  Semiconductor thermistors operating in the variable range hopping conduction
regime have been used in thermal detectors of all kinds for more than fifty
years. Their use in sensitive bolometers for infrared astronomy was a highly
developed empirical art even before the basic physics of the conduction
mechanism was understood. Today we are gradually obtaining a better
understanding of these devices, and with improvements in fabrication
technologies thermometers can now be designed and built with predictable
characteristics. There are still surprises, however, and it is clear that the
theory of their operation is not yet complete. In this chapter we give an
overview of the basic operation of doped semiconductor thermometers, outline
performance considerations, give references for empirical design and
performance data, and discuss fabrication issues.
