polymer molecules and others. Hopping conductivity of amorphous materials was one of the first examples of the application of this concept. For example, in the simplest 1D case the long time behavior of the carriers’ packet $n(x,t)$ for the particular realization of the random energy landscape $U(x)$ may be described by the diffusion equation $$\label{diffusion}
\frac{\partial n}{\partial t}=D_0 \frac{\partial}{\partial x}\left[\frac{\partial n}{\partial x}+\frac{1}{kT}\left(\frac{\partial U}
{\partial x}-eE\right)n\right].$$ Here $D_0$ is a bare diffusion coefficient in the absence of disorder and $E$ is the applied electric field. Dynamics of the carrier is a mixture of the diffusion and the drift induced by the action of the applied field. Characteristic features of the dynamics are governed by the density of states (DOS) $g(U)$ and statistical characteristics of the random energy landscape $U(x)$.

In many amorphous semiconductors the typical feature is an exponential tail of the DOS $$\label{exp-DOS}
g(U)\propto e^{U/U_0},\hskip10pt U < 0.$$ This feature to a very large extent determines charge transport properties of the materials. In inorganic semiconductors exponential DOS starts at some energy $U_c$ called transport edge and separating localized and extended states, though in some cases this energy could be located in the region of localized states [@Schiff:5265]. If states above 