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A variable-range hopping model is examined for transport in a band tail. For an exponential density of states the difference of the activation energies of conductivity and thermoelectric power, AE, is essentially determined by the steepness of the tail. AE varies slowly with tempera ture and depends little on the localization length a of the wave functions and on the magnitude of the density of states. From comparison of the results with experimental data it is suggested that this model applies to activated transport in n-type amorphous silicon.Mit Hilfe eines ,,variable-range-hopping"-Modells wird der Transport in Bandauslaufern untersucht. Der Unterschied AE der Aktivierungsenergien von Leitfihigkeit nnd Thermokraft wird hauptsachlich vom Abfallparameter LY der exponentiellen Zustandsdichte bestimmt. AE variiert schwach mit der Temperatur. Die Grolle der Zustandsdichte und die Lokalisierungslange haben einen kleinen EinfluB auf AE. Der Vergleich mit experimentellen Daten legt die Anwendbarkeit dieses Modells auf amorphes Silizium nahe.

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%'e present exact analytical and Monte Carlo results for zero-temperature diffusion and energy relaxation of excitations describable by Master-equation dynamics. %e demonstrate the freezing-in of relaxation at very low temperatures caused by "isolated" sites and clusters and observed experimentally in glassy benzophenone.Similar effects observed in semiconductor quantum-well structures and probably related to exciton trapping in disordered states caused by well-width fluctuations can be explained along the same lines. Asymptotic laws are derived and compared to Monte Carlo results. VVe also demonstrate that the departure from mean-field theories, serious for energy relaxation, is not so important for the diffusivity of excitations.