## Abstract

First investigations are reported on the temperature dependence of the dc‐conductivity at T = = 0.05 to 300 K on neutron‐transmutation‐doped (NTD) n‐GaAs in the vicinity of the metalinsulator transition (MIT). At a medium compensation of K = 0.60 to 0.77 the MIT takes place at the critical electron concentration of n_{c} = 2.3 × 10^{16} cm^{−3}. On the dielectric side of the MIT in the variable‐range hopping regime (VRH) at T ≦ 10 K the conductivity obeys the equation σ(T) = σ_{0}exp [— (T_{1}/T)^{1/2}] and not the Mottlaw. The experimental values T_{1} are for all samples much smaller than T_{1}^{theor} for isolated shallow impurities and scale down according to T_{1} = = T_{1}*(1 ‐ n/n_{c})^{1.6±0.4} with T_{1}* = 5.9 K by approaching the MIT. This behaviour is due to the divergency of the localization radius a and the static DK ϵ_{0} at the MIT. The obtained linear In σ — T^{−1/2} law over about 2.5 orders of magnitude in temperature variation and more than three orders of magnitude of variation in conductivity is interpreted in the frame of a Coulomb gap with vanishing density of states at the Fermi level, as predicted by Efros and Shklovskii. The pre‐exponential factor ϱ_{0} = σ_{0}^{−1} shows also scaling behaviour according to ϱ_{0} = ϱ_{0}*(1 ‐ n/n_{c})^{1.2±0.4} and a value of ϱ_{0}* = 2.2 Ω cm. At n → n_{c} σ_{0} = ϱ_{0}^{−1} reaches the value of Mott's minimal metallic conductivity of σMM = (Ce^{2}/h) n_{c}^{1/3}, with 0.025 ≦ C ≦ 0.05.

Original language | English |
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Pages (from-to) | 691-700 |

Number of pages | 10 |

Journal | Physica Status Solidi (B): Basic Research |

Volume | 137 |

Issue number | 2 |

DOIs | |

State | Published - 1 Oct 1986 |

Externally published | Yes |