4. ExperimentsThe experimental obse

4. ExperimentsThe experimental observation of conductance fluctuations in semiconductors has preceded the theoretical understanding of this phenomenon. Weak irregular conductance fluctuations in wide Si inversion layers were reported in 1965 by Howard and Fang.157 More pronounced fluctuations were found by Fowler et al. in narrow Si accumulation layers in the strongly localized regime.32 Kwasnick et al. made similar observations in narrow Si inversion layers in the metallic conduction regime.39 These fluctuations in the conductance as a function of gate voltage or magnetic field have been tentatively explained by various mechanisms.158 One of the explanations suggested is based on resonant tunneling,159 another on variable range hopping. At the 1984 conference on “Electronic Properties of Two-Dimensional Systems” Wheeler et al.161 and Skocpol et al.162 reported pronounced structure as a function of gate voltage in the low-temperature conductance of narrow Si inversion layers, observed in the course of their search for a quantum size effect.