Haxel danke ich für sein reges Interesse und die stete Förderung der Arbeit. Die Deutsche Forschungsgemeinschaft hat die Arbeit durch Leihgaben dankenswerterweise unterstützt.
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Seeger, K. Reversibler Gleichfeld- und Mikrowellen-Durchschlag in n-Typ-Germanium bei 4,2 °K. Z. Physik 182, 510–520 (1965). https://doi.org/10.1007/BF01380882
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DOI: https://doi.org/10.1007/BF01380882