Electron glass: Intervalley transitions and the hopping conduction noise

The properties of the electron glass ground state and of those low-energy metastable states (valleys), in which the Coulomb potential at any occupied impurity is lower than that at any empty one, are studied by computer simulation. The transitions between just these states are expected to determine the low-frequency stochastic dynamics of the electron glass at low temperatures. The variation of the number of valleys, Nv, in samples with the same number of impurities, ND, but different arrangements, the shift of the Nv distribution to greater numbers with growing ND, the energy range of the valleys, the differences between the electron arrangements in different valleys in the same sample, and the activation energies for intervalley transitions are found. The energy range of the valleys is, at any ND, on the order of the characteristic Coulomb energy at the mean distance between impurities. Since the number of valleys grows with ND the mean distance between adjacent valley energies drops with ND. Despite the small differences between the valley energies the valleys are separated by energy barriers that, in samples with high number of ND and Nv, are distributed within a wide range. The width of this range grows with the size of the sample (ND) and with the number of valleys in it. This is an argument in favor of the idea that just the intervalley transitions are the source of low-frequency hopping conduction noise with the 1/f spectrum in lightly doped semiconductors at low temperatures. copyright 1998 The American Physical Society