Münster 1999 – scientific programme
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HL: Halbleiterphysik
HL 23: Poster II
HL 23.17: Poster
Wednesday, March 24, 1999, 14:00–18:00, Z
Transport parameters of n-GaAs before and after the low-temperature impurity breakdown — •V. Novák1, J. Hirschinger2, D. Schowalter2, W. Prettl2, and F.-J. Niedernostheide2 — 1Ústav pro elektrotechniku AVČR, Dolejškova 5, 182 02 Praha, Czech Republic — 2Institut für Angewandte und Experimentelle Physik, Universität Regensburg, 930 40 Regensburg
At helium temperatures n-GaAs is known to exhibit an electric breakdown if the applied electric field exceeds a critical threshold value. During the breakdown the conductivity increases by several orders of magnitude due to the increase both in electron density and in electron mobility. In order to measure the transport parameters the influence of the inhomogeneous current has to be eliminated. This has been done using the standard Hall technique combined with the luminescence imaging of the filamentary current flow and numeric simulation of the current density distribution in the real sample geometry. The increase in the electron mobility during the breakdown has been found to be more than one order of magnitude, which agrees well with the direct Hall angle measurement based on filament tilting in magnetic field. This result can explain the observed bistability of the sample conductivity in terms of substantially enhanced electron energy, which sustains the impact ionization of shallow impurities even in sub-threshold electric fields.