High-resolution calorimetry: limitations of doped semiconductor thermometers

Small thermal calorimeters operating at cryogenic temperatures have achieve d an energy resolution for single X-ray photons that is a factor of 20 bett er than the theoretical limit for a silicon ionization detector. To determi ne the potential for further improvements and decide on likely routes for a chieving them, we discuss detector design optimization, first for an ideal calorimeter, and then for the case where components exhibit non-ideal behav ior. Two serious non-ideal properties of doped semiconductor thermometers a re electron-phonon decoupling and excess noise. These have been characteriz ed over a range of sensitivity and operating temperature, and their effects on design optimization and ultimate performance can be evaluated. (C) 1999 Elsevier Science B.V. All rights reserved.