Evidence for screening effects on the 1/f current noise in GaAs/AlGaAs modulation doped field effect transistors

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Abstract
Using a δ‐doped GaAs/AlGaAs heterostructure with a 10 nm spacer layer, we exploit the metastable nature of the DX centers at low temperatures to control electrostatically their net frozen charge density. The concentration of DX− centers at 77 K is only determined by the applied gate voltage Vc during the cool‐down of the sample to 77 K, i.e., it is independent, on the time scale of noise experiments, of the subsequent change in the gate bias VGS. The sheet carrier concentration ns of the two‐dimensional electron gas is varied through the application of VGS. Hall experiments performed at 77 K on gated Hall‐bar structures show that Vc strongly affects both, the threshold voltage Vt and the exponent k, which enters into the observed power‐law dependence of the Hall mobility μ on ns. These dependencies were also studied directly on modulation doped field effect transistors from the analysis of their transfer characteristics IDS–VGS and gme–VGS at low drain bias VDS. The 1/f drain‐current noise was investigated and, after subtraction of the noise arising from the series resistances, quantified by the extracted value of the channel‐associated Hooge parameter αch. This parameter is found to depend on ns and exhibits the same power‐law dependence as the reciprocal mobility 1/μ(ns). This striking correlation was established for various values of k and reveals screening effects on the 1/f noise. This correlation qualitatively supports the idea that the dominant mechanism of 1/f noise in modulation doped field effect transistors, at 77 K, is due to mobility fluctuations induced by screened fluctuations of Coulomb scattering, generated either by fluctuations of charge‐state and/or motion of defects.