Topic of the thesis is the investigation of semiconductor radiation detectors at cryogenic temperatures, which are based on the DEpleted P-channel Field Effect Transistor (DEPFET) active pixel sensor and the Blocked Impurity Band (BIB) detector concept. The DEPFET is a monolithic sensor-amplifier combination, which is able to determine the amount of signal electrons with very low noise. The BIB detector is a mid-infrared sensor, which is sensitive in the 5 µm to 40 µm bandwidth.
The main subject is the investigation of the basic detector's physical mechanisms at cryogenic conditions. It was the purpose of this thesis to develop a physical model for the properties of this active pixel sensor operated at cryogenic temperatures. Special emphasis was given to the amplification mechanisms of the DEPFET and the removal of trapped signal charge from the transistor's gate. A detailed modeling of the electric field inside the transistor's bulk was required to describe the device properties correctly. Based on the understanding of the electron dynamics in the signal collection area with electrons partially trapped in shallow donor states a method for complete signal charge reset was established. It is the basis for proper device operation and was successfully implemented. The predictions of the developed model and the experimental results were very good. The understanding of the device behaviour at cryogenic temperatures and the consistent experimental verification are a sound basis for the final integration of the DEPFET element in a mid-infrared detector system.