Novel observation of magnetic-field induced metal-insulator transition in n-GaAs through far-infrared photoconductivity measurements

We propose a novel technique to observe the magnetic-field induced metal-insulator transition (MFMIT) in GaAs through the far-infrared photoconductivity (FIRPC) measurements. Below the critical concentrations of the MIT, features of the FIRPC spectra with different donor concentrations are basically the same each other except that linewidths of the resonance spectra increase with increasing the donor concentration, Above the critical concentration of the MIT, drastic change in the magnetic field dependence of the FIRPC spectra has been observed for donors in GaAs. In this case, features of the FIRPC spectra show entirely new aspects: 1) The FIRPC spectra show a single resonance-like ones (SRS) and complicated structures of the FIRPC spectra observed in the insulator phase completely disappear. 2) We have observed anomalous shifts of the magnetic field, which gives the maximum of the absorption, with increasing the donor concentration and with rising the temperature. 3) The linewidths of the SRS for the FIRPC broaden as the donor concentration increases, We have discussed these phenomena taking into consideration the capture process by ionized donors for electrons excited by the FIR light.