Properties and applications of doped Ge thermistors

In the first half of this thesis, we discuss the importance of doped semiconductors for studies of disordered systems and review impurity conduction in the Ohmic limit. We then review the previous theoretical and experimental studies of non-Ohmic impurity conduction and discuss many contradictions between the existing studies. In particular, the dependence of the non-Ohmic conductivity on impurity concentration and temperature has not been established.;We describe three experimental studies of non-Ohmic impurity conduction in neutron transmutation doped germanium samples which have an extremely homogeneous, random impurity distribution. We find several new phenomena including a universal curve which describes the non-Ohmic behavior of lightly doped Ge:Ga samples, and a dramatic change in the non-Ohmic conductivity as the impurity concentration nears the critical concentration for a metal-insulator transition. We include a qualitative discussion of the effects of stress.;The second half of this thesis is concerned with various applications of doped Ge semiconductors. We present numerical methods for the global optimization of bolometric infrared detectors which use current-biased semiconducting thermistors. We explicitly include both the electric field dependence of the thermistor resistance and amplifier noise.;We present data from a novel low temperature particle detector which uses doped Ge thermistors as calorimeters. This detector uses a quasiparticle trapping mechanism to funnel athermal phonon energy from a large Ge absorber into a small doped Ge thermistor via a superconducting Al film.;We conclude with a description of an experiment which uses a doped Ge thermistor as part of a conventional low temperature bolometer for far infrared studies of the novel materials Sc;In the appendix we present measurements of the NJ132L JFET voltage noise as a function of temperature, drain voltage, and current. We discuss the fabrication of small, cooled JFET packages which can bolt to a helium cold plate and self-heat to a selected operating temperature, and we present an ultra-low noise voltage preamplifier design for room temperature operation.