Non-ideal effects in doped semiconductor thermistors

Semiconductor thermistors have been used for several years and their ideal behavior is well known both experimentally and theoretically. Their current performance is limited by non-ideal behaviors. These include 1/f noise and non-ohmic effects. We find that the 1/f noise appears to be a 2-D effect, and can be greatly reduced by fabricating thicker thermistors. Eliminating this noise could improve the intrinsic detector resolution as much as 40%. It also allows us to study other sources of excess noise in the thermometer. The non-ohmic behavior can be empirically explained using a hot-electron model. Although this model does not seem suitable for semiconductors in the variable range-hopping regime, where the electrons are localized, it fits the experimental data quite well. We measured an excess white noise at low frequencies consistent with the predicted thermodynamic fluctuations between electrons and phonons. We also measured a characteristic time of the non-ohmic behavior that is consistent with a C/G time constant in the hot electron model. Both results support the physical validity of the hot electron model. To optimize the performance of the next generation of detectors, we implemented the non-ideal behaviors in a model to predict the expected total noise and energy resolution. The comparison between the model and real data from the XRS experiment show good agreement.