Variable-range hopping conductivity in Ge/GaAs thermometers at low temperatures: A summary of results

This is the authors' abstract. We don't add key points for this paper.

We have shown that the Ge/GaAs heterostructure is convenient for studying variable-range hopping conductivity in semiconductors. This is due to the ability to change the electrical conductivity in this heterostructure over a wide range. The electrical conductivity in this heterostructure is highly dependent on the manufacturing process. We developed cryogenic resistance thermometers based on this heterostructure. These thermometers can operate in the temperature ranges of 0.03 to 300 K, 1.5 to 300 K, and 4 to 400 K. We have manufactured, calibrated, and tested 90 thermometers across various models. At low temperatures, the conductivity of Ge film thermometers exhibits variable-range hopping with an exponent x = 0.25. This corresponds to the fact that the density of states at the Fermi level is nonzero. There are thermometers for which the exponent x for variable-range hopping conductivity is equal to 0.5, 0.45, and 0.6. This is observed in the presence of a Coulomb gap in the density of states, which is due to the Coulomb interaction. The difference in the values of x is apparently due to the different form of the density of states in the semiconductor impurity band. The parameters of various thermometers in the field of hopping conductivity are presented.