Diffused Germanium Resistors for Thermometry in 20 to 70°K Range

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Abstract
In studying the temperature variation of electrical conductivity of thin diffused layers in germanium, effects useful in thermometry have been found. For layers diffused with antimony in the range 3×1017 to 1×1018 cm−3, no impurity deionization is observed to temperatures as low as 13.9°K. Thus the variation of mobility in the layer determines the temperature dependence of resistivity. The mobility is observed to vary as μ=μ0Tn, with n close to unity in the range 20 to 70°K. This behavior makes such diffused resistors suitable for use as low temperature thermometers. By use of planar transistor technology n type resistors have been diffused into p type germanium. The resulting p‐n junction electrically isolates but thermally connects the resistor and the substrate. Thus the resistance element can be conductively coupled to the system to be measured. Since the diffused resistor is typically only 1 μ thick, thermometers having 1000 Ω resistance at 60°K are readily obtainable and two wire measurement is satisfactory. Indication of a step change in temperature from 60 to 20°K is essentially completed in 20 msec. Data on the stability of indication and magnetoresistance effect are presented, and use between 2 and 20°K is discussed.

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