Temperature (T) dependence of conductivity (σ) was studied in semi-insulating GaAs as a function of the magnetic field (B) for 1.8 K < T < 40 K for high electric fields. An infrared illumination of a sample and application of an electric field caused a non-equilibrium distribution of electrons in the conduction band. An increase in B caused a localization transition which manifested itself by a gradual disappearance of the impact ionization of shallow bound states. The transition was connected with a change from a non-activated to an activated conductivity only if T > 4 K, otherwise σ showed only a non-activated character. It is proposed that for T < 4 K the electron distribution function is mostly determined by optical and electric field excitations, which results in a non-activated conductivity. For T > 4 K thermal excitations become dominant which leads to an activated character of σ.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.